android2.2源码初探

由于代码中涉及到UI的布局，不得已看android源码。

源码系android-8即2.2

从调试环境看最初调用NativeStart.java中的main函数，经过底层的若干次调用，途经ActivityThread.java中的main函数调用，代码如下：

[code]     [code]public static final void main(String[] args) {

SamplingProfilerIntegration.start();

Process.setArgV0("<pre-initialized>");

Looper.prepareMainLooper();

ActivityThread thread = new ActivityThread();

thread.attach(false);

Looper.loop();

if (Process.supportsProcesses()) {

throw new RuntimeException("Main thread loop unexpectedly exited");

}

thread.detach();

String name = (thread.mInitialApplication != null)

? thread.mInitialApplication.getPackageName()

: "<unknown>";

Slog.i(TAG, "Main thread of " + name + " is now exiting");

}

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这儿应是程序的起点，Looper.loop()展示的为相关的消息处理机制。使得程序不像普通的main函数一样立刻就结束了。

Looper.java中loop()就是一个消息循环，代码如下：

[code]
[code]/**

*  Run the message queue in this thread. Be sure to call

* {@link #quit()} to end the loop.

*/

public static final void loop() {

Looper me = myLooper();

MessageQueue queue = me.mQueue;

while (true) {

Message msg = queue.next(); // might block

//if (!me.mRun) {

//    break;

//}

if (msg != null) {

if (msg.target == null) {

// No target is a magic identifier for the quit message.

return;

}

if (me.mLogging!= null) me.mLogging.println(

">>>>> Dispatching to " + msg.target + " "

+ msg.callback + ": " + msg.what

);

msg.target.dispatchMessage(msg);

if (me.mLogging!= null) me.mLogging.println(

"<<<<< Finished to    " + msg.target + " "

+ msg.callback);

msg.recycle();

}

 }

}

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顺便把怎样结束消息循环的代码也贴出来，方便对照消息开始的地方。

[code]
[code]public void quit() {

Message msg = Message.obtain();

// NOTE: By enqueueing directly into the message queue, the

// message is left with a null target.  This is how we know it is

// a quit message.

mQueue.enqueueMessage(msg, 0);

}

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接着看Handler.java

[code]
[code]/**

* Handle system messages here.

*/

public void dispatchMessage(Message msg) {

if (msg.callback != null) {

handleCallback(msg);

 } else {

if (mCallback != null) {

if (mCallback.handleMessage(msg)) {

return;

}

}

handleMessage(msg);

 }

}

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handleMessage（）我们在写消息处理的时候经常用到，看ViewRoot.java中，

[code]
[code]@Override

public void handleMessage(Message msg) {

switch (msg.what) {

case View.AttachInfo.INVALIDATE_MSG:

((View) msg.obj).invalidate();

break;

case View.AttachInfo.INVALIDATE_RECT_MSG:

final View.AttachInfo.InvalidateInfo info = (View.AttachInfo.InvalidateInfo) msg.obj;

info.target.invalidate(info.left, info.top, info.right, info.bottom);

info.release();

break;

case DO_TRAVERSAL:

if (mProfile) {

Debug.startMethodTracing("ViewRoot");

}

performTraversals();

if (mProfile) {

Debug.stopMethodTracing();

mProfile = false;

}

break;

case FINISHED_EVENT:

handleFinishedEvent(msg.arg1, msg.arg2 != 0);

break;

case DISPATCH_KEY:

if (LOCAL_LOGV) Log.v(

"ViewRoot", "Dispatching key "

+ msg.obj + " to " + mView);

deliverKeyEvent((KeyEvent)msg.obj, true);

break;

case DISPATCH_POINTER: {

MotionEvent event = (MotionEvent)msg.obj;

boolean callWhenDone = msg.arg1 != 0;

if (event == null) {

    try {

        long timeBeforeGettingEvents;

        if (MEASURE_LATENCY) {

  timeBeforeGettingEvents = System.nanoTime();

