【重拾View(一)】——setContentView()源码解析

1.【重拾View(一)】——setContentView()源码解析
2.【重拾View(二)】——LayoutInflater源码解析
3.【重拾View(三)】——LayoutInflater中Factory源码解析

前言

【重拾View】这个系列主要是想对View的各方面进行细化和回顾,随着Android研究的深入,对View的理解只停留在刚开始接触自定义View三部曲,简单知道onMeasure,onLayout,onDraw等仅仅和View相关联的使用层级的理解,感觉是远远不够的。本篇博客就分析一下我们最常见的一个方法setContentView,但是又没有真正关注过底层的实现。

层级关系

分析完本篇博客,会对下图有了更深对理解。


【重拾View(一)】——setContentView()源码解析_第1张图片
层级关系

主要流程源码

public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }


    public Window getWindow() {
        return mWindow;
    }

final void attach(){
    ...
    mWindow = new PhoneWindow(this, window, activityConfigCallback);
    ...
}

首先既然是setContentView,当然是在Activity下的方法,如上面的源码所示,可以看到,当我们调用setContentView的时候,实际上调用的是WinddowsetContentView方法,而Window是一个抽象类,真正的实现类,可以看到在Activityattach方法里,对Window进行里初始化,对应的实现类是PhoneWindow。所以接下来我们来看一下PhoneWindowsetContentView方法。

@Override
    public void setContentView(int layoutResID) {
        // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
        // decor, when theme attributes and the like are crystalized. Do not check the feature
        // before this happens.
        if (mContentParent == null) {
                //初始化DecorView
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }

        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
        } else {
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }

这里可以看到,在PhoneWindowsetContentView方法里,首先判读了mContentParent是否为空,这里暂时先不考虑mContentParent的作用,但是默认为空,所以这里可以看到,当mContentParent为空的时候,会走installDecor()方法,这个方法会初始化一个Android中耳熟能详的一个东西DecorView

private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            //生成了一个FrameLayout,作为DecorView
            mDecor = generateDecor(-1);
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
                //初始化mContentParent
            mContentParent = generateLayout(mDecor);

            // Set up decor part of UI to ignore fitsSystemWindows if appropriate.
            mDecor.makeOptionalFitsSystemWindows();

            final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById(
                    R.id.decor_content_parent);

            if (decorContentParent != null) {
                mDecorContentParent = decorContentParent;
                mDecorContentParent.setWindowCallback(getCallback());
                if (mDecorContentParent.getTitle() == null) {
                    mDecorContentParent.setWindowTitle(mTitle);
                }

                final int localFeatures = getLocalFeatures();
                for (int i = 0; i < FEATURE_MAX; i++) {
                    if ((localFeatures & (1 << i)) != 0) {
                        mDecorContentParent.initFeature(i);
                    }
                }

                mDecorContentParent.setUiOptions(mUiOptions);

                if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) != 0 ||
                        (mIconRes != 0 && !mDecorContentParent.hasIcon())) {
                    mDecorContentParent.setIcon(mIconRes);
                } else if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) == 0 &&
                        mIconRes == 0 && !mDecorContentParent.hasIcon()) {
                    mDecorContentParent.setIcon(
                            getContext().getPackageManager().getDefaultActivityIcon());
                    mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK;
                }
                if ((mResourcesSetFlags & FLAG_RESOURCE_SET_LOGO) != 0 ||
                        (mLogoRes != 0 && !mDecorContentParent.hasLogo())) {
                    mDecorContentParent.setLogo(mLogoRes);
                }

                // Invalidate if the panel menu hasn't been created before this.
                // Panel menu invalidation is deferred avoiding application onCreateOptionsMenu
                // being called in the middle of onCreate or similar.
                // A pending invalidation will typically be resolved before the posted message
                // would run normally in order to satisfy instance state restoration.
                PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
                if (!isDestroyed() && (st == null || st.menu == null) && !mIsStartingWindow) {
                    invalidatePanelMenu(FEATURE_ACTION_BAR);
                }
            } else {
                mTitleView = findViewById(R.id.title);
                if (mTitleView != null) {
                    if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {
                        final View titleContainer = findViewById(R.id.title_container);
                        if (titleContainer != null) {
                            titleContainer.setVisibility(View.GONE);
                        } else {
                            mTitleView.setVisibility(View.GONE);
                        }
                        mContentParent.setForeground(null);
                    } else {
                        mTitleView.setText(mTitle);
                    }
                }
            }

            if (mDecor.getBackground() == null && mBackgroundFallbackResource != 0) {
                mDecor.setBackgroundFallback(mBackgroundFallbackResource);
            }

