Android进阶——Android弹窗组件工作机制之Dialog、DialogFragment

前言

Android在DialogFragment推出后，就已经不推荐继续使用Dialog，可替换为DialogFragment，其实DialogFragment只不过是对增加一层看不到的Fragment，用于监听生命周期，在Activity退出的时候会自动回收Dialog弹窗

基础概念

• Activity：活动。控制生命周期和处理事件，统筹视图的添加与显示，控制Window和View的交互
• Window：窗口。在Android中是个虚拟的概念，不是View，是承载View的载体，具体实现是PhoneWindow，承载着DecorView
• WindowManager：窗口管理者。管理Window视图的添加或移除等，具体实现是WindowManagerService（wms）
• DecorView：窗口根视图。本身是FrameLayout，是Window上真正的根布局，其包含两部分，标题和内容
• TitleView：标题。作为DecorView的子View，其Id为@android:id/content
• ContentViews：内容。作为DecorView的子View，其Id为@android:id/content
• ViewRoot：连接wms和DecorView的纽带，View的measure、layout、draw均通过ViewRoot来完成，具体实现是ViewRootImpl

Dialog

在平时中，简单的弹出Dialog只需要这句话

new Dialog(MainActivity.this).show();

一、Dialog的显示

1、Dialog

Dialog的构造方法有多个，但最后都会调用这个构造方法

Dialog(@NonNull Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
    if (createContextThemeWrapper) {
        if (themeResId == 0) {
            //如果没有主题，则使用默认主题
            final TypedValue outValue = new TypedValue();
            context.getTheme().resolveAttribute(R.attr.dialogTheme, outValue, true);
            themeResId = outValue.resourceId;
        }
        //包裹主题的Context
        mContext = new ContextThemeWrapper(context, themeResId);
    } else {
        mContext = context;
    }
    //获取windowManager服务
    mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    //创建新的Window
    final Window w = new PhoneWindow(mContext);
    mWindow = w;
    //设置callback
    w.setCallback(this);
    w.setOnWindowDismissedCallback(this);
    w.setWindowManager(mWindowManager, null, null);
    w.setGravity(Gravity.CENTER);
 
    mListenersHandler = new ListenersHandler(this);
}

从Dialog的构造方法中可以看出，Dialog实质上是个Window，其显示和隐藏也是借助WindowManager去控制的

2、Dialog.show

public void show() {
    //如果之前已经show过后，就让视图显示即可
    if (mShowing) {        
        if (mDecor != null) {            
            if (mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {                
                mWindow.invalidatePanelMenu(Window.FEATURE_ACTION_BAR);            
            }            
            mDecor.setVisibility(View.VISIBLE);        
        }        
        return;   
    }    
    mCanceled = false;    
    
    //如果没有create则会调用dispatchOncreate，该方法最终会调用dialog的onCreate方法
    if (!mCreated) {
        dispatchOnCreate(null);
    }
 
    //dialog的onstart回调
    onStart();
    //获取decorView
    mDecor = mWindow.getDecorView();
 
    //如果需要ActionBar，则创建出来
    if (mActionBar == null && mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {
        final ApplicationInfo info = mContext.getApplicationInfo();
        mWindow.setDefaultIcon(info.icon);
        mWindow.setDefaultLogo(info.logo);
        mActionBar = new WindowDecorActionBar(this);
    }
 
    //window参数的设置
    WindowManager.LayoutParams l = mWindow.getAttributes();
    if ((l.softInputMode
            & WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION) == 0) {
        WindowManager.LayoutParams nl = new WindowManager.LayoutParams();
        nl.copyFrom(l);
        nl.softInputMode |=
                WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
        l = nl;
    }
 
    try {
        //windowManager将decorView加入视图
        mWindowManager.addView(mDecor, l);
        mShowing = true;
 
        sendShowMessage();
    } finally {
    }
}

show()其实就是走Dialog的生命周期，然后做初始化工作，获取Window上的DecorView后，将DecorView添加到视图上，这里需要注意的是在show()之后才执行onCreate()

3、Dialog.dispatchOnCreate

void dispatchOnCreate(Bundle savedInstanceState) {
    if (!mCreated) {
        onCreate(savedInstanceState); //回调onCreate()
        mCreated = true;
    }
}

protected void onCreate(Bundle savedInstanceState) {
    //由开发者实现
}

Dialog的初始化其实就是让用户去初始化自己的视图，平时我们是这么写的

public class RxDialog extends Dialog {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //设置视图
        setContentView(mView);
    }
}

