自定義View——背景知識

  1. Activity
    • 作用：負責(zé)生命周期管理與事件處理，每個Activity組合了一個Window，實際視圖控制是交由Winodw管理ui排版。是為了滿足多窗口管理和傻瓜式視圖管理的需要而誕生的。
    • 起源：在Activity中的onCreate()方法中會調(diào)用setContentView()加載自定義視圖，實際調(diào)用的是Window的setContentView方法
    • 相關(guān)源碼： 
      android/app/Activity.java
public void setContentView(@LayoutRes int layoutResID) {
    //調(diào)用mWindow.setContentView()
    getWindow().setContentView(layoutResID);
    initWindowDecorActionBar();
}

      android/app/Activity.java
final void attach(... ...){
   ... ...
    //實例化mWindow
   mWindow = new PhoneWindow(this, window, activityConfigCallback);
    //實現(xiàn)window的接口，鍵盤觸摸 ui策略等
   mWindow.setWindowControllerCallback(this);
   mWindow.setCallback(this);
   mWindow.setOnWindowDismissedCallback(this);
   ... ...
}
  2. Window
    • 作用：唯一實現(xiàn)類PhoneWindow，創(chuàng)建了頂層視圖DecorView，DecorView作為父布局用來加載Activity中setContentView()方法傳入的layoutRes。是為了管理ui排版，視圖控制而誕生的。
    • 相關(guān)源碼： 
      com/android/internal/policy/PhoneWindow.java
@Override
public void setContentView(int layoutResID) {
    if (mContentParent == null) {
        //創(chuàng)建DecorView，并實例化DecorView布局內(nèi)的ViewGroup控件mContentParent
        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 {
        //將mContentParent作為父控件，加載layoutResID
        mLayoutInflater.inflate(layoutResID, mContentParent);
    }
   ... ...
}

      com/android/internal/policy/PhoneWindow.java
private void installDecor() {
    ... ...
    if (mDecor == null) {
        //創(chuàng)建DecorView
        mDecor = generateDecor(-1);
       ... ...
    }
    ... ...
    if (mContentParent == null) {
        //實例化mContentParent
       mContentParent = generateLayout(mDecor);
        ... ...
    }
}

      com/android/internal/policy/PhoneWindow.java
protected DecorView generateDecor(int featureId) {
    ... ...
    //創(chuàng)建DecorView
    return new DecorView(context, featureId, this, getAttributes());
}

      com/android/internal/policy/PhoneWindow.java
public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
protected ViewGroup generateLayout(DecorView decor) {
    ... ...
    int layoutResource;
    if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
        layoutResource = R.layout.screen_swipe_dismiss;
        ... ...
    } 
    ... ...
    else {
       layoutResource = R.layout.screen_simple;
    }
    ... ...
    //加載DecorView布局
    mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
    //從DecorView中獲取id為content的控件
   ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
    ... ...
    //將contentParent返回
    return contentParent;
}

      android/view/Window.java
public <T extends View> T findViewById(@IdRes int id) {
    //返回DecorView中給定id的視圖控件
    return getDecorView().findViewById(id);
}

      frameworks/base/core/res/res/layout/screen_simple.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:fitsSystemWindows="true"
   android:orientation="vertical">
   <ViewStub android:id="@+id/action_mode_bar_stub"
       android:inflatedId="@+id/action_mode_bar"
       android:layout="@layout/action_mode_bar"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:theme="?attr/actionBarTheme" />