}

        event = sWindowSession.getPendingPointerMove(mWindow);

        if (MEASURE_LATENCY && event != null) {

  lt.sample("9 Client got events      ", System.nanoTime() - event.getEventTimeNano());

  lt.sample("8 Client getting events  ", timeBeforeGettingEvents - event.getEventTimeNano());

}

} catch (RemoteException e) {

}

    callWhenDone = false;

}

if (event != null && mTranslator != null) {

    mTranslator.translateEventInScreenToAppWindow(event);

}

try {

    boolean handled;

    if (mView != null && mAdded && event != null) {

        // enter touch mode on the down

        boolean isDown = event.getAction() == MotionEvent.ACTION_DOWN;

        if (isDown) {

  ensureTouchMode(true);

}

        if(Config.LOGV) {

  captureMotionLog("captureDispatchPointer", event);

}

        if (mCurScrollY != 0) {

  event.offsetLocation(0, mCurScrollY);

}

        if (MEASURE_LATENCY) {

  lt.sample("A Dispatching TouchEvents", System.nanoTime() - event.getEventTimeNano());

}

        handled = mView.dispatchTouchEvent(event);

        if (MEASURE_LATENCY) {

  lt.sample("B Dispatched TouchEvents ", System.nanoTime() - event.getEventTimeNano());

}

        if (!handled && isDown) {

  int edgeSlop = mViewConfiguration.getScaledEdgeSlop();

  final int edgeFlags = event.getEdgeFlags();

  int direction = View.FOCUS_UP;

  int x = (int)event.getX();

  int y = (int)event.getY();

  final int[] deltas = new int[2];

  if ((edgeFlags & MotionEvent.EDGE_TOP) != 0) {

      direction = View.FOCUS_DOWN;

      if ((edgeFlags & MotionEvent.EDGE_LEFT) != 0) {

deltas[0] = edgeSlop;

x += edgeSlop;

} else if ((edgeFlags & MotionEvent.EDGE_RIGHT) != 0) {

deltas[0] = -edgeSlop;

x -= edgeSlop;

}

} else if ((edgeFlags & MotionEvent.EDGE_BOTTOM) != 0) {

      direction = View.FOCUS_UP;

      if ((edgeFlags & MotionEvent.EDGE_LEFT) != 0) {

deltas[0] = edgeSlop;

x += edgeSlop;

} else if ((edgeFlags & MotionEvent.EDGE_RIGHT) != 0) {

deltas[0] = -edgeSlop;

x -= edgeSlop;

}

} else if ((edgeFlags & MotionEvent.EDGE_LEFT) != 0) {

      direction = View.FOCUS_RIGHT;

} else if ((edgeFlags & MotionEvent.EDGE_RIGHT) != 0) {

      direction = View.FOCUS_LEFT;

}

  if (edgeFlags != 0 && mView instanceof ViewGroup) {

      View nearest = FocusFinder.getInstance().findNearestTouchable(

    ((ViewGroup) mView), x, y, direction, deltas);

      if (nearest != null) {

event.offsetLocation(deltas[0], deltas[1]);

event.setEdgeFlags(0);

mView.dispatchTouchEvent(event);

}

}

}

}

} finally {

    if (callWhenDone) {

        try {

  sWindowSession.finishKey(mWindow);

} catch (RemoteException e) {

}

}

    if (event != null) {

        event.recycle();

}

    if (LOCAL_LOGV || WATCH_POINTER) Log.i(TAG, "Done dispatching!");

    // Let the exception fall through -- the looper will catch

    // it and take care of the bad app for us.

}

} break;

case DISPATCH_TRACKBALL:

deliverTrackballEvent((MotionEvent)msg.obj, msg.arg1 != 0);

break;

case DISPATCH_APP_VISIBILITY:

handleAppVisibility(msg.arg1 != 0);

break;

case DISPATCH_GET_NEW_SURFACE:

handleGetNewSurface();

break;

case RESIZED:

ResizedInfo ri = (ResizedInfo)msg.obj;

if (mWinFrame.width() == msg.arg1 && mWinFrame.height() == msg.arg2

        && mPendingContentInsets.equals(ri.coveredInsets)

        && mPendingVisibleInsets.equals(ri.visibleInsets)

