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

最新推荐文章于 2021-05-28 15:14:07 发布

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本文解决BroadcastReceiver中启动Activity出现的异常问题，需设置FLAG_ACTIVITY_NEW_TASK标志。

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 在BroadcastReceiver中启动Activity的问题

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

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

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 context.startActivity(intent);

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 可捕获异常信息:

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 android.util.AndroidRuntimeException: 

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

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 Is this really what you want?

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

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 需要给Intent设置一个flag:FLAG_ACTIVITY_NEW_TASK

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

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

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 intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

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 context.startActivity(intent);

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 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:

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 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

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

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 3 对于startActivity()方法,源码中有这么一段描述:

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

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

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

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

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

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 in its own separate task.

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 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.

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

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 如有更加深入的理解,请指点,多谢

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