讲讲Android的launchMode,taskAffinity,以及Intent Flags

站在巨人的肩膀上

理解 + 总结

结论:

如果Activity的launchMode是standard或singleTop,那么taskAffinity设置无效,该Activity会跟随启动它的Activity一致的affinity

准备条件:
    ActivityA: android:launchMode="standard"  android:taskAffinity="hello.world"
    ActivityB: android:launchMode="standard"  android:taskAffinity="hello.everyone"
    ActivityB: android:launchMode="singleTop" android:taskAffinity="hello.everybody"

步骤:
    打开ActivityA -> startActivity到ActivityB -> startActivity到ActivityC           
结果:(adb shell dumpsys activity)
    Stack #40: type=standard mode=fullscreen
    
        Running activities (most recent first):
            TaskRecord{fae42ac #403 A=hello.world U=0 StackId=40 sz=3}
                Run #2: ActivityRecord{d2989ab u0 com.example.hurshi.app_a/.AppA_ActivityC t403}
                Run #1: ActivityRecord{62cf49f u0 com.example.hurshi.app_a/.AppA_ActivityB t403}
                Run #0: ActivityRecord{93b3122 u0 com.example.hurshi.app_a/.AppA_ActivityA t403}

由上述实验可知,虽然ActivityB设置了taskAffinity为hello.everyone,但它还是放在和ActivityA一致的hello.world的task中,说明在上述情况中,设置taskAffinity无效.ActivityC同理.

结论:

taskAffinity并不是task的唯一编号,允许不同task拥有相同的taskAffinity

准备条件:
    ActivityA: android:launchMode="singleInstance" android:taskAffinity="hello.world"
    ActivityB: android:launchMode="singleInstance" android:taskAffinity="hello.world"
    
步骤: 
    打开ActivityA -> startActivity到ActivityB 
    
结果:
    Stack #12: type=standard mode=fullscreen
        Running activities (most recent first):
            TaskRecord{783509b #348 A=hello.world U=0 StackId=12 sz=1}
                Run #0: ActivityRecord{eeea074 u0 com.example.hurshi.app_a/.AppA_ActivityB t348}
                
    Stack #11: type=standard mode=fullscreen
        Running activities (most recent first):
            TaskRecord{85abc38 #347 A=hello.world U=0 StackId=11 sz=1}
            Run #0: ActivityRecord{4f6d2db u0 com.example.hurshi.app_a/.AppA_ActivityA t347}

由上述ActivityA,ActivityB可以看出,他们的taskAffinity是一致的,但是它们的stackId是不一致的,由此可知:taskAffinity并不是task的唯一编号,允许不同task拥有相同的taskAffinity

结论:

当luanchMode为singleTask或者设置Intent.FLAG_ACTIVITY_NEW_TASK的时候,系统会寻找新的task来存放目标Activity,寻找是依据目标Activity的taskAffinity属性进行匹配,找不到就新建task然后放入.

如果只设置了singleTask或者Intent.FLAG_ACTIVITY_NEW_TASK,没有设置taskAffinity,那么该Activity会沿用Application的taskAffinity,而Application的默认taskAffinity是包名

准备条件:
    Application: android:taskAffinity="com.application"
    ActivityA: android:launchMode="standard"       android:taskAffinity="hello.world"
    ActivityB: android:launchMode="singleTask" android:taskAffinity="hello.everyone"

步骤:
    打开ActivityA -> startActivity到ActivityB          
结果:
    Stack #38: type=standard mode=fullscreen
         Running activities (most recent first):
            TaskRecord{7ff1d1c #401 A=com.application U=0 StackId=38 sz=1}
                Run #0: ActivityRecord{ecb9efb u0 com.example.hurshi.app_a/.AppA_ActivityB t401}

    Stack #37: type=standard mode=fullscreen
        Running activities (most recent first):
            TaskRecord{2261d25 #400 A=hello.world U=0 StackId=37 sz=1}
                Run #0: ActivityRecord{4b36f0f u0 com.example.hurshi.app_a/.AppA_ActivityA t400}

结论:

在如上结论的基础上,新的Activity设置singleTask后,并不一定会添加到已存在的相同taskAffinity的task中,如果相同taskAffinity的task是singleInstance的,那么会新建同名taskAffinity的task,然后放入.

