FLAG_ACTIVITY_CLEAR_TASK :如果在調(diào)用Context.startActivity時傳遞這個標(biāo)記，將會導(dǎo)致任何用來放置該activity的已經(jīng)存在的task里面的已經(jīng)存在

的activity先清空，然后該activity再在該task中啟動，也就是說，這個新啟動的activity變?yōu)榱诉@個空tas的根activity.所有老的activity都結(jié)束掉。

該標(biāo)志必須和FLAG_ACTIVITY_NEW_TASK一起使用。

示例：

我們有三個activity:MainActivity、ActivityA、ActivityB. 依次從MainActivity中啟動ActivityA，從ActivityA中啟動ActivityB.

首先我們所有的都使用缺省的，也即沒有設(shè)置taskAffinity、launchMode，啟動activity時Intent也不帶標(biāo)記，我們看一下啟動B之后的堆棧：

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個task中，且都存在。

接下來我們在啟動ActivityB時添加FLAG_ACTIVITY_CLEAR_TASK和FLAG_ACTIVITY_NEW_TASK

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); } 再看下啟動ActivityB之后的堆棧：

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都被結(jié)束掉了，原因就是因為該task用來裝載ActivityB，而啟動時又設(shè)置了FLAG_ACTIVITY_CLEAR_TASK和FLAG_ACTIVITY_NEW_TASK

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