   <FrameLayout
       android:id="@android:id/content"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:foregroundInsidePadding="false"
       android:foregroundGravity="fill_horizontal|top"
       android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>
  3. DecorView
    • 作用：繼承自FrameLayout，是Android視圖樹的根視圖，View層的事件都會先經(jīng)過DecorView，再分發(fā)到下面的View
    • 相關(guān)源碼： 
      com/android/internal/policy/DecorView.java
void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
    mDecorCaptionView = createDecorCaptionView(inflater);
    //加載PhoneWindow生成的layoutResource
    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 {
       //添加到DecorView中
        addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
    }
    mContentRoot = (ViewGroup) root;
}
  4. WindowManager
    • 作用：在Activity生命周期onResume之后，綁定DecorView與ViewRootImpl。
    • 相關(guān)源碼： 
      android/app/ActivityThread.java
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
        String reason) {
       ... ...
    //執(zhí)行activity的onResume方法
    final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
    ... ...
       final Activity a = r.activity;
       if (r.window == null && !a.mFinished && willBeVisible) {
        //獲取activity的window實例
       r.window = r.activity.getWindow();
        //獲取window中實例化的DecorView
       View decor = r.window.getDecorView();
       decor.setVisibility(View.INVISIBLE);
        //獲取windowManager,獲取的是WindowManager的子類，WindowManagerImpl
       ViewManager wm = a.getWindowManager();
       WindowManager.LayoutParams l = r.window.getAttributes();
       a.mDecor = decor;
       if (a.mVisibleFromClient) {
           if (!a.mWindowAdded) {
               a.mWindowAdded = true;
                //windowManager調(diào)用addView添加DecorView
               wm.addView(decor, l);
           }
            ... ...
       }
   }
    ... ...
}

      android/view/WindowManagerImpl.java
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}

      android/view/WindowManagerGlobal.java
public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {
    ViewRootImpl root;
    //實例化ViewRootImpl
    root = new ViewRootImpl(view.getContext(), display);
    //保存decorView對象
    mViews.add(view);
    //保存viewRootImpl對象
    mRoots.add(root);
    //保存decorView的layout params
    mParams.add(wparams);
    try {
        //綁定ViewRootImpl與DecorView
        root.setView(view, wparams, panelParentView);
    }... ...
}
  5. ViewRoot(實際實現(xiàn)類是android.view.ViewRootImpl)
    • 作用
      1. 連接DecorView與WindowManager，也可以說是Window與DecorView的紐帶
      2. 通過DecorView完成View的三大流程繪制
      3. 用責(zé)任鏈模式，向DecorView分發(fā)用戶的InputEvent事件
    • 注意：在Activity.onResume()之后，ViewRootImpl.setView中將DecorView傳入，并在之后執(zhí)行requestLayout()通過DecorView遞歸執(zhí)行View的三大流程，所以View的三大流程都是在Activity.onResume之后。
    • 相關(guān)源碼： 
      android/view/ViewRootImpl.java
final IWindowSession mWindowSession;

public ViewRootImpl(Context context, Display display) {
    //WindowManagerGlobal獲取IWindowSession
    mWindowSession = WindowManagerGlobal.getWindowSession();
}

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
    synchronized (this) {
        if (mView == null) {
            //這個mView就是DecorView，view的三大繪制流程均是通過mView來遞歸的
            mView = view;
            ... ...
            //view的三大繪制流程
            requestLayout();
            //創(chuàng)建InputChannel
            mInputChannel = new InputChannel();
            //wms根據(jù)當(dāng)前的window創(chuàng)建了SocketPair用于跨進程通信，并對傳入的mInputChannel進行了注冊
            //此后ViewRootImpl中的mInputChannel就指向了正確的InputChannel
            //client端與server端就能進行雙向通信了
            res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                           getHostVisibility(), mDisplay.getDisplayId(), mTmpFrame,
                       mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                       mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, mInputChannel,
                       mTempInsets);
            //創(chuàng)建WindowInputEventReceiver，處理事件分發(fā)
            mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
                          Looper.myLooper());
            //組裝InputStage責(zé)任鏈
            mSyntheticInputStage = new SyntheticInputStage();
            InputStage viewPostImeStage = new ViewPostImeInputStage(mSyntheticInputStage);
            InputStage nativePostImeStage = new NativePostImeInputStage(viewPostImeStage,
                        "aq:native-post-ime:" + counterSuffix);
            InputStage earlyPostImeStage = new EarlyPostImeInputStage(nativePostImeStage);
            InputStage imeStage = new ImeInputStage(earlyPostImeStage,
                        "aq:ime:" + counterSuffix);
            InputStage viewPreImeStage = new ViewPreImeInputStage(imeStage);
            InputStage nativePreImeStage = new NativePreImeInputStage(viewPreImeStage,
                        "aq:native-pre-ime:" + counterSuffix);
            mFirstInputStage = nativePreImeStage;
            mFirstPostImeInputStage = earlyPostImeStage;
        }
    }
}
      • View的三大繪制流程入口
      android/view/ViewRootImpl.java
public void requestLayout() {
    if (!mHandlingLayoutInLayoutRequest) {
        checkThread();
        mLayoutRequested = true;
        //這里執(zhí)行view的繪制流程
        scheduleTraversals();
    }
}