具体的逻辑还是回到setContentView()设置Dialog的视图

4、Dialog.setContentView

public void setContentView(View view) {
    //调用mWindow进行视图设置，mWindow实际上就是构造方法中的PhoneWindow
    mWindow.setContentView(view);
}

mWindow则是在构造方法创建的PhoneWindow

5、PhoneWindow.setContentView

@Override
public void setContentView(View view) {
    //默认MATCH_PARENT
    setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}

@Override
public void setContentView(View view, ViewGroup.LayoutParams params) {
    if (mContentParent == null) {  
        installDecor();  //创建应用程序窗口视图对象
    } else {  
        mContentParent.removeAllViews();  //重新设置应用程序窗口的视图
    }  
 
    if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
        view.setLayoutParams(params);
        final Scene newScene = new Scene(mContentParent, view);
        transitionTo(newScene);
    } else {
        mContentParent.addView(view, params); //将我们传递进来的view添加布局上
    }
    mContentParent.requestApplyInsets();
    final Callback cb = getCallback();
    if (cb != null && !isDestroyed()) {
        cb.onContentChanged();
    }
    
    ......
}

PhoneWindow.setContentView()不仅在Dialog中存在，在Activity的setContentView也是走到这里。mContentParent指的是依附于DecorView上的R.id.content中的view。到这里只是将Dialog设置的View加载到PhoneWindow的ContentView上，其实更主要的还是PhoneWindow添加到我们的手机屏幕上，代码回溯到show()的mWindowManager.addView(mDecor, l)

6、WindowManagerImpl.addView

WindowManager本质上是对View进行管理，但是WindowManager显然依然是个接口，其具体实现是WindowManagerImpl，最后还是委托给WindowManagerGlobal实例mGlobal处理

@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyDefaultToken(params);
    //委托给mGlobal来进行实现
    mGlobal.addView(view, params, mDisplay, mParentWindow);
}

7、WindowManagerGlobal.addView

public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {
    
    ......
    
    final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
    if (parentWindow != null) {
        parentWindow.adjustLayoutParamsForSubWindow(wparams);
    } else {
        // If there's no parent, then hardware acceleration for this view is
        // set from the application's hardware acceleration setting.
        final Context context = view.getContext();
        if (context != null
                && (context.getApplicationInfo().flags
                        & ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
            wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
        }
    }
 
    ViewRootImpl root;
    View panelParentView = null;
 
    synchronized (mLock) {
        // Start watching for system property changes.
        if (mSystemPropertyUpdater == null) {
            mSystemPropertyUpdater = new Runnable() {
                @Override public void run() {
                    synchronized (mLock) {
                        for (int i = mRoots.size() - 1; i >= 0; --i) {
                            mRoots.get(i).loadSystemProperties();
                        }
                    }
                }
            };
            SystemProperties.addChangeCallback(mSystemPropertyUpdater);
        }
 
        int index = findViewLocked(view, false);
        if (index >= 0) {
            if (mDyingViews.contains(view)) {
                // Don't wait for MSG_DIE to make it's way through root's queue.
                mRoots.get(index).doDie();
            } else {
                throw new IllegalStateException("View " + view
                        + " has already been added to the window manager.");
            }
            // The previous removeView() had not completed executing. Now it has.
        }
 
        // If this is a panel window, then find the window it is being
        // attached to for future reference.
        if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
                wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
            final int count = mViews.size();
            for (int i = 0; i < count; i++) {
                if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
                    panelParentView = mViews.get(i);
                }
            }
        }
 
        //创建ViewRootImpl，ViewRootImpl是view和window中的连接纽带
        root = new ViewRootImpl(view.getContext(), display);
 
        view.setLayoutParams(wparams);
        
        //存储相关View的信息，会在Remove的时候移除，相当于缓存
        mViews.add(view);//mViews：存储的是所有Window对应的View，本质是个List
        mRoots.add(root);//mRoots：存储的是所有Window所对应的ViewRootImpl，本质是个List
        mParams.add(wparams);//mParams：存储所有window对应的布局参数，本质是个List
    }
 
    // do this last because it fires off messages to start doing things
    try {
        //最终由root去实现最终的视图显示
        root.setView(view, wparams, panelParentView);
    } catch (RuntimeException e) {
        // BadTokenException or InvalidDisplayException, clean up.
        synchronized (mLock) {
            final int index = findViewLocked(view, false);
            if (index >= 0) {
                removeViewLocked(index, true);
            }
        }
        throw e;
    }
}

将视图添加到窗口上的工作交给root.setView()，root就是ViewRootImpl

8、ViewRootImpl.setView

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
    synchronized (this) {
        if (mView == null) {
            ......
            requestLayout(); //真正完成视图的异步刷新请求
            
