Toast源码浅析

1.Toast的用法

Toast.makeText(this, "Toast", Toast.LENGTH_SHORT).show();

2.makeText入手

    public static Toast makeText(Context context, CharSequence text, @Duration 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;    }

只是加载了一个布局。接下来我们看show方法

3.Toast#show

    public void show() {        if (mNextView == null) {            throw new RuntimeException("setView must have been called");        }        INotificationManager service = getService();        String pkg = mContext.getOpPackageName();        TN tn = mTN;        tn.mNextView = mNextView;        try {            service.enqueueToast(pkg, tn, mDuration);        } catch (RemoteException e) {            // Empty        }    }

• 如果mNextView==null，抛出异常

• 获取INotificationManager

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

• 将toast插入队列。

* 这里的INotificationManager，是在启动的时候加载到ServiceManager的mCache里的，关于如何加载的这里略过，对应的服务端实现在NotificationManagerService里 *

4.NotificationManagerService里的enqueueToast方法。

    @Override    public void enqueueToast(String pkg, ITransientNotification callback, int duration)    {        //省略代码        final boolean isSystemToast = isCallerSystem() || ("android".equals(pkg));        //省略代码        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;                                }                            }                        }                    }                    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);            }        }    }

代码略长，听我慢慢道来、

• 算出当前Toast在ToastQueue中的索引，

• 如果>=0,怎说明已经在队列中，更新时间即可

• ! >= 0的情况下

  • 如果不是系统Toast，就判断当前包名下，队列中有多少个toast，>=50，直接返回，并更新index

  • 将其包装一下加入队列

• 设置该Toast所在的进程为前台进程

• 如果index为0，显示。

5.NotificationManagerService#showNextToastLocked

    void showNextToastLocked() {        ToastRecord record = mToastQueue.get(0);        while (record != null) {            if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback);            try {                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;                }            }        }    }

代码比较简单，调用ToastRecore.callback的show方法去显示，并且发一个延时消息。

    private void scheduleTimeoutLocked(ToastRecord r)    {        mHandler.removeCallbacksAndMessages(r);        Message m = Message.obtain(mHandler, MESSAGE_TIMEOUT, r);        long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;        mHandler.sendMessageDelayed(m, delay);    }

那么，这里的record的callback的show方法是什么呢。record是我们从队列中取出来的，他的初始化方法在enqueueToast方法中。

record = new ToastRecord(callingPid, pkg, callback, duration);

而这里的callback是enqueueToast的参数，也就是说，是我们在Toast中出传入的。Toast中相关代码如下

service.enqueueToast(pkg, tn, mDuration);

这里的tn是在toast初始化的时候初始化的。因此，将会掉TN的show方法。

6.TN#show

        @Override        public void show() {            if (localLOGV) Log.v(TAG, "SHOW: " + this);            mHandler.post(mShow);        }

        final Runnable mShow = new Runnable() {            @Override            public void run() {                handleShow();            }        };

会看到，最后就会调用handleShow方法。

7.TN#handleShow

    public void handleShow() {        if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView                + " mNextView=" + mNextView);        if (mView != mNextView) {            // remove the old view if necessary            handleHide();            mView = mNextView;            Context context = mView.getContext().getApplicationContext();            String packageName = mView.getContext().getOpPackageName();            if (context == null) {                context = mView.getContext();            }            mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);            // We can resolve the Gravity here by using the Locale for getting            // the layout direction            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;            mParams.packageName = packageName;            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();        }    }

上面的代码很简单，就是设置View的参数，并通过WindowManager添加显示。

8.NotificationManagerService#cancelToastLocked

这个方法中，调用TN的hide方法隐藏当前Toast，并从列表中移除，将下一个Toast所在的进程挂到前台，并显示。

hide方法中，只是调用WindowManager的removeView移除。

大家自己去看源码去吧。