final class TraversalRunnable implements Runnable {
   @Override
   public void run() {
       doTraversal();
   }
}

final TraversalRunnable mTraversalRunnable = new TraversalRunnable();

void scheduleTraversals() {
   if (!mTraversalScheduled) {
        ... ...
       mChoreographer.postCallback(
           Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
        ... ...
   }
}

void doTraversal() {
   if (mTraversalScheduled) {
       ... ...
       performTraversals();
        ... ...
   }
}

private void performTraversals() {
    ... ...
    //measure流程
    performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
    //layout流程
    performLayout(lp, mWidth, mHeight);
    //draw流程
    performDraw();
}

private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
   try {
        //執(zhí)行DecorView的mesaure流程
       mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
   } finally {
       Trace.traceEnd(Trace.TRACE_TAG_VIEW);
   }
}

private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
            int desiredWindowHeight) {
    final View host = mView;
    try {
        //執(zhí)行DecorView的layout流程
       host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
    }
}

private void performDraw() {
    ... ...
    try {
       boolean canUseAsync = draw(fullRedrawNeeded);
    }
    ... ...
}

private boolean draw(boolean fullRedrawNeeded) {
    ... ...
    if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset,
        scalingRequired, dirty, surfaceInsets)) {
       return false;
   }
    ... ...
}

private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,
        boolean scalingRequired, Rect dirty, Rect surfaceInsets) {
    ... ...
    //執(zhí)行DecorView的draw流程
    mView.draw(canvas);
    ... ...
}
  6. 綜上
    1. 創(chuàng)建DecorView的流程：
      • Activity在attach時，會創(chuàng)建PhoneWindow實例mWindow;
      • Activity在onCreate中調(diào)用setContentView方法時，會間接調(diào)用mWindow.setContentView;
      • PhoneWindow在setContentView中會創(chuàng)建DecorView的實例，并將Activity傳入的布局加載到DecorView中id為content的mContentParent中;
      • DecorView是android視圖樹的根節(jié)點，最底層的View，在PhoneWindow創(chuàng)建布局時generateLayout會根據(jù)不同類型的主題創(chuàng)建布局，其中會有一個id為content的ViewGroup，Activity中傳入的布局文件就是以content為父布局;
    2. 建立DecorView與WindowManager的聯(lián)系并最終繪制顯示的流程：
      • ActivityThread在調(diào)用handleResumeActivity，會執(zhí)行Activity的onResume方法，隨后，會創(chuàng)建ViewRootImpl的實例，獲取Activity的Window實例，并獲取Window中的DecorView實例，使用WindowManager，將ViewRootImpl與DecorView綁定;
      • ViewRootImpl獲取到DecorView的實例后，會持有該引用，并分步調(diào)用mView的measure,layout,draw方法。
    3. 當(dāng)InputManager監(jiān)控到硬件層面的輸入事件時，會通知ViewRootImpl對輸入事件進行底層分發(fā)(具體細節(jié)查看View的事件分發(fā)機制)
      • 創(chuàng)建InputChannel，并通過Binder在SystemServer進程中完成InputChannel的注冊。
      • 創(chuàng)建WindowInputEventReceiver來處理事件分發(fā)。
      • 組裝InputStage責(zé)任鏈，負責(zé)不同InputEvent事件的處理。
  7. 其他要點
    • View ---getLeft() getTop() getRight() getBottom()返回的是View 相對與ViewGroup的左上右下距離
    • MotionEvent---getRawX() getRawY()返回的是觸摸點相對于屏幕的x/y距離 getX() getY()返回的是觸摸點相對于自身控件的x/y距離
  8. 系列文章
    1. View的背景知識
    2. View的測量流程
    3. View的布局流程
    4. View的繪制背景知識
    5. View的繪制流程
    6. View的三大繪制流程總結(jié)
    7. View的事件分發(fā)機制
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