            ......
            //这里调用了mWindowSession的addToDisplay方法，在WindowManagerService层通过IPC机制完成真正的window添加
            res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                    getHostVisibility(), mDisplay.getDisplayId(),
                    mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                    mAttachInfo.mOutsets, mInputChannel);
           
        }
    }
}

@Override
public void requestLayout() {
    if (!mHandlingLayoutInLayoutRequest) {
        checkThread();
        mLayoutRequested = true;
        scheduleTraversals(); //真正的去走Measure、Layout、Draw
    }
}

在添加view之前，会走requestLayout()，真正实现View绘制的三部曲Measure、Layout、Draw。mWindowSession类型是IWindowSession，它是个Binder对象，真正的实现类是Session，window的添加过程实际上是一次ipc的调用，最后在WindowManagerService层通过IPC机制去实现的

总结

在这读完这里源码后，我们知道Window是个相对虚拟的对象，真正的操作是对Window中的DecorView进行addView()操作，而且在addView()之前，会先走onCreate()、onStart()、setContentView()操作，而在setContentView()过程中，会经过ViewRootImpl对象进行setView，并且在ViewRootImpl对象中会实现View绘制的三步曲，Measure、Layout、Draw操作，最后再将绘制好的view通过IWindowSession的ipc调用添加到界面上

1. Dialog本质上是个Window，具体是通过Window的DecorView进行显示的
2. Dialog是在show()之后走的onCreate()、onStart()、setContentView()等回调

二、Dialog的消失

1、dismiss

private final Runnable mDismissAction = this::dismissDialog;

public void dismiss() {
    if (Looper.myLooper() == mHandler.getLooper()) {
        dismissDialog();
    } else {
        mHandler.post(mDismissAction);
    }
}

保证UI操作都在主线程执行，而且引用了Java8新特性写法this::dismissDialog，最后都会调用dismissDialog()

2、dismissDialog

void dismissDialog() {
    if (mDecor == null || !mShowing) {
        return;
    }
 
    if (mWindow.isDestroyed()) {
        Log.e(TAG, "Tried to dismissDialog() but the Dialog's window was already destroyed!");
        return;
    }
 
    try {
        //这里移除DecorView
        mWindowManager.removeViewImmediate(mDecor);
    } finally {
        if (mActionMode != null) {
            mActionMode.finish();
        }
        mDecor = null;
        mWindow.closeAllPanels();
        onStop();
        mShowing = false;
 
        sendDismissMessage();
    }
}

从show中知道，我们将DecorView加入到WindowManager中去，所以这里移除的是DecorView

3、WindowManagerImpl.removeViewImmediate

public void removeViewImmediate(View view) {
    //委托给mGlobal来进行实现
    mGlobal.removeView(view, true);
}

同样的交给WindowManagerGlobal去处理

4、WindowManagerGlobal.removeView

public void removeView(View view, boolean immediate) {
    if (view == null) {
        throw new IllegalArgumentException("view must not be null");
    }
 
    synchronized (mLock) {
        //待remove view的索引
        int index = findViewLocked(view, true);
        //mRoots保存着每一个viewRootImpl对象
        View curView = mRoots.get(index).getView();
        //真正对view进行了remove操作
        removeViewLocked(index, immediate);
        if (curView == view) {
            return;
        }
 
        throw new IllegalStateException("Calling with view " + view
                + " but the ViewAncestor is attached to " + curView);
    }
}

找到对应要移除的View后进行View逻辑处理工作

5、WindowManagerGlobal.removeViewLocked

private void removeViewLocked(int index, boolean immediate) {
    ViewRootImpl root = mRoots.get(index);
    View view = root.getView();
 
    if (view != null) {
        InputMethodManager imm = InputMethodManager.getInstance();
        if (imm != null) {
            imm.windowDismissed(mViews.get(index).getWindowToken());
        }
    }
    //重点在ViewRootImpl中的die方法中
    boolean deferred = root.die(immediate);
    if (view != null) {
        view.assignParent(null);
        if (deferred) {
            mDyingViews.add(view);
        }
    }
}

找到对应的ViewRootImpl，进行移除并释放工作

6、ViewRootImpl.die

boolean die(boolean immediate) {
    if (immediate && !mIsInTraversal) {
        //继续跟踪
        doDie();
        return false;
    }
 
    if (!mIsDrawing) {
        destroyHardwareRenderer();
    } else {
        Log.e(TAG, "Attempting to destroy the window while drawing!\n" +
                "  window=" + this + ", title=" + mWindowAttributes.getTitle());
    }
    mHandler.sendEmptyMessage(MSG_DIE);
    return true;
}

