java - 检查 Activity 是否在 Service 中启动

Question

我有一个服务正在做一些后台工作，然后我需要启动一个 Activity 来显示服务处理的一些结果。但是有可能从服务中多次启动该 Activity 。现在，我只想在该 Activity 尚未激活时才启动它。

这有什么可能性以及如何做到这一点？如果您不介意，示例代码会很好。

谢谢!!

Answer 1

您应该在 androidManifest.xml 文件中将 Activity 的 launchMode 更改为 singleTask。

此属性的默认值为standard，它允许运行任意数量的实例。

"singleTask" and "singleInstance" activities can only begin a task. They are always at the root of the activity stack. Moreover, the device can hold only one instance of the activity at a time — only one such task. [...]

The "singleTask" and "singleInstance" modes also differ from each other in only one respect: A "singleTask" activity allows other activities to be part of its task. It's always at the root of its task, but other activities (necessarily "standard" and "singleTop" activities) can be launched into that task. A "singleInstance" activity, on the other hand, permits no other activities to be part of its task. It's the only activity in the task. If it starts another activity, that activity is assigned to a different task — as if FLAG_ACTIVITY_NEW_TASK was in the intent.

查看 Android Developers' Guide以获得更详细的解释(引述也来自那里)

<activity android:name=".activity.YourActivity" 
    android:launchMode="singleTask"
    android:alwaysRetainTaskState="true"
    android:clearTaskOnLaunch="false" 
    android:finishOnTaskLaunch="false">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.DEFAULT" />
    </intent-filter>
</activity>