Android WindowManagerService解析（５）

强烈建议看这篇文章前把前面的几篇都看看，这样理解更深刻

下面来看看Toast的显示过程

一、Toast的创建

public static Toast makeText(Context context, CharSequence text, int duration) {    Toast result = new Toast(context);    LayoutInflater inflate = (LayoutInflater)            context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);    View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null);    TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message);    tv.setText(text);    result.mNextView = v;    result.mDuration = duration;    return result;}

这里就是创建了一个Toast实例，并且得到一个需要显示的view，对应的就是Toast的mNextView。如果我们需要自定义一个view，也可以调用setView方法。

public void setView(View view) {    mNextView = view;}

二、显示过程

这个显示过程比前面要复杂了，但是原理其实是一样的，下面我们来看看。

public void show() {    // 1、在显示前mNextView必须不为空，这个mNextView就是我们需要设置的view    if (mNextView == null) {        throw new RuntimeException("setView must have been called");    }    // 2、获取一个NotificationManagerService的远程服务代理对象    INotificationManager service = getService();    String pkg = mContext.getPackageName();    // 3、TN是一个binder的跨进程对象，提供给NotificationManagerService远程服务进行回调    TN tn = mTN;    tn.mNextView = mNextView;    try {    // 4、这里维系了一个队列来显示Toast        service.enqueueToast(pkg, tn, mDuration);    } catch (RemoteException e) {        // Empty    }}

首先来看看getService方法。

static private INotificationManager getService() {    if (sService != null) {        return sService;    }    sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification"));    return sService;}

它得到的就是一个NotificationManagerService的远程代理对象。

我们来看看NotificationManagerService的远程服务的enqueueToast方法。

public void enqueueToast(String pkg, ITransientNotification callback, int duration){    if (DBG) Slog.i(TAG, "enqueueToast pkg=" + pkg + " callback=" + callback + " duration=" + duration);    if (pkg == null || callback == null) {        Slog.e(TAG, "Not doing toast. pkg=" + pkg + " callback=" + callback);        return ;    }    final boolean isSystemToast = isCallerSystem() || ("android".equals(pkg));    if (ENABLE_BLOCKED_TOASTS && !noteNotificationOp(pkg, Binder.getCallingUid())) {        if (!isSystemToast) {            Slog.e(TAG, "Suppressing toast from package " + pkg + " by user request.");            return;        }    }    synchronized (mToastQueue) {        int callingPid = Binder.getCallingPid();        long callingId = Binder.clearCallingIdentity();        try {            ToastRecord record;            int index = indexOfToastLocked(pkg, callback);            // If it's already in the queue, we update it in place, we don't            // move it to the end of the queue.            if (index >= 0) {                record = mToastQueue.get(index);                record.update(duration);            } else {                // Limit the number of toasts that any given package except the android                // package can enqueue.  Prevents DOS attacks and deals with leaks.                if (!isSystemToast) {                    int count = 0;                    final int N = mToastQueue.size();                    for (int i=0; i<N; i++) {                         final ToastRecord r = mToastQueue.get(i);                         if (r.pkg.equals(pkg)) {                             count++;                             if (count >= MAX_PACKAGE_NOTIFICATIONS) {                                 Slog.e(TAG, "Package has already posted " + count                                        + " toasts. Not showing more. Package=" + pkg);                                 return;                             }                         }                    }                }                // 可以看到将Toast封装成一个ToastRecord对象，加入到mToastQueue队列中去                record = new ToastRecord(callingPid, pkg, callback, duration);                mToastQueue.add(record);                index = mToastQueue.size() - 1;                keepProcessAliveLocked(callingPid);            }            // If it's at index 0, it's the current toast.  It doesn't matter if it's            // new or just been updated.  Call back and tell it to show itself.            // If the callback fails, this will remove it from the list, so don't            // assume that it's valid after this.            if (index == 0) {                showNextToastLocked();            }        } finally {            Binder.restoreCallingIdentity(callingId);        }    }}