            // Only inflate or create a new TransitionManager if the caller hasn't
            // already set a custom one.
            if (hasFeature(FEATURE_ACTIVITY_TRANSITIONS)) {
                if (mTransitionManager == null) {
                    final int transitionRes = getWindowStyle().getResourceId(
                            R.styleable.Window_windowContentTransitionManager,
                            0);
                    if (transitionRes != 0) {
                        final TransitionInflater inflater = TransitionInflater.from(getContext());
                        mTransitionManager = inflater.inflateTransitionManager(transitionRes,
                                mContentParent);
                    } else {
                        mTransitionManager = new TransitionManager();
                    }
                }

                mEnterTransition = getTransition(mEnterTransition, null,
                        R.styleable.Window_windowEnterTransition);
                mReturnTransition = getTransition(mReturnTransition, USE_DEFAULT_TRANSITION,
                        R.styleable.Window_windowReturnTransition);
                mExitTransition = getTransition(mExitTransition, null,
                        R.styleable.Window_windowExitTransition);
                mReenterTransition = getTransition(mReenterTransition, USE_DEFAULT_TRANSITION,
                        R.styleable.Window_windowReenterTransition);
                mSharedElementEnterTransition = getTransition(mSharedElementEnterTransition, null,
                        R.styleable.Window_windowSharedElementEnterTransition);
                mSharedElementReturnTransition = getTransition(mSharedElementReturnTransition,
                        USE_DEFAULT_TRANSITION,
                        R.styleable.Window_windowSharedElementReturnTransition);
                mSharedElementExitTransition = getTransition(mSharedElementExitTransition, null,
                        R.styleable.Window_windowSharedElementExitTransition);
                mSharedElementReenterTransition = getTransition(mSharedElementReenterTransition,
                        USE_DEFAULT_TRANSITION,
                        R.styleable.Window_windowSharedElementReenterTransition);
                if (mAllowEnterTransitionOverlap == null) {
                    mAllowEnterTransitionOverlap = getWindowStyle().getBoolean(
                            R.styleable.Window_windowAllowEnterTransitionOverlap, true);
                }
                if (mAllowReturnTransitionOverlap == null) {
                    mAllowReturnTransitionOverlap = getWindowStyle().getBoolean(
                            R.styleable.Window_windowAllowReturnTransitionOverlap, true);
                }
                if (mBackgroundFadeDurationMillis < 0) {
                    mBackgroundFadeDurationMillis = getWindowStyle().getInteger(
                            R.styleable.Window_windowTransitionBackgroundFadeDuration,
                            DEFAULT_BACKGROUND_FADE_DURATION_MS);
                }
                if (mSharedElementsUseOverlay == null) {
                    mSharedElementsUseOverlay = getWindowStyle().getBoolean(
                            R.styleable.Window_windowSharedElementsUseOverlay, true);
                }
            }
        }
    }

这个方法里我们需要注意两个方法:

generateDecor
generateLayout

if (mDecor == null) {
   mDecor = generateDecor(-1);
   ...
   } else {
   ...
   }

可以看到这里首先对mDecor进行了判空,而这个mDecor就是DecorView对象。

protected DecorView generateDecor(int featureId) {
        // System process doesn't have application context and in that case we need to directly use
        // the context we have. Otherwise we want the application context, so we don't cling to the
        // activity.
        Context context;
        if (mUseDecorContext) {
            Context applicationContext = getContext().getApplicationContext();
            if (applicationContext == null) {
                context = getContext();
            } else {
                context = new DecorContext(applicationContext, getContext().getResources());
                if (mTheme != -1) {
                    context.setTheme(mTheme);
                }
            }
        } else {
            context = getContext();
        }
        return new DecorView(context, featureId, this, getAttributes());
    }

可以看到,这里最终就是new了一个DecorView对象。而我们来看一下DecorView对源码。

public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {

可以发现其实DecorView实际上就是一个FrameLayout。

if (mContentParent == null) {
                //初始化mContentParent
            mContentParent = generateLayout(mDecor);
}

可以看到这里初始化完DecorView后便开始创建mContentParent

protected ViewGroup generateLayout(DecorView decor) {
        // Apply data from current theme.

