Android事件分发流程

1 起源

Android中Activity的setContentView会调用getWindow().setContentView()方法,getWindow返回的是一个Window对象,在Android中的唯一实现是PhoneWindow:

private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
        //创建DecorView
           ** mDecor = generateDecor(-1)**;
           ...
        } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
        //ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
           ** mContentParent = generateLayout(mDecor);**
        }
        ...
    }

在PhoneWindow中会安装DecorView,找到DecorView中的ContentParent,然后把我们传进来布局添加到ContentParent中.(setContentView的父布局)

在ActivityThread的handleResumeActivity()方法中

//mVisibleFromClient activity中属性  默认为true
if (a.mVisibleFromClient) {
                if (!a.mWindowAdded) {
                    a.mWindowAdded = true;
                    wm.addView(decor, l);
                } else {
                    a.onWindowAttributesChanged(l);
                }
            }

windowManager在Android中的实现是WindowManagerImpl.

   @Override
    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        //   private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance(); 单例
        mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow,
                mContext.getUserId());
    }

WindowManagerGlobal的addView,在这里创建了ViewRootImpl

public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow, int userId) {
      ...
        ViewRootImpl root;
        View panelParentView = null;
            root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);

            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);

            // do this last because it fires off messages to start doing things
            try {
                root.setView(view, wparams, panelParentView, userId);
            } catch (RuntimeException e) {
            ...
                throw e;
            }
        }
    }

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,
            int userId) {
            
            ...
             mView = view;
               requestLayout();
               //接收事件
                mInputEventReceiver = new WindowInputEventReceiver(inputChannel,
                            Looper.myLooper());
            
            }

final class WindowInputEventReceiver extends InputEventReceiver {
        public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
            super(inputChannel, looper);
        }

        @Override
        public void onInputEvent(InputEvent event) {
        //事件分发的起点
            Trace.traceBegin(Trace.TRACE_TAG_VIEW, "processInputEventForCompatibility");
            List<InputEvent> processedEvents;
            try {
                processedEvents =
                    mInputCompatProcessor.processInputEventForCompatibility(event);
            } finally {
                Trace.traceEnd(Trace.TRACE_TAG_VIEW);
            }
            if (processedEvents != null) {
                if (processedEvents.isEmpty()) {
                    // InputEvent consumed by mInputCompatProcessor
                    finishInputEvent(event, true);
                } else {
                    for (int i = 0; i < processedEvents.size(); i++) {
                        enqueueInputEvent(
                                processedEvents.get(i), this,
                               QueuedInputEvent.FLAG_MODIFIED_FOR_COMPATIBILITY, true);
                    }
                }
            } else {
                enqueueInputEvent(event, this, 0, true);
            }
        }
}
void enqueueInputEvent(InputEvent event,
            InputEventReceiver receiver, int flags, boolean processImmediately) {
        QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
        if (processImmediately) {
            doProcessInputEvents();
        } else {
        //也会调用到doProcessInputEvents()
            scheduleProcessInputEvents();
        }
    }
 void doProcessInputEvents() {
     ...
           deliverInputEvent(q);
        ...
    }
private void deliverInputEvent(QueuedInputEvent q) {
 
            InputStage stage;
            if (q.shouldSendToSynthesizer()) {
                stage = mSyntheticInputStage;
            } else {
                stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
            }
            if (stage != null) {
                handleWindowFocusChanged();
                stage.deliver(q);
            } else {
                finishInputEvent(q);
            }
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
    }

在onInputEvent中会调用enqueueInputEvent(),scheduleProcessInputEvents最后也会doProcessInputEvents()
InputStage 一个处理处理Input Event的责任链基类;在ViewRootImpl的setView中有设置

 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;

stage.deliver(q);中事件会传递到ViewPostImeInputStage的onProcess方法
我们重点关注下:ViewPostImeInputStage

        public ViewPostImeInputStage(InputStage next) {
            super(next);
        }

        @Override
        protected int onProcess(QueuedInputEvent q) {
            if (q.mEvent instanceof KeyEvent) {//按键事件
                return processKeyEvent(q);
            } else {
                final int source = q.mEvent.getSource();
                if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {//触摸事件
                    return processPointerEvent(q);
                } else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
                    return processTrackballEvent(q);
                } else {
                    return processGenericMotionEvent(q);
                }
            }
        }}

private int processPointerEvent(QueuedInputEvent q) {

        final MotionEvent event = (MotionEvent)q.mEvent;
        boolean handled = mView.dispatchPointerEvent(event);
        return handled ? FINISH_HANDLED : FORW     }

这里的mView就是DecorView,是在调用setView时候赋值的,由此事件传递到了DecorView

View的方法
@UnsupportedAppUsage

public final boolean dispatchPointerEvent(MotionEvent event) {
    if (event.isTouchEvent()) {
        return dispatchTouchEvent(event);
    } else {
        return dispatchGenericMotionEvent(event);
    }
}
//DecorView的方法
    @Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//cb就是activity 在Activity的attach中设置mWindow.setCallback(this);
    final Window.Callback cb = mWindow.getCallback();
    return cb != null && !mWindow.isDestroyed() && mFeatureId < 0
            ? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);
}
//activity的方法
  public boolean dispatchTouchEvent(MotionEvent ev) {
    if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        onUserInteraction();
    }
    if (getWindow().superDispatchTouchEvent(ev)) {
        return true;
    }
    return onTouchEvent(ev);
}
//事件重新到了DecorView 
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
    return mDecor.superDispatchTouchEvent(event);
}
//DecorView public class DecorView extends FrameLayout
 public boolean superDispatchTouchEvent(MotionEvent event) {
    return super.dispatchTouchEvent(event);
}

DecorView是FrameLayout的子类,事件传递到了我们熟悉的ViewGroup