android view 的创建解析,拦截view的创建并进行操作(一)

由于要做视差动画,需要获取每一个的view并对view进行操作,所以研究了一下view 的创建。

首先我们创建一个Activity让他继承AppCompatActivity 进入AppCompatActivity会看到在onCreate()方法中有一段代码叫final AppCompatDelegate delegate = getDelegate(); activity的生命周期都交给了这个类来管理了 我们点进去找到这个他会通过你不同的版本创建不同的AppCompatDelegate实现类 但是所有的实现类都基自AppCompatDelegateImplV9,先看看AppCompatDelegateImplV9是继承LayoutInflaterFactory这个接口的,这是本篇文章的中心,下面会解释

    private static AppCompatDelegate create(Context context, Window window,
            AppCompatCallback callback) {
        final int sdk = Build.VERSION.SDK_INT;
        if (BuildCompat.isAtLeastN()) {
            return new AppCompatDelegateImplN(context, window, callback);
        } else if (sdk >= 23) {
            return new AppCompatDelegateImplV23(context, window, callback);
        } else if (sdk >= 14) {
            return new AppCompatDelegateImplV14(context, window, callback);
        } else if (sdk >= 11) {
            return new AppCompatDelegateImplV11(context, window, callback);
        } else {
            return new AppCompatDelegateImplV9(context, window, callback);
        }
    }

走到setContentView(int resId)

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

他会一直调用直到这个方法中inflate()的createViewFromTag(root, name, inflaterContext, attrs); 进入这个方法


 public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
        synchronized (mConstructorArgs) {
        ..............................
        ..............................
        ..............................

                if (TAG_MERGE.equals(name)) {
                    if (root == null || !attachToRoot) {
                        throw new InflateException(" can be used only with a valid "
                                + "ViewGroup root and attachToRoot=true");
                    }

                    rInflate(parser, root, inflaterContext, attrs, false);
                } else {
                    // Temp is the root view that was found in the xml
                    
                    final View temp = createViewFromTag(root, name, inflaterContext, attrs);
                    ..........................

              }

   ......................
        }
    }

这样就进到了view 的创建关键代码 这里会通过多重判断来保证view不会为空的情况 主要难理解的是这个view = mFactory2.onCreateView(parent, name, context, attrs); 点进去发现是个接口,现在回到AppCompatActivity这个类中找到 delegate.installViewFactory();这行代码 他调用的是AppCompatDelegateImplV9 installViewFactory();

 View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
            boolean ignoreThemeAttr) {
        if (name.equals("view")) {
            name = attrs.getAttributeValue(null, "class");
        }

        // Apply a theme wrapper, if allowed and one is specified.
        if (!ignoreThemeAttr) {
            final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
            final int themeResId = ta.getResourceId(0, 0);
            if (themeResId != 0) {
                context = new ContextThemeWrapper(context, themeResId);
            }
            ta.recycle();
        }
        
        if (name.equals(TAG_1995)) {
            // Let's party like it's 1995!
            return new BlinkLayout(context, attrs);
        }

        try {
            View view;
            if (mFactory2 != null) {
                view = mFactory2.onCreateView(parent, name, context, attrs);
            } else if (mFactory != null) {
                view = mFactory.onCreateView(name, context, attrs);
            } else {
                view = null;
            }

            if (view == null && mPrivateFactory != null) {
                view = mPrivateFactory.onCreateView(parent, name, context, attrs);
            }

            if (view == null) {
                final Object lastContext = mConstructorArgs[0];
                mConstructorArgs[0] = context;
                try {
                    if (-1 == name.indexOf('.')) {
                        view = onCreateView(parent, name, attrs);
                    } else {
                        view = createView(name, null, attrs);
                    }
                } finally {
                    mConstructorArgs[0] = lastContext;
                }
            }

            return view;
        } catch (InflateException e) {
            throw e;

        } catch (ClassNotFoundException e) {
            final InflateException ie = new InflateException(attrs.getPositionDescription()
                    + ": Error inflating class " + name, e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;

        } catch (Exception e) {
            final InflateException ie = new InflateException(attrs.getPositionDescription()
                    + ": Error inflating class " + name, e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        }
    }
 @Override
    public void installViewFactory() {
        LayoutInflater layoutInflater = LayoutInflater.from(mContext);
        if (layoutInflater.getFactory() == null) {
        //刚刚开始肯定是空这,就是初始化的地方 LayoutInflaterCompat 这就是Factory的管理类
            LayoutInflaterCompat.setFactory(layoutInflater, this);
        } else {
            if (!(LayoutInflaterCompat.getFactory(layoutInflater)
                    instanceof AppCompatDelegateImplV9)) {
                Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"
                        + " so we can not install AppCompat's");
            }
        }
    }
    