准备条件:
    ActivityA: android:launchMode="standard"       android:taskAffinity="hello.world"
    ActivityB: android:launchMode="singleInstance" android:taskAffinity="hello.everyone"
    ActivityC: android:launchMode="singleTask"     android:taskAffinity="hello.everyone"

步骤:
    打开ActivityA -> startActivity到ActivityB -> startActivity到ActivityC
    
结果:
    Stack #17: type=standard mode=fullscreen
         Running activities (most recent first):
            TaskRecord{a26014f #353 A=hello.everyone U=0 StackId=17 sz=1}
                Run #0: ActivityRecord{358157e u0 com.example.hurshi.app_a/.AppA_ActivityC t353}

    Stack #16: type=standard mode=fullscreen
        Running activities (most recent first):
            TaskRecord{6c18ba #352 A=hello.everyone U=0 StackId=16 sz=1}
                Run #0: ActivityRecord{68f9e46 u0 com.example.hurshi.app_a/.AppA_ActivityB t352}

    Stack #15: type=standard mode=fullscreen
        Running activities (most recent first):
            TaskRecord{8aed0dc #351 A=hello.world U=0 StackId=15 sz=1}
                Run #0: ActivityRecord{a37e4a8 u0 com.example.hurshi.app_a/.AppA_ActivityA t351}

由上述可知,ActivityC的taskAffinity虽然和ActivityB一致,但是因为ActivityB是singleInstance,所以ActivityC添加不到ActivityB所在的task中,ActivityC只能新建一个taskAffinity也是hello.every的不同的task.

什么时候会将目标Activity放置到新task中?
1. 目标Activity的launchMode设置为singleInstance的时候.
2. 目标Activity的launchMode设置为singleTask,同时设置目标Activity的taskAffinity不同于启动它的Activity
3. 欢迎补充......
launchMode 和 Intent Flag
- singleTop = FLAG_ACTIVITY_SINGLE_TOP
- singleTask = FLAG_ACTIVITY_CLEAR_TOP + FLAG_ACTIVITY_SINGLE_TOP

android:noHistory

错误理解: ~~具有此属性标识的Activity当导航到其他Activity上时，Activity栈将不记录其自身.~~ --- ❌
正确理解: 当当前Activity标记为noHistory时,跳转到其他Activity时,当前Activity被标记为finishing,并不会马上调用onDestory方法,它会在合适的时候调用onDestory.✅
上面"合适的时候"有:当这个Activity再次回到前台时,用户点击"Home"键时......欢迎补充,欢迎打脸

所以: 标记noHistory的Activity很有可能会导致回收不及时而引起内存问题. 👈👈👈

准备条件:
    ActivityA: 
    ActivityB: android:noHistory="true"
    ActivityC:

步骤1:
    打开ActivityA -> startActivity到ActivityB -> startActivity到ActivityC
    
结果1:
    Stack #54: type=standard mode=fullscreen
         Running activities (most recent first):
            TaskRecord{26b634f #418 A=com.application U=0 StackId=54 sz=3}
                Run #2: ActivityRecord{444fa10 u0 com.example.hurshi.app_a/.AppA_ActivityC t418}
                //最后的 "f" 标记表示 "finishing"
                Run #1: ActivityRecord{5c65974 u0 com.example.hurshi.app_a/.AppA_ActivityB t418 f}
                Run #0: ActivityRecord{d4ac684 u0 com.example.hurshi.app_a/.AppA_ActivityA t418}
                                
步骤2:
    按 back 键

结果2:
    Stack #54: type=standard mode=fullscreen
        Running activities (most recent first):
            TaskRecord{26b634f #418 A=com.application U=0 StackId=54 sz=1}
                Run #0: ActivityRecord{d4ac684 u0 com.example.hurshi.app_a/.AppA_ActivityA t418}