关于FLAG_ACTIVITY_CLEAR_TOP

　

flag_activity_clear_top

flag_activity_clear_top :如果设置，并且要启动的activity已经在当前的任务中，那么在该activity之上的activity都会关闭，并且intent会传递给老的activity（现在在栈顶）

例如，假设一个任务包含四个activity:A，B,C,D,假设D中启动B并且带有次标志，则 C和D都会结束，并且B会收到intet，现在的栈变成了A,B

在上面的例子中，当前运行的B要么在他的onNewIntent方法中接受这个Intent，或者结束掉已经存在的实例并且重启一个，这依赖与B的启动模式，如果是确实的"multiple(即standard)",那么结束掉实例并重启一个，其他启动模式下将会调用他的onNewIntent

示例：

假设从MainActivity启动ActivityA，从ActivityA中启动ActivityB，在从ActivityB中启动ActivityA且A的启动模式为standard,其他都为默认，

1、不设置，我们看一下按照上面这个顺序启动后的堆栈：

ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)
  Main stack:
    TaskRecord{4240b790 #60 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 #4: ActivityRecord{413e6990 u0 com.leaves.ipanel/.ActivityA}
        Intent { act=com.leaves.ipanel.ActivityA cmp=com.leaves.ipanel/.ActivityA }
        ProcessRecord{41344a80 13731:com.leaves.ipanel/u0a10061}
      Hist #3: ActivityRecord{413c8430 u0 com.leaves.ipanel/.ActivityB}
        Intent { act=com.leaves.ipanel.ActivityB cmp=com.leaves.ipanel/.ActivityB }
        ProcessRecord{41344a80 13731:com.leaves.ipanel/u0a10061}
      Hist #2: ActivityRecord{4133b580 u0 com.leaves.ipanel/.ActivityA}
        Intent { act=com.leaves.ipanel.ActivityA cmp=com.leaves.ipanel/.ActivityA }
        ProcessRecord{41344a80 13731:com.leaves.ipanel/u0a10061}
      Hist #1: ActivityRecord{4132a3d0 u0 com.leaves.ipanel/.MainActivity}
        Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity }
        ProcessRecord{41344a80 13731: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}

可以看到这个是我们正常结果。

2、接下来我们在ActivityB启动ActivityA的时候携带FLAG_ACTIVITY_CLEAR_TOP ，wield了比较，我们先启动到AcitvityB，看一下堆栈：

ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)
  Main stack:
    TaskRecord{42f58468 #61 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{41388e48 u0 com.leaves.ipanel/.ActivityB}
        Intent { act=com.leaves.ipanel.ActivityB cmp=com.leaves.ipanel/.ActivityB }
        ProcessRecord{41343690 13827:com.leaves.ipanel/u0a10061}
      Hist #2: ActivityRecord{4133b580 u0 com.leaves.ipanel/.ActivityA}
        Intent { act=com.leaves.ipanel.ActivityA cmp=com.leaves.ipanel/.ActivityA }
        ProcessRecord{41343690 13827:com.leaves.ipanel/u0a10061}
      Hist #1: ActivityRecord{4132a3d0 u0 com.leaves.ipanel/.MainActivity}
        Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity }
        ProcessRecord{41343690 13827: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}

可见最上面一个task里面有三个activity，我们在从ActivityB中启动ActivityA,

	public void onClick(View v) {
		// TODO Auto-generated method stub
		Log.i(TAG, "--onClick--task id = " + getCurrentTaskId());	
		
		Intent intent = new Intent("com.leaves.ipanel.ActivityA");  
		//Intent intent = new Intent("com.example.testactivitylaunchflag2.ActivityAA");
		intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP );
		//intent.addFlags(Intent.flag_activity_new_task);
		startActivity(intent); 
	}

启动后的堆栈：

ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)
  Main stack:
    TaskRecord{42f58468 #61 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 #2: ActivityRecord{413b5728 u0 com.leaves.ipanel/.ActivityA}
        Intent { act=com.leaves.ipanel.ActivityA flg=0x4000000 cmp=com.leaves.ipanel/.ActivityA }
        ProcessRecord{41343690 13827:com.leaves.ipanel/u0a10061}
      Hist #1: ActivityRecord{4132a3d0 u0 com.leaves.ipanel/.MainActivity}
        Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity }
        ProcessRecord{41343690 13827: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}

可以看到刚才ActivityA上面的ActivityB已经结束掉了，自己也结束掉了然后重新创建了一个，从哪里可以看出来是重新创建了呢？可以看打印出来的ActivityRecord不一样了。这是由于ActivityA的启动模式为standard,即允许有多个实例，我们把ActivityA的启动模式改为singleTask,在跑一下上面的测试流程：

启动到ActivityB后：

ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)
  Main stack:
    TaskRecord{414100e8 #62 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{413c8430 u0 com.leaves.ipanel/.ActivityB}
        Intent { act=com.leaves.ipanel.ActivityB cmp=com.leaves.ipanel/.ActivityB }
        ProcessRecord{41344a80 13948:com.leaves.ipanel/u0a10061}
      Hist #2: ActivityRecord{4133b580 u0 com.leaves.ipanel/.ActivityA}
        Intent { act=com.leaves.ipanel.ActivityA cmp=com.leaves.ipanel/.ActivityA }
        ProcessRecord{41344a80 13948:com.leaves.ipanel/u0a10061}
      Hist #1: ActivityRecord{4132a3d0 u0 com.leaves.ipanel/.MainActivity}
        Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity }
        ProcessRecord{41344a80 13948: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}

再启动ActivityA:

ACTIVITY MANAGER ACTIVITIES (dumpsys activity activities)
  Main stack:
    TaskRecord{414100e8 #62 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 #2: ActivityRecord{4133b580 u0 com.leaves.ipanel/.ActivityA}
        Intent { act=com.leaves.ipanel.ActivityA cmp=com.leaves.ipanel/.ActivityA }
        ProcessRecord{41344a80 13948:com.leaves.ipanel/u0a10061}
      Hist #1: ActivityRecord{4132a3d0 u0 com.leaves.ipanel/.MainActivity}
        Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.leaves.ipanel/.MainActivity }
        ProcessRecord{41344a80 13948: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}

可以看出，ActiivtyB还是结束掉了，但ActivityA没有重新创建，我们可以看到ActivityA的ActivityRecord是一样的。这个时候调用的是ActivityA的onNewIntent,而没有重新onCreate创建一个，我们从log也可以看出来

I/ActivityB(14013): --onpause--task id = 63
I/ActivityA(14013): --onNewIntent--task id = 63
I/ActivityA(14013): --onRestart--task id = 63
I/ActivityA(14013): --onStart--task id = 63
I/ActivityA(14013): --onResume--task id = 63
D/hwcomposer(  111): fb1 realy close!
D/hwcomposer(  111): fb1 open! I/ActivityB(14013): --onStop--task id = 63
I/ActivityB(14013): --onDestroy--task id = 63

从Log可以看出调用了ActivityA的onNewIntent，而ActivityB调用了onDestroy.

使用其他的启动模式，都会调用onNewInten，而在standard模式下则会new 重新new一个

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