BroadcastReceiver 启动activity（在activity之外启动一个activity）

**

 * 在BroadcastReceiver中启动Activity的问题

 *

 * 如果在BroadcastReceiver的onReceive()方法中如下启动一个Activity

 * Intent intent=new Intent(context,AnotherActivity.class);

 * context.startActivity(intent);

 * 可捕获异常信息:

 * android.util.AndroidRuntimeException:

 * Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK flag.

 * Is this really what you want?

 * 它说明:在Activity的context(上下文环境)之外调用startActivity()方法时

 * 需要给Intent设置一个flag:FLAG_ACTIVITY_NEW_TASK

 *

 * 所以在BroadcastReceiver的onReceive()方法中启动Activity应写为:

 * Intent intent=new Intent(context,AnotherActivity.class);

 * intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

 * context.startActivity(intent);

 *

 *

 * 之前描述了问题的现象和解决办法,现在试着解释一下原因:

 * 1 在普通情况下,必须要有前一个Activity的Context,才能启动后一个Activity

 * 2 但是在BroadcastReceiver里面是没有Activity的Context的

 * 3 对于startActivity()方法,源码中有这么一段描述:

 *   Note that if this method is being called from outside of an

 *   {@link android.app.Activity} Context, then the Intent must include

 *   the {@link Intent#FLAG_ACTIVITY_NEW_TASK} launch flag.  This is because,

 *   without being started from an existing Activity, there is no existing

 *   task in which to place the new activity and thus it needs to be placed

 *   in its own separate task.

 *   说白了就是如果不加这个flag就没有一个Task来存放新启动的Activity.

 *  

 * 4 其实该flag和设置Activity的LaunchMode为SingleTask的效果是一样的

 *

 *

 * 如有更加深入的理解,请指点,多谢

 *

 */