        TypedArray a = getWindowStyle();

        if (false) {
            System.out.println("From style:");
            String s = "Attrs:";
            for (int i = 0; i < R.styleable.Window.length; i++) {
                s = s + " " + Integer.toHexString(R.styleable.Window[i]) + "="
                        + a.getString(i);
            }
            System.out.println(s);
        }
        //Activity是否是浮动的,一般用于Dialog窗口的浮动
        mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);
        int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
                & (~getForcedWindowFlags());
        if (mIsFloating) {
            setLayout(WRAP_CONTENT, WRAP_CONTENT);
            setFlags(0, flagsToUpdate);
        } else {
            setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
        }
        //activity是否没有标题
        if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
            requestFeature(FEATURE_NO_TITLE);
        } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
            // Don't allow an action bar if there is no title.
            requestFeature(FEATURE_ACTION_BAR);
        }

        if (a.getBoolean(R.styleable.Window_windowActionBarOverlay, false)) {
            requestFeature(FEATURE_ACTION_BAR_OVERLAY);
        }

        if (a.getBoolean(R.styleable.Window_windowActionModeOverlay, false)) {
            requestFeature(FEATURE_ACTION_MODE_OVERLAY);
        }

        if (a.getBoolean(R.styleable.Window_windowSwipeToDismiss, false)) {
            requestFeature(FEATURE_SWIPE_TO_DISMISS);
        }
        //activity是否全屏
        if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {
            setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowTranslucentStatus,
                false)) {
            setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS
                    & (~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowTranslucentNavigation,
                false)) {
            setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION
                    & (~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowOverscan, false)) {
            setFlags(FLAG_LAYOUT_IN_OVERSCAN, FLAG_LAYOUT_IN_OVERSCAN&(~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowShowWallpaper, false)) {
            setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));
        }

        if (a.getBoolean(R.styleable.Window_windowEnableSplitTouch,
                getContext().getApplicationInfo().targetSdkVersion
                        >= android.os.Build.VERSION_CODES.HONEYCOMB)) {
            setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags()));
        }

        a.getValue(R.styleable.Window_windowMinWidthMajor, mMinWidthMajor);
        a.getValue(R.styleable.Window_windowMinWidthMinor, mMinWidthMinor);
        if (DEBUG) Log.d(TAG, "Min width minor: " + mMinWidthMinor.coerceToString()
                + ", major: " + mMinWidthMajor.coerceToString());
        if (a.hasValue(R.styleable.Window_windowFixedWidthMajor)) {
            if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedWidthMajor,
                    mFixedWidthMajor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedWidthMinor)) {
            if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedWidthMinor,
                    mFixedWidthMinor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedHeightMajor)) {
            if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedHeightMajor,
                    mFixedHeightMajor);
        }
        if (a.hasValue(R.styleable.Window_windowFixedHeightMinor)) {
            if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue();
            a.getValue(R.styleable.Window_windowFixedHeightMinor,
                    mFixedHeightMinor);
        }
        if (a.getBoolean(R.styleable.Window_windowContentTransitions, false)) {
            requestFeature(FEATURE_CONTENT_TRANSITIONS);
        }
        if (a.getBoolean(R.styleable.Window_windowActivityTransitions, false)) {
            requestFeature(FEATURE_ACTIVITY_TRANSITIONS);
        }

        mIsTranslucent = a.getBoolean(R.styleable.Window_windowIsTranslucent, false);

        final Context context = getContext();
        final int targetSdk = context.getApplicationInfo().targetSdkVersion;
        final boolean targetPreHoneycomb = targetSdk < android.os.Build.VERSION_CODES.HONEYCOMB;
        final boolean targetPreIcs = targetSdk < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH;
        final boolean targetPreL = targetSdk < android.os.Build.VERSION_CODES.LOLLIPOP;
        final boolean targetHcNeedsOptions = context.getResources().getBoolean(
                R.bool.target_honeycomb_needs_options_menu);
        final boolean noActionBar = !hasFeature(FEATURE_ACTION_BAR) || hasFeature(FEATURE_NO_TITLE);