        && ((ResizedInfo)msg.obj).newConfig == null) {

    break;

}

// fall through...

case RESIZED_REPORT:

if (mAdded) {

    Configuration config = ((ResizedInfo)msg.obj).newConfig;

    if (config != null) {

        updateConfiguration(config, false);

}

    mWinFrame.left = 0;

    mWinFrame.right = msg.arg1;

    mWinFrame.top = 0;

    mWinFrame.bottom = msg.arg2;

    mPendingContentInsets.set(((ResizedInfo)msg.obj).coveredInsets);

    mPendingVisibleInsets.set(((ResizedInfo)msg.obj).visibleInsets);

    if (msg.what == RESIZED_REPORT) {

        mReportNextDraw = true;

}

    if (mView != null) {

        forceLayout(mView);

}

    requestLayout();

}

break;

case WINDOW_FOCUS_CHANGED: {

if (mAdded) {

    boolean hasWindowFocus = msg.arg1 != 0;

    mAttachInfo.mHasWindowFocus = hasWindowFocus;

    if (hasWindowFocus) {

        boolean inTouchMode = msg.arg2 != 0;

        ensureTouchModeLocally(inTouchMode);

        if (mGlWanted) {

  checkEglErrors();

  // we lost the gl context, so recreate it.

  if (mGlWanted && !mUseGL) {

      initializeGL();

      if (mGlCanvas != null) {

float appScale = mAttachInfo.mApplicationScale;

mGlCanvas.setViewport(

        (int) (mWidth * appScale + 0.5f),

        (int) (mHeight * appScale + 0.5f));

}

}

}

}

    mLastWasImTarget = WindowManager.LayoutParams

  .mayUseInputMethod(mWindowAttributes.flags);

    InputMethodManager imm = InputMethodManager.peekInstance();

    if (mView != null) {

        if (hasWindowFocus && imm != null && mLastWasImTarget) {

  imm.startGettingWindowFocus(mView);

}

        mAttachInfo.mKeyDispatchState.reset();

        mView.dispatchWindowFocusChanged(hasWindowFocus);

}

    // Note: must be done after the focus change callbacks,

    // so all of the view state is set up correctly.

    if (hasWindowFocus) {

        if (imm != null && mLastWasImTarget) {

  imm.onWindowFocus(mView, mView.findFocus(),

mWindowAttributes.softInputMode,

!mHasHadWindowFocus, mWindowAttributes.flags);

}

        // Clear the forward bit.  We can just do this directly, since

        // the window manager doesn't care about it.

        mWindowAttributes.softInputMode &=

      ~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;

        ((WindowManager.LayoutParams)mView.getLayoutParams())

      .softInputMode &=

~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;

        mHasHadWindowFocus = true;

}

    if (hasWindowFocus && mView != null) {

        sendAccessibilityEvents();

}

}

} break;

case DIE:

doDie();

break;

case DISPATCH_KEY_FROM_IME: {

if (LOCAL_LOGV) Log.v(

"ViewRoot", "Dispatching key "

    + msg.obj + " from IME to " + mView);

KeyEvent event = (KeyEvent)msg.obj;

if ((event.getFlags()&KeyEvent.FLAG_FROM_SYSTEM) != 0) {

    // The IME is trying to say this event is from the

    // system!  Bad bad bad!

    event = KeyEvent.changeFlags(event,

  event.getFlags()&~KeyEvent.FLAG_FROM_SYSTEM);

}

deliverKeyEventToViewHierarchy((KeyEvent)msg.obj, false);

} break;

case FINISH_INPUT_CONNECTION: {

InputMethodManager imm = InputMethodManager.peekInstance();

if (imm != null) {

    imm.reportFinishInputConnection((InputConnection)msg.obj);

}

} break;

case CHECK_FOCUS: {

InputMethodManager imm = InputMethodManager.peekInstance();

if (imm != null) {

    imm.checkFocus();

}

} break;

case CLOSE_SYSTEM_DIALOGS: {

if (mView != null) {

    mView.onCloseSystemDialogs((String)msg.obj);

}

} break;

}

 }

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