Android中FLAG_ACTIVITY_CLEAR_TASK的作用
2014-10-13 22:31
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FLAG_ACTIVITY_CLEAR_TASK :如果在调用Context.startActivity时传递这个标记,将会导致任何用来放置该activity的已经存在的task里面的已经存在的activity先清空,然后该activity再在该task中启动,也就是说,这个新启动的activity变为了这个空tas的根activity.所有老的activity都结束掉。该标志必须和FLAG_ACTIVITY_NEW_TASK一起使用。
示例:
我们有三个activity:MainActivity、ActivityA、ActivityB. 依次从MainActivity中启动ActivityA,从ActivityA中启动ActivityB.
首先我们所有的都使用缺省的,也即没有设置taskAffinity、launchMode,启动activity时Intent也不带标记,我们看一下启动B之后的堆栈:
[plain] view
plaincopyprint?
ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)
Main stack:
TaskRecord{4199dd68 #56 A com.leaves.ipanel U 0}
Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity }
Hist #3: ActivityRecord{4140fdf8 u0 com.leaves.ipanel/.ActivityB}
Intent { act=com.leaves.ipanel.ActivityB cmp=com.leaves.ipanel/.ActivityB }
ProcessRecord{41517e80 13350:com.leaves.ipanel/u0a10061}
Hist #2: ActivityRecord{413ff7e8 u0 com.leaves.ipanel/.ActivityA}
Intent { act=com.leaves.ipanel.ActivityA cmp=com.leaves.ipanel/.ActivityA }
ProcessRecord{41517e80 13350:com.leaves.ipanel/u0a10061}
Hist #1: ActivityRecord{413f8b28 u0 com.leaves.ipanel/.MainActivity}
Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity }
ProcessRecord{41517e80 13350:com.leaves.ipanel/u0a10061}
TaskRecord{41350f60 #2 A com.android.launcher U 0}
Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10600000 cmp=com.android.launcher/com.android.launcher2.Launcher }
Hist #0: ActivityRecord{41616790 u0 com.android.launcher/com.android.launcher2.Launcher}
Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000000 cmp=com.android.launcher/com.android.launcher2.Launcher }
ProcessRecord{41615818 628:com.android.launcher/1000}
可以看到三者在同一个task中,且都存在。
接下来我们在启动ActivityB时添加FLAG_ACTIVITY_CLEAR_TASK和FLAG_ACTIVITY_NEW_TASK
[java] view
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public void onClick(View v) {
// TODO Auto-generated method stub
Log.i(TAG, "--onClick--task id = " + getCurrentTaskId());
Intent intent = new Intent("com.leaves.ipanel.ActivityB");
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
}
再看下启动ActivityB之后的堆栈:
[plain] view
plaincopyprint?
ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)
Main stack:
TaskRecord{4245bd10 #57 A com.leaves.ipanel U 0}
Intent { act=com.leaves.ipanel.ActivityB flg=0x10008000 cmp=com.leaves.ipanel/.ActivityB }
Hist #1: ActivityRecord{413f8b28 u0 com.leaves.ipanel/.ActivityB}
Intent { act=com.leaves.ipanel.ActivityB flg=0x10008000 cmp=com.leaves.ipanel/.ActivityB }
ProcessRecord{41413010 13441:com.leaves.ipanel/u0a10061}
TaskRecord{41350f60 #2 A com.android.launcher U 0}
Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10600000 cmp=com.android.launcher/com.android.launcher2.Launcher }
Hist #0: ActivityRecord{41616790 u0 com.android.launcher/com.android.launcher2.Launcher}
Intent { act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000000 cmp=com.android.launcher/com.android.launcher2.Launcher }
ProcessRecord{41615818 628:com.android.launcher/1000}
可以看到,MainActivity和ActivityA都被结束掉了,原因就是因为该task用来装载ActivityB,而启动时又设置了FLAG_ACTIVITY_CLEAR_TASK和FLAG_ACTIVITY_NEW_TASK
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