        if (targetPreHoneycomb || (targetPreIcs && targetHcNeedsOptions && noActionBar)) {
            setNeedsMenuKey(WindowManager.LayoutParams.NEEDS_MENU_SET_TRUE);
        } else {
            setNeedsMenuKey(WindowManager.LayoutParams.NEEDS_MENU_SET_FALSE);
        }

        if (!mForcedStatusBarColor) {
            mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
        }
        if (!mForcedNavigationBarColor) {
            mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000);
        }

        WindowManager.LayoutParams params = getAttributes();

        // Non-floating windows on high end devices must put up decor beneath the system bars and
        // therefore must know about visibility changes of those.
        if (!mIsFloating && ActivityManager.isHighEndGfx()) {
            if (!targetPreL && a.getBoolean(
                    R.styleable.Window_windowDrawsSystemBarBackgrounds,
                    false)) {
                setFlags(FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS,
                        FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS & ~getForcedWindowFlags());
            }
            if (mDecor.mForceWindowDrawsStatusBarBackground) {
                params.privateFlags |= PRIVATE_FLAG_FORCE_DRAW_STATUS_BAR_BACKGROUND;
            }
        }
        if (a.getBoolean(R.styleable.Window_windowLightStatusBar, false)) {
            decor.setSystemUiVisibility(
                    decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR);
        }

        if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion
                >= android.os.Build.VERSION_CODES.HONEYCOMB) {
            if (a.getBoolean(
                    R.styleable.Window_windowCloseOnTouchOutside,
                    false)) {
                setCloseOnTouchOutsideIfNotSet(true);
            }
        }
        //设置输入法的状态
        if (!hasSoftInputMode()) {
            params.softInputMode = a.getInt(
                    R.styleable.Window_windowSoftInputMode,
                    params.softInputMode);
        }

        if (a.getBoolean(R.styleable.Window_backgroundDimEnabled,
                mIsFloating)) {
            /* All dialogs should have the window dimmed */
            if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) {
                params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND;
            }
            if (!haveDimAmount()) {
                params.dimAmount = a.getFloat(
                        android.R.styleable.Window_backgroundDimAmount, 0.5f);
            }
        }
        //Activity的进入动画
        if (params.windowAnimations == 0) {
            params.windowAnimations = a.getResourceId(
                    R.styleable.Window_windowAnimationStyle, 0);
        }

        // The rest are only done if this window is not embedded; otherwise,
        // the values are inherited from our container.
        if (getContainer() == null) {
            if (mBackgroundDrawable == null) {
                if (mBackgroundResource == 0) {
                    mBackgroundResource = a.getResourceId(
                            R.styleable.Window_windowBackground, 0);
                }
                if (mFrameResource == 0) {
                    mFrameResource = a.getResourceId(R.styleable.Window_windowFrame, 0);
                }
                mBackgroundFallbackResource = a.getResourceId(
                        R.styleable.Window_windowBackgroundFallback, 0);
                if (false) {
                    System.out.println("Background: "
                            + Integer.toHexString(mBackgroundResource) + " Frame: "
                            + Integer.toHexString(mFrameResource));
                }
            }
            if (mLoadElevation) {
                mElevation = a.getDimension(R.styleable.Window_windowElevation, 0);
            }
            mClipToOutline = a.getBoolean(R.styleable.Window_windowClipToOutline, false);
            mTextColor = a.getColor(R.styleable.Window_textColor, Color.TRANSPARENT);
        }

        // Inflate the window decor.