7、ViewRootImpl.doDie

void doDie() {
    checkThread();
    if (LOCAL_LOGV) Log.v(TAG, "DIE in " + this + " of " + mSurface);
    synchronized (this) {
        if (mRemoved) {
            return;
        }
        mRemoved = true;
        if (mAdded) {
            //这里是真正移除Dialog的View
            dispatchDetachedFromWindow();
        }
 
        if (mAdded && !mFirst) {
            //硬件渲染destroy
            destroyHardwareRenderer();
 
            if (mView != null) {
                int viewVisibility = mView.getVisibility();
                boolean viewVisibilityChanged = mViewVisibility != viewVisibility;
                if (mWindowAttributesChanged || viewVisibilityChanged) {
                    // If layout params have been changed, first give them
                    // to the window manager to make sure it has the correct
                    // animation info.
                    try {
                        if ((relayoutWindow(mWindowAttributes, viewVisibility, false)
                                & WindowManagerGlobal.RELAYOUT_RES_FIRST_TIME) != 0) {
                            mWindowSession.finishDrawing(mWindow);
                        }
                    } catch (RemoteException e) {
                    }
                }
                //Surface的释放
                mSurface.release();
            }
        }
 
        mAdded = false;
    }
    //移除之前存储的变量
    WindowManagerGlobal.getInstance().doRemoveView(this);
}

保证线程安全后，做移除和释放工作

8、WindowManagerGlobal.doRemoveView

一般程序最后的工作都是释放工作，移除之前存储的变量

void doRemoveView(ViewRootImpl root) {
    synchronized (mLock) {
        final int index = mRoots.indexOf(root);
        if (index >= 0) {
            //释放工作
            mRoots.remove(index);
            mParams.remove(index);
            final View view = mViews.remove(index);
            mDyingViews.remove(view);
        }
    }
    if (HardwareRenderer.sTrimForeground && HardwareRenderer.isAvailable()) {
        doTrimForeground();
    }
}

9、ViewRootImpl.dispatchDetachedFromWindow

void dispatchDetachedFromWindow() {
    if (mView != null && mView.mAttachInfo != null) {
        mAttachInfo.mTreeObserver.dispatchOnWindowAttachedChange(false);
        //此方法会回调onDetachedFromWindow方法，会做资源的回收
        mView.dispatchDetachedFromWindow();
    }
 
    mAccessibilityInteractionConnectionManager.ensureNoConnection();
    mAccessibilityManager.removeAccessibilityStateChangeListener(
            mAccessibilityInteractionConnectionManager);
    mAccessibilityManager.removeHighTextContrastStateChangeListener(
            mHighContrastTextManager);
    removeSendWindowContentChangedCallback();
 
    destroyHardwareRenderer();
 
    setAccessibilityFocus(null, null);
 
    mView.assignParent(null);
    mView = null;
    mAttachInfo.mRootView = null;
 
    mSurface.release();
 
    if (mInputQueueCallback != null && mInputQueue != null) {
        mInputQueueCallback.onInputQueueDestroyed(mInputQueue);
        mInputQueue.dispose();
        mInputQueueCallback = null;
        mInputQueue = null;
    }
    if (mInputEventReceiver != null) {
        mInputEventReceiver.dispose();
        mInputEventReceiver = null;
    }
    try {
        //这里调用了mWindowSession的remove方法，在WindowManagerService层通过IPC机制完成真正的window删除
       mWindowSession.remove(mWindow);
    } catch (RemoteException e) {
    }
 
    // Dispose the input channel after removing the window so the Window Manager
    // doesn't interpret the input channel being closed as an abnormal termination.
    if (mInputChannel != null) {
        mInputChannel.dispose();
        mInputChannel = null;
    }
 
    mDisplayManager.unregisterDisplayListener(mDisplayListener);
 
    unscheduleTraversals();
}

到最后会和添加View的时候完成闭环，还是通过WindowSession的IPC机制去调用的，最后在WindowManagerService层通过IPC机制去实现的

总结

1. Dialog的dismiss和show形成闭环，调用的过程是相似的，只不过多了资源的释放环节

DialogFragment

DialogFragment本身继承自Fragment

public class DialogFragment extends Fragment
        implements DialogInterface.OnCancelListener, DialogInterface.OnDismissListener