上面就是将需要显示的Toast封装成一个ToastRecord一个一个的加入到mToastQueue队列中去，一个一个的调用showNextToastLocked方法进行显示。下面看看showNextToastLocked方法

private void showNextToastLocked() {    // 1、得到ToastRecord对象    ToastRecord record = mToastQueue.get(0);    while (record != null) {        if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback);        try {            // record中有一个callback，它就是前面说的TN对象，是一个跨进程的binder对象            // 这里就是调用的TN的show方法。            record.callback.show();            scheduleTimeoutLocked(record);            return;        } catch (RemoteException e) {            Slog.w(TAG, "Object died trying to show notification " + record.callback                    + " in package " + record.pkg);            // remove it from the list and let the process die            int index = mToastQueue.indexOf(record);            if (index >= 0) {                mToastQueue.remove(index);            }            keepProcessAliveLocked(record.pid);            if (mToastQueue.size() > 0) {                record = mToastQueue.get(0);            } else {                record = null;            }        }    }}

从代码中可以看到它调用的就是TN的show方法，TN类在Toast文件中。

private static class TN extends ITransientNotification.Stub {    final Runnable mShow = new Runnable() {        @Override        public void run() {        　　// 4、在mShow的Runnable中调用的是handleShow方法            handleShow();        }    };    final Runnable mHide = new Runnable() {        @Override        public void run() {            handleHide();            // Don't do this in handleHide() because it is also invoked by handleShow()            mNextView = null;        }    };　　// 1、创建WindowManager的布局属性    private final WindowManager.LayoutParams mParams = new WindowManager.LayoutParams();    final Handler mHandler = new Handler();        int mGravity;    int mX, mY;    float mHorizontalMargin;    float mVerticalMargin;    View mView;    View mNextView;    WindowManager mWM;    TN() {        // 2、对布局属性进行设置        final WindowManager.LayoutParams params = mParams;        params.height = WindowManager.LayoutParams.WRAP_CONTENT;        params.width = WindowManager.LayoutParams.WRAP_CONTENT;        params.format = PixelFormat.TRANSLUCENT;        params.windowAnimations = com.android.internal.R.style.Animation_Toast;        params.type = WindowManager.LayoutParams.TYPE_TOAST;        params.setTitle("Toast");        params.flags = WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON                | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE                | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;    }    // 3、这个就是回调的show方法    @Override    public void show() {        // 它直接往handler中放入一个mShow，mShow是Runnable对象        mHandler.post(mShow);    }    // 5、处理最终的显示    public void handleShow() {        if (mView != mNextView) {            handleHide();            mView = mNextView;            Context context = mView.getContext().getApplicationContext();            if (context == null) {                context = mView.getContext();            }            mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);            final Configuration config = mView.getContext().getResources().getConfiguration();            final int gravity = Gravity.getAbsoluteGravity(mGravity, config.getLayoutDirection());            mParams.gravity = gravity;            if ((gravity & Gravity.HORIZONTAL_GRAVITY_MASK) == Gravity.FILL_HORIZONTAL) {                mParams.horizontalWeight = 1.0f;            }            if ((gravity & Gravity.VERTICAL_GRAVITY_MASK) == Gravity.FILL_VERTICAL) {                mParams.verticalWeight = 1.0f;            }            mParams.x = mX;            mParams.y = mY;            mParams.verticalMargin = mVerticalMargin;            mParams.horizontalMargin = mHorizontalMargin;            if (mView.getParent() != null) {                if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this);                mWM.removeView(mView);            }            if (localLOGV) Log.v(TAG, "ADD! " + mView + " in " + this);            mWM.addView(mView, mParams);            trySendAccessibilityEvent();        }    }}

从上面我们可以看到，它最终还是调用的WindowManager的addView方法。看来UI显示是永远也绕不过WindowManagerService，这里我们可以看到，虽然我们提供了这么多UI的显示窗口，但最终的实现都是一样，都是有WindowManager来处理的。