Dialog中的一个函数的源码分析

这个函数是从Dialog.java里找到的：

/**
     * @return The activity associated with this dialog, or null if there is no assocaited activity.
     */
    private ComponentName getAssociatedActivity() {
        Activity activity = mOwnerActivity;
        Context context = getContext();
        while (activity == null && context != null) {
            if (context instanceof Activity) {
                activity = (Activity) context;  // found it!
            } else {
                context = (context instanceof ContextWrapper) ?
                        ((ContextWrapper) context).getBaseContext() : // unwrap one level
                        null;                                         // done
            }
        }
        return activity == null ? null : activity.getComponentName();
    }

 函数的作用是找到与Dialog关联的Activity的ComponentName,这个复杂的判断逻辑吸引了我，所以把它拿出来分析分析。

 

这个函数为什么要分析Activity和Context的区分呢，我想可能是在Activity里new这个dialog的时候，有的人是用this来代替this.getApplicationContext()吧，猜测呵呵。如果是的话那么确实会有很大区别。

 

当然更主要的是Activity是继承自Context的才导致了这个复杂的判断，呵呵

 

从下面的函数的注释来看，判断这个Dialog的所有者即Activity是为了万一要用到声音控制：

 

/**
     * Sets the Activity that owns this dialog. An example use: This Dialog will
     * use the suggested volume control stream of the Activity.
     *
     * @param activity The Activity that owns this dialog.
     */
    public final void setOwnerActivity(Activity activity) {
        mOwnerActivity = activity;
       
        getWindow().setVolumeControlStream(mOwnerActivity.getVolumeControlStream());
    }

 

下面这个也能验证我的一个猜测，即Dialog未必都是从Activity里制造出来的，所以才会有返回值是NUll的情况

 

/**
     * Returns the Activity that owns this Dialog. For example, if
     * {@link Activity#showDialog(int)} is used to show this Dialog, that
     * Activity will be the owner (by default). Depending on how this dialog was
     * created, this may return null.
     *
     * @return The Activity that owns this Dialog.
     */
    public final Activity getOwnerActivity() {
        return mOwnerActivity;
    }