在平时中，我们需要自定义WeDialogFragment，而且在正式开发中踩过的坑：

• 需要对参数进行onSaveInstanceState操作，这类操作主要是防止异步吊起DialogFragment报nullPoint的Bug
• 需要重写show()，对show做一层弹出时候的保护，这类操作主要是防止异步吊起DialogFragment报onSaveInstanceState的Bug

public class WeDialogFragment extends DialogFragment {

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        Bundle bundle = new Bundle();
        bundle.putString(BUNDLE_TITLE, title);
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setStyle(DialogFragment.STYLE_NO_TITLE, R.style.WeDialog);
        
        if (savedInstanceState != null) {
            title = savedInstanceState.getString(BUNDLE_TITLE);
        }
    }
    
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        Dialog dialog = super.onCreateDialog(savedInstanceState);
        dialog.setCanceledOnTouchOutside(true);
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        dialog.getWindow().setWindowAnimations(R.style.DialogAnimation);
        dialog.getWindow().setBackgroundDrawableResource(android.R.color.transparent);
        return dialog;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.view_fragment_dialog, container, false);
    }
    
    @Override
    public void show(FragmentManager manager, String tag) {
        if (!manager.isStateSaved()) {
            super.show(manager, tag);
        }
    }
}

然后在Activity中弹出DialogFragment

WeDialogFragment weDialogFragment = new WeDialogFragment();
weDialogFragment.show(activity.getSupportFragmentManager(),"weDialogFragment");       

一、DialogFragment的显示

1、DialogFragment.show

public void show(FragmentManager manager, String tag) {
    mDismissed = false;
    mShownByMe = true;
    FragmentTransaction ft = manager.beginTransaction();
    ft.add(this, tag);
    ft.commit();
}

show的方法其实就是对Fragment的处理，将Fragment添加到Fragment栈中

二、DialogFragment的隐藏

1、DialogFragment.dismiss

public void dismiss() {
    dismissInternal(false);
}

public void dismissAllowingStateLoss() {
    dismissInternal(true);
}

void dismissInternal(boolean allowStateLoss) {
    if (mDismissed) {
        return;
    }
    mDismissed = true;
    mShownByMe = false;
    if (mDialog != null) {
        mDialog.dismiss();
    }
    mViewDestroyed = true;
    if (mBackStackId >= 0) {
        getFragmentManager().popBackStack(mBackStackId,
                FragmentManager.POP_BACK_STACK_INCLUSIVE);
        mBackStackId = -1;
    } else {
        FragmentTransaction ft = getFragmentManager().beginTransaction();
        ft.remove(this);
        if (allowStateLoss) {
            ft.commitAllowingStateLoss();
        } else {
            ft.commit();
        }
    }
}

dismiss的方法也是对Fragment的处理，将Fragment移除到Fragment栈中

三、Dialog的创建

1、DialogFragment.onCreateDialog

@NonNull
public Dialog onCreateDialog(Bundle savedInstanceState) {
    return new Dialog(getActivity(), getTheme());
}

和创建普通的Dialog没什么区别，我们重写该方法，可以自定义弹出AlertDialog等其他自定义Dialog

四、Dialog的视图

1、DialogFragment.onActivityCreated

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    if (!mShowsDialog) {
        return;
    }

    //拿到的就是onCreateView返回值的view对象，具体可以在Fragment源码找到
    View view = getView();
    if (view != null) {
        if (view.getParent() != null) {
            throw new IllegalStateException(
                    "DialogFragment can not be attached to a container view");
        }
        //真正设置view
        mDialog.setContentView(view);
    }
    final Activity activity = getActivity();
    if (activity != null) {
        mDialog.setOwnerActivity(activity);
    }
    mDialog.setCancelable(mCancelable);
    mDialog.setOnCancelListener(this);
    mDialog.setOnDismissListener(this);
    if (savedInstanceState != null) {
        Bundle dialogState = savedInstanceState.getBundle(SAVED_DIALOG_STATE_TAG);
        if (dialogState != null) {
            mDialog.onRestoreInstanceState(dialogState);
        }
    }
}

在Activity创建的时候，Fragment的周期会回调onActivityCreated，从而对Dialog设置视图

五、Dialog的显示隐藏

Dialog显示隐藏就简单了，随着Fragment的生命周期显示和隐藏，直接看代码就行了

@Override
public void onStart() {
    super.onStart();
    if (mDialog != null) {
        mViewDestroyed = false;
        mDialog.show();
    }
}

@Override
public void onStop() {
    super.onStop();
    if (mDialog != null) {
        mDialog.hide();
    }
}

总结

DialogFragment = Fragment + Dialog，DialogFragment本身继承Fragment，Fragment只是用来依附在Activity上，可以监听Activity的生命周期，从而去通知Dialog做对应的操作，而Dialog才是我们正在显示在屏幕上的弹窗，而非一个Fragment。这里的Dialog真正显示出来的View是从onCreateView()中获取view后，在源码中调用dialog的setContentView()显示出来的