最后就会调用到LayoutInflater的setFactory中 这样factory就有值了而且factory就是我们的AppCompatDelegateImplV9 继续回到上面只看一小段 mFactory2.onCreateView(parent, name, context, attrs);他会调用AppCompatDelegateImplV9的onCreateView方法

createViewFromTag(){
     View view;
            if (mFactory2 != null) {
                view = mFactory2.onCreateView(parent, name, context, attrs);
            } else if (mFactory != null) {
                view = mFactory.onCreateView(name, context, attrs);
            } else {
                view = null;
            }
}

//以下是V9的方法
  public final View onCreateView(View parent, String name,
            Context context, AttributeSet attrs) {
        // First let the Activity's Factory try and inflate the view
        final View view = callActivityOnCreateView(parent, name, context, attrs);
        if (view != null) {
            return view;
        }

        // If the Factory didn't handle it, let our createView() method try
        return createView(parent, name, context, attrs
        }
        
        
        
        
        //最终会到这个方法中
        
            @Override
    public View createView(View parent, final String name, @NonNull Context context,
            @NonNull AttributeSet attrs) {
        final boolean isPre21 = Build.VERSION.SDK_INT < 21;

        if (mAppCompatViewInflater == null) {
            mAppCompatViewInflater = new AppCompatViewInflater();
        }

        // We only want the View to inherit its context if we're running pre-v21
        final boolean inheritContext = isPre21 && shouldInheritContext((ViewParent) parent);

        return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,
                isPre21, /* Only read android:theme pre-L (L+ handles this anyway) */
                true, /* Read read app:theme as a fallback at all times for legacy reasons */
                VectorEnabledTintResources.shouldBeUsed() /* Only tint wrap the context if enabled */
        );
    }
        

看到这个类 AppCompatViewInflater 这就是创建View的类来看里面的代码 就是通过这样我们就拿到大部分的view了

 public final View createView(View parent, final String name, @NonNull Context context,
            @NonNull AttributeSet attrs, boolean inheritContext,
            boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
        final Context originalContext = context;

        // We can emulate Lollipop's android:theme attribute propagating down the view hierarchy
        // by using the parent's context
        if (inheritContext && parent != null) {
            context = parent.getContext();
        }
        if (readAndroidTheme || readAppTheme) {
            // We then apply the theme on the context, if specified
            context = themifyContext(context, attrs, readAndroidTheme, readAppTheme);
        }
        if (wrapContext) {
            context = TintContextWrapper.wrap(context);
        }

        View view = null;

        // We need to 'inject' our tint aware Views in place of the standard framework versions
        switch (name) {
            case "TextView":
                view = new AppCompatTextView(context, attrs);
                break;
            case "ImageView":
                view = new AppCompatImageView(context, attrs);
                break;
            case "Button":
                view = new AppCompatButton(context, attrs);
                break;
            case "EditText":
                view = new AppCompatEditText(context, attrs);
                break;
            case "Spinner":
                view = new AppCompatSpinner(context, attrs);
                break;
            case "ImageButton":
                view = new AppCompatImageButton(context, attrs);
                break;
            case "CheckBox":
                view = new AppCompatCheckBox(context, attrs);
                break;
            case "RadioButton":
                view = new AppCompatRadioButton(context, attrs);
                break;
            case "CheckedTextView":
                view = new AppCompatCheckedTextView(context, attrs);
                break;
            case "AutoCompleteTextView":
                view = new AppCompatAutoCompleteTextView(context, attrs);
                break;
            case "MultiAutoCompleteTextView":
                view = new AppCompatMultiAutoCompleteTextView(context, attrs);
                break;
            case "RatingBar":
                view = new AppCompatRatingBar(context, attrs);
                break;
            case "SeekBar":
                view = new AppCompatSeekBar(context, attrs);
                break;
        }

        if (view == null && originalContext != context) {
            // If the original context does not equal our themed context, then we need to manually
            // inflate it using the name so that android:theme takes effect.
            view = createViewFromTag(context, name, attrs);
        }

        if (view != null) {
            // If we have created a view, check it's android:onClick
            checkOnClickListener(view, attrs);
        }

        return view;
    }

下一张我会通过这个理论来拦截所有的view的创建做我们自己的事情

你可能感兴趣的:(android view 的创建解析,拦截view的创建并进行操作(一))