        int layoutResource;
        int features = getLocalFeatures();
        // System.out.println("Features: 0x" + Integer.toHexString(features));
        //根据不同的features选择不同布局进行加载
        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            layoutResource = R.layout.screen_swipe_dismiss;
            setCloseOnSwipeEnabled(true);
        } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogTitleIconsDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else {
                layoutResource = R.layout.screen_title_icons;
            }
            // XXX Remove this once action bar supports these features.
            removeFeature(FEATURE_ACTION_BAR);
            // System.out.println("Title Icons!");
        } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
                && (features & (1 << FEATURE_ACTION_BAR)) == 0) {
            // Special case for a window with only a progress bar (and title).
            // XXX Need to have a no-title version of embedded windows.
            layoutResource = R.layout.screen_progress;
            // System.out.println("Progress!");
        } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
            // Special case for a window with a custom title.
            // If the window is floating, we need a dialog layout
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogCustomTitleDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else {
                layoutResource = R.layout.screen_custom_title;
            }
            // XXX Remove this once action bar supports these features.
            removeFeature(FEATURE_ACTION_BAR);
        } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
            // If no other features and not embedded, only need a title.
            // If the window is floating, we need a dialog layout
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogTitleDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
                layoutResource = a.getResourceId(
                        R.styleable.Window_windowActionBarFullscreenDecorLayout,
                        R.layout.screen_action_bar);
            } else {
                layoutResource = R.layout.screen_title;
            }
            // System.out.println("Title!");
        } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
            layoutResource = R.layout.screen_simple_overlay_action_mode;
        } else {
            // Embedded, so no decoration is needed.
            layoutResource = R.layout.screen_simple;
            // System.out.println("Simple!");
        }

        mDecor.startChanging();
        //加载布局,并加入DecorView
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
        //通过findViewById,找到内容区域,是一个FrameLayout
        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }

        if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
            ProgressBar progress = getCircularProgressBar(false);
            if (progress != null) {
                progress.setIndeterminate(true);
            }
        }

        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            registerSwipeCallbacks(contentParent);
        }

        // Remaining setup -- of background and title -- that only applies
        // to top-level windows.
        if (getContainer() == null) {
            final Drawable background;
            if (mBackgroundResource != 0) {
                background = getContext().getDrawable(mBackgroundResource);
            } else {
                background = mBackgroundDrawable;
            }
            mDecor.setWindowBackground(background);

            final Drawable frame;
            if (mFrameResource != 0) {
                frame = getContext().getDrawable(mFrameResource);
            } else {
                frame = null;
            }
            mDecor.setWindowFrame(frame);

            mDecor.setElevation(mElevation);
            mDecor.setClipToOutline(mClipToOutline);

            if (mTitle != null) {
                setTitle(mTitle);
            }

            if (mTitleColor == 0) {
                mTitleColor = mTextColor;
            }
            setTitleColor(mTitleColor);
        }

        mDecor.finishChanging();

        return contentParent;
    }

这个方法比较长,我们会发现和我们自定义View的步骤很相近,这里首先获取了自定义属性,然后分别设置了一些属性值。

//Activity是否是浮动的,一般用于Dialog窗口的浮动
        mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);
        int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
                & (~getForcedWindowFlags());
        if (mIsFloating) {
            setLayout(WRAP_CONTENT, WRAP_CONTENT);
            setFlags(0, flagsToUpdate);
        } else {
            setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
        }
        
        //activity是否没有标题
        if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
            requestFeature(FEATURE_NO_TITLE);
        } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
            // Don't allow an action bar if there is no title.
            requestFeature(FEATURE_ACTION_BAR);
        }
        
        //activity是否全屏
        if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {
            setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
        }
        
        //设置输入法的状态
        if (!hasSoftInputMode()) {
            params.softInputMode = a.getInt(
                    R.styleable.Window_windowSoftInputMode,
                    params.softInputMode);
        }
        
        //Activity的进入动画
        if (params.windowAnimations == 0) {
            params.windowAnimations = a.getResourceId(
                    R.styleable.Window_windowAnimationStyle, 0);
        }

