View的生命周期和Activity生命周期的执行顺序

前言

了解了View的生命周期和Activity的生命周期能够让我们更好的理解View的工作原理。

代码

我们先写一个自定义View，然后打印出它的生命周期方法

public class MyTextView extends TextView {    private static final String TAG = "MyTextView";    public MyTextView(Context context) {        super(context);    }    public MyTextView(Context context, @Nullable AttributeSet attrs) {        super(context, attrs);    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        Log.d(TAG, "onMeasure: ");        super.onMeasure(widthMeasureSpec, heightMeasureSpec);    }    @Override    protected void onDraw(Canvas canvas) {        Log.d(TAG, "onDraw: ");        super.onDraw(canvas);    }    @Override    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {        Log.d(TAG, "onLayout: ");        super.onLayout(changed, left, top, right, bottom);    }    @Override    protected void onAttachedToWindow() {        super.onAttachedToWindow();        Log.d(TAG, "onAttachedToWindow: ");    }    @Override    protected void onSizeChanged(int w, int h, int oldw, int oldh) {        super.onSizeChanged(w, h, oldw, oldh);        Log.d(TAG, "onSizeChanged: ");    }}

然后在Activity的布局中引用这个View,然后我们在Activity中打印出生命周期方法

public class MainActivity extends Activity {    private static final String TAG = "MyTextView";    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        Log.d(TAG, "onCreate: ");    }    @Override    protected void onStart() {        Log.d(TAG, "onStart: ");        super.onStart();    }    @Override    protected void onResume() {        Log.d(TAG, "onResume: ");        super.onResume();    }    @Override    public void onWindowFocusChanged(boolean hasFocus) {        Log.d(TAG, "onWindowFocusChanged: ");        super.onWindowFocusChanged(hasFocus);    }}

最终结果如下

下面在记录一下触摸事件产生的过程。

触摸事件被系统处理后，会传到ViewRootImpl中进行进一步处理，

final class WindowInputEventReceiver extends InputEventReceiver {        public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {            super(inputChannel, looper);        }        //接受事件        @Override        public void onInputEvent(InputEvent event) {            enqueueInputEvent(event, this, 0, true);        }        @Override        public void onBatchedInputEventPending() {            if (mUnbufferedInputDispatch) {                super.onBatchedInputEventPending();            } else {                scheduleConsumeBatchedInput();            }        }        @Override        public void dispose() {            unscheduleConsumeBatchedInput();            super.dispose();        }    }

 void enqueueInputEvent(InputEvent event,            InputEventReceiver receiver, int flags, boolean processImmediately) {        QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);        // Always enqueue the input event in order, regardless of its time stamp.        // We do this because the application or the IME may inject key events        // in response to touch events and we want to ensure that the injected keys        // are processed in the order they were received and we cannot trust that2        // the time stamp of injected events are monotonic.        QueuedInputEvent last = mPendingInputEventTail;        if (last == null) {            mPendingInputEventHead = q;            mPendingInputEventTail = q;        } else {            last.mNext = q;            mPendingInputEventTail = q;        }        mPendingInputEventCount += 1;        Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,                mPendingInputEventCount);        if (processImmediately) {            doProcessInputEvents();        } else {            scheduleProcessInputEvents();        }    }

 void doProcessInputEvents() {        // Deliver all pending input events in the queue.        while (mPendingInputEventHead != null) {            QueuedInputEvent q = mPendingInputEventHead;            mPendingInputEventHead = q.mNext;            if (mPendingInputEventHead == null) {                mPendingInputEventTail = null;            }            q.mNext = null;            mPendingInputEventCount -= 1;            Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,                    mPendingInputEventCount);            deliverInputEvent(q);        }        // We are done processing all input events that we can process right now        // so we can clear the pending flag immediately.        if (mProcessInputEventsScheduled) {            mProcessInputEventsScheduled = false;            mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);        }    }

 private void deliverInputEvent(QueuedInputEvent q) {5687        Trace.asyncTraceBegin(Trace.TRACE_TAG_VIEW, "deliverInputEvent",                q.mEvent.getSequenceNumber());        if (mInputEventConsistencyVerifier != null) {            mInputEventConsistencyVerifier.onInputEvent(q.mEvent, 0);        }        InputStage stage;        if (q.shouldSendToSynthesizer()) {            stage = mSyntheticInputStage;        } else {            stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;        }        if (stage != null) {            stage.deliver(q);        } else {           finishInputEvent(q);        }    }

接下来我们看看InputStage
在ViewRootImpl的setView方法中，进行了InputStage的初始化

  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);

  final class ViewPostImeInputStage extends InputStage {        public ViewPostImeInputStage(InputStage next) {            super(next);        }        @Override        protected int onProcess(QueuedInputEvent q) {            if (q.mEvent instanceof KeyEvent) {                return processKeyEvent(q);            } else {                // If delivering a new non-key event, make sure the window is                // now allowed to start updating.                handleDispatchDoneAnimating();                final int source = q.mEvent.getSource();                if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {                    return processPointerEvent(q);                } else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {                    return processTrackballEvent(q);                } else {                    return processGenericMotionEvent(q);                }            }        }

我们看看processPointerEvent这个方法。

 private int processPointerEvent(QueuedInputEvent q) {            final MotionEvent event = (MotionEvent)q.mEvent;            mAttachInfo.mUnbufferedDispatchRequested = false;            boolean handled = mView.dispatchPointerEvent(event);            if (mAttachInfo.mUnbufferedDispatchRequested && !mUnbufferedInputDispatch) {                mUnbufferedInputDispatch = true;                if (mConsumeBatchedInputScheduled) {                    scheduleConsumeBatchedInputImmediately();                }            }            return handled ? FINISH_HANDLED : FORWARD;        }

这里调用了mView.dispatchPointerEvent这个方法。
mView是DecorView，我们并没有在DecorView里发现这个方法，于是我们在View中去找。

  public final boolean dispatchPointerEvent(MotionEvent event) {        if (event.isTouchEvent()) {            return dispatchTouchEvent(event);        } else {            return dispatchGenericMotionEvent(event);        }    }

接下来调用了DecorView的dispatchTouchEvent方法，

 @Override        public boolean dispatchTouchEvent(MotionEvent ev) {            final Callback cb = getCallback();            return cb != null && !isDestroyed() && mFeatureId < 0 ? cb.dispatchTouchEvent(ev)                    : super.dispatchTouchEvent(ev);        }

这里我们看cb.dispathTouchEvent这个方法,cb是Window.Callback对象，而Activity实现了这个接口，所以调用了Activity中的

 public boolean dispatchTouchEvent(MotionEvent ev) {        if (ev.getAction() == MotionEvent.ACTION_DOWN) {            onUserInteraction();        }        if (getWindow().superDispatchTouchEvent(ev)) {            return true;        }        return onTouchEvent(ev);    }

又把事件传到了Window中，我们知道这个Window是PhoneWindow,

 @Overridepublic boolean superDispatchTouchEvent(MotionEvent event) {        return mDecor.superDispatchTouchEvent(event);    }

又到了DecorView的superDispatchTouchEvent方法，

public boolean superDispatchTouchEvent(MotionEvent event) {            return super.dispatchTouchEvent(event);        }

到这里就调用了ViewGroup的dispatchTouchEvent开始分发事件。