moveTasktoBack 把当前任务放入后台

http://blog.csdn.net/newcman/article/details/7801400

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用Activity.moveTaskToBack()把当前任务放入后台，详细看注释：

/**
 * Move the task containing this activity to the back of the activity
 * stack.  The activity's order within the task is unchanged.
 * 把该activity所在的task移到栈底，顺序不变
 * @param nonRoot If false then this only works if the activity is the root
 *                of a task; if true it will work for any activity in
 *                a task.
 * nonRoot：false：当该activity是root activity才有用，true：所有的activity都有用
 * @return If the task was moved (or it was already at the
 *         back) true is returned, else false.
 */
public boolean moveTaskToBack(boolean nonRoot) {
    try {
        return ActivityManagerNative.getDefault().moveActivityTaskToBack(
                <span style="color:#ff6666;">mToken</span>, nonRoot);
    } catch (RemoteException e) {
        // Empty
    }
    return false;
}

上边的mToken是IBinder类型，代表该Activity与ActivityManagerService进行IPC通信（进程间通信），直接看ActivityManagerService源码，如下

/**
 * Moves an activity, and all of the other activities within the same task, to the bottom
 * of the history stack.  The activity's order within the task is unchanged.
 *  把该activity所在的task移到栈底，顺序不变
 * @param token A reference to the activity we wish to move 保存activity的引用
 * @param nonRoot If false then this only works if the activity is the root
 *                of a task; if true it will work for any activity in a task.
 * nonRoot：false：当该activity是root activity才有用，true：所有的activity都有用
 * @return Returns true if the move completed, false if not.
 */
public boolean moveActivityTaskToBack(IBinder token, boolean nonRoot) {
    synchronized(this) {
        final long origId = Binder.clearCallingIdentity();
        int taskId = getTaskForActivityLocked(token, !nonRoot);
        if (taskId >= 0) {
            return mMainStack.moveTaskToBackLocked(taskId, null);
        }
        Binder.restoreCallingIdentity(origId);
    }
    return false;
}

 

getTaskForActivityLocked：

    <pre class="java" name="code"> /**
     *  //找出token（activity）所在的栈
     * @param token 在服务端为ActivityRecord，在客户端为Activity
     * @param onlyRoot true 则只对root Activity有效，false对所有的Activity都有效
     * @return
     */
    int getTaskForActivityLocked(IBinder token, boolean onlyRoot) {
        final int N = mMainStack.mHistory.size();
        TaskRecord lastTask = null;
        for (int i=0; i<N; i++) {
            ActivityRecord r = (ActivityRecord)mMainStack.mHistory.get(i);
            if (r == token) {
                if (!onlyRoot || lastTask != r.task) {//不是root Activity时返回第一次匹配的task，否则查找root Activity对应的task
                    return r.task.taskId;
                }
                return -1;
            }
            lastTask = r.task;
        }

        return -1;
    }
</pre><pre class="java" name="code"><pre></pre>
<p>mMainStack为ActivityStack，moveTaskToBackLocked如下：</p>
<pre class="html" name="code">    /**
     * Worker method for rearranging history stack.  Implements the function of moving all
     * activities for a specific task (gathering them if disjoint) into a single group at the
     * bottom of the stack.
     * 把特定的task移到栈底，并且保持顺序不变
     * If a watcher is installed, the action is preflighted and the watcher has an opportunity
     * to premeptively cancel the move.
     *
     * @param task The taskId to collect and move to the bottom.
     * @return Returns true if the move completed, false if not.
     */
    final boolean moveTaskToBackLocked(int task, ActivityRecord reason) {
</pre><pre class="html" name="code">    ....</pre><pre class="html" name="code"> //移动到底部
        while (pos < N) {
            ActivityRecord r = mHistory.get(pos);
            if (localLOGV) Slog.v(
                TAG, "At " + pos + " ckp " + r.task + ": " + r);
            if (r.task.taskId == task) {
                if (localLOGV) Slog.v(TAG, "Removing and adding at " + (N-1));
                if (DEBUG_ADD_REMOVE) {
                    RuntimeException here = new RuntimeException("here");
                    here.fillInStackTrace();
                    Slog.i(TAG, "Removing and adding activity " + r + " to stack at "
                            + bottom, here);
                }
                mHistory.remove(pos);
                mHistory.add(bottom, r);
                moved.add(r);
                bottom++;
            }
            pos++;
        }}</pre><pre class="html" name="code">   ....</pre><pre class="html" name="code">}
</pre>
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