可以看到我们在xml里面设置的属性值在这里就生效了,具体还有其他的属性值这里就不具体分析了。

//根据不同的features选择不同布局进行加载
        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            layoutResource = R.layout.screen_swipe_dismiss;
            setCloseOnSwipeEnabled(true);
        } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogTitleIconsDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else {
                layoutResource = R.layout.screen_title_icons;
            }
            // XXX Remove this once action bar supports these features.
            removeFeature(FEATURE_ACTION_BAR);
            // System.out.println("Title Icons!");
        } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
                && (features & (1 << FEATURE_ACTION_BAR)) == 0) {
            // Special case for a window with only a progress bar (and title).
            // XXX Need to have a no-title version of embedded windows.
            layoutResource = R.layout.screen_progress;
            // System.out.println("Progress!");
        } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
            // Special case for a window with a custom title.
            // If the window is floating, we need a dialog layout
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogCustomTitleDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else {
                layoutResource = R.layout.screen_custom_title;
            }
            // XXX Remove this once action bar supports these features.
            removeFeature(FEATURE_ACTION_BAR);
        } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
            // If no other features and not embedded, only need a title.
            // If the window is floating, we need a dialog layout
            if (mIsFloating) {
                TypedValue res = new TypedValue();
                getContext().getTheme().resolveAttribute(
                        R.attr.dialogTitleDecorLayout, res, true);
                layoutResource = res.resourceId;
            } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
                layoutResource = a.getResourceId(
                        R.styleable.Window_windowActionBarFullscreenDecorLayout,
                        R.layout.screen_action_bar);
            } else {
                layoutResource = R.layout.screen_title;
            }
            // System.out.println("Title!");
        } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
            layoutResource = R.layout.screen_simple_overlay_action_mode;
        } else {
            // Embedded, so no decoration is needed.
            layoutResource = R.layout.screen_simple;
            // System.out.println("Simple!");
        }

接下来这段代码的作用就是确定最终的布局文件,可以看到这里用到了很多的ifelse,这里通过位运算符和feature进行比较,可能这里说feature比较陌生,我们平常设置我们的Activity全屏的时候,常用的一段代码就是:

requestWindowFeature(Window.FEATURE_NO_TITLE);

这里就是改变feature的属性,所以这里当我们没有特殊设置的的时候,最终最选择使用R.layout.screen_simple;这个布局文件。


    
    

可以看到,这就是一个再平常不过的布局文件了,一个LinearLayout,第一个ViewStub不会默认加载,还剩一个FrameLayout,注意这里的id@android:id/content。我们继续后面的代码

mDecor.startChanging();
        //加载布局,并加入DecorView
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
        //通过findViewById,找到内容区域,是一个FrameLayout
        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }

可以看到这里其实有两部操作

1.将刚才的布局加入到DecorView中
2.返回DecorView中的FrameLayout,也就是刚才布局。

void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
        mStackId = getStackId();

        if (mBackdropFrameRenderer != null) {
            loadBackgroundDrawablesIfNeeded();
            mBackdropFrameRenderer.onResourcesLoaded(
                    this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
                    mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
                    getCurrentColor(mNavigationColorViewState));
        }

        mDecorCaptionView = createDecorCaptionView(inflater);
        //用LayoutInflater加载布局文件
        final View root = inflater.inflate(layoutResource, null);
        if (mDecorCaptionView != null) {
            if (mDecorCaptionView.getParent() == null) {
                addView(mDecorCaptionView,
                        new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
            }
            mDecorCaptionView.addView(root,
                    new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));
        } else {
        //加入到DecorView中
            // Put it below the color views.
            addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
        }
        mContentRoot = (ViewGroup) root;
        initializeElevation();
    }

这里可以看一下onResourcesLoaded方法,我们将刚才R.layout.screen_simple;的布局文件传入,可以看到这里先用LayoutInflater加载这个布局文件,注意这里并没有直接通过LayoutInflater将布局文件加入DecorView中,而是先通过一个判断,这里应该是一个可以优先级较高的布局,但是不影响流程分析,这里就不纠结了,可以看到,在后面,通过addView方法,将这个布局文件,加入到DecorView中。

//通过findViewById,找到内容区域,是一个FrameLayout
        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }
//前面布局文件中看到的FrameLayout的Id        
public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;

加入到DecorView中,通过findViewById方法,注意这里寻找到Id就是我们前面在布局R.layout.screen_simple;看到的那个FrameLayout的ID。

 protected ViewGroup generateLayout(DecorView decor) {
            ....
        return contentParent;
    }

所以这里可以发现,generateLayout方法回将布局文件中的FrameLayout加载并返回。而这时候我们在往回看。

private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            mDecor = generateDecor(-1);
            ...
           } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
        //获取到布局文件中的FrameLayout
            mContentParent = generateLayout(mDecor);
}

这里回将这个FrameLayout赋值给mContentParent,这时候我们再回过头来看我们最开始PhoneWindow中的setContentView方法。

@Override
    public void setContentView(int layoutResID) {
        if (mContentParent == null) {
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }

        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
        } else {
        //通过LayoutInflater将我们Activity的布局文件,加载到FrameLayout中
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }

当我们加载完系统的FrameLayout,并赋值到mContentParent中,后面还是通过LayoutInflater将我们Activity传入的布局文件加载到FrameLayout中。这时,我们自己定义的布局文件就完成了加入到手机的页面中。

细节分析

1.requestWindowFeature(Window.FEATURE_NO_TITLE)需要在setContentView之前调用

我们平常设置我们的Activity全屏的时候,常用的一段代码就是:

requestWindowFeature(Window.FEATURE_NO_TITLE);

而且这段代码需要在setContentView之前调用,这里就可以连起来,我们在setContentView之前调用requestWindowFeature(Window.FEATURE_NO_TITLE);改变了feature属性,然后在setContentView的时候,再读取feature属性,发现需要全屏,则使用的是全屏的布局文件,不包含标题栏。

//Activity中最后设置了mLocalFeatures
public boolean requestFeature(int featureId) {
        final int flag = 1<

从上面的代码也验证了我们的猜想。

2.setContentView在不同Activity的差异

我们来看一下android.app.Activity和android.support.v7.app.AppCompatActivity的差异

android.app.Activity.class
public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }
  android.support.v7.app.AppCompatActivity.class  
    @Override
    public void setContentView(@LayoutRes int layoutResID) {
        getDelegate().setContentView(layoutResID);
    }

可以看到,v7包下并不是直接使用PhoneWindowsetContentView方法。而是使用了一个代理。

@NonNull
    public AppCompatDelegate getDelegate() {
        if (mDelegate == null) {
            mDelegate = AppCompatDelegate.create(this, this);
        }
        return mDelegate;
    }
    
    private static AppCompatDelegate create(Context context, Window window,
            AppCompatCallback callback) {
        if (Build.VERSION.SDK_INT >= 24) {
            return new AppCompatDelegateImplN(context, window, callback);
        } else if (Build.VERSION.SDK_INT >= 23) {
            return new AppCompatDelegateImplV23(context, window, callback);
        } else if (Build.VERSION.SDK_INT >= 14) {
            return new AppCompatDelegateImplV14(context, window, callback);
        } else if (Build.VERSION.SDK_INT >= 11) {
            return new AppCompatDelegateImplV11(context, window, callback);
        } else {
            return new AppCompatDelegateImplV9(context, window, callback);
        }
    }

果然,Goolge爸爸为了适配费尽心机~,最后我们会发现,上面的都是子类父类的关系,AppCompatDelegateImplN-> AppCompatDelegateImplV23-> AppCompatDelegateImplV14-> AppCompatDelegateImplV11-> AppCompatDelegateImplV9,所以这里调用的setContentView都是使用的AppCompatDelegateImplV9中的方法。

@Override
    public void setContentView(int resId) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        LayoutInflater.from(mContext).inflate(resId, contentParent);
        mOriginalWindowCallback.onContentChanged();
    }

可以看到,原理上大同小异,只不过,这里不是由Window发起的,而是换了一种方式。

总结

本篇博客主要分析的是setContentView的源码,这里回顾一下前面分析得到的过程。

1.实质调用的是window的setContentView方法,window是在Activity的attach方法里创建的,实现类是PhoneWindow
2.首先创建DecorView,实质就是一个FrameLayout
3.根据Feature(例如是否有标题栏)选择一个系统布局文件,然后加入到DecorView中。
4.默认是一个常规的LinearLayout嵌套FrameLayout,而FrameLayout就是我们所熟知的id为content的副布局。
5.最后通过LayoutInflater将我们自己创建的Activity布局文件加入到刚才那个名为content的FrameLayout中。

通过这次分析我们对下图,也就是我们常见的一个Android页面层级关系有了一个很深的认识,当然我们也会发现LayoutInflater这个我们常用类的重要性,下一篇博客会对该类进行分析。

【重拾View(一)】——setContentView()源码解析_第2张图片
层级关系

推荐&学习&参考博客

从setContentView方法分析Android加载布局流程
自定义View(七)-View的工作原理- Activity的布局加载
Android setContentView 源码解析

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