【Activity】Activity的启动模式：SingleTop

目录

1. 概述

2. 场景1：MainActivity->SecondActivity->SecondActivity

2.1 启动MainActivity

2.1.1 生命周期

2.1.2 Activity栈

2.2 MainActivity中启动SecondActivity

2.2.1 生命周期

2.2.2 Activity栈

2.3 SecondActivity中启动SecondActivity

2.3.1 生命周期

2.3.2 Activity栈

3.场景2：MainActivity->SecondActivity->MainActivity->SecondActivity

3.1 启动MainActivity

3.1.1 生命周期

3.1.2 Activity栈

3.2 MainActivity中启动SecondActivity

3.2.1 生命周期

3.2.2 Activity栈

3.3 SecondActivity中启动MainActivity

3.3.1 生命周期

3.3.2 Activity栈

3.4 MainActivity中启动SecondActivity

3.4.1 生命周期

3.4.2 Activity栈

4.总结

---

1. 概述

官方文档对“singleTop”启动模式的说明：

“如果目标任务在其堆栈顶部已有一个 Activity 实例，那么该实例将接收新 Intent（通过调用 onNewIntent()）；此时不会创建新实例。在其他情况下 — 例如，如果“singleTop”的一个现有实例虽在目标任务内，但未处于堆栈顶部，或者虽然位于堆栈顶部，但不在目标任务中 — 则系统会创建一个新实例并将其推送到堆栈上。”

接着就用Demo来验证一下。

Demo中的launchMode：

MainActivity-Standard
SecondActivity-SingleTop

2. 场景1：MainActivity->SecondActivity->SecondActivity

2.1 启动MainActivity

2.1.1 生命周期

2019-02-25 09:00:21.765 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onCreate:this=com.maureen.testtwoactivity.MainActivity@f6993c1
2019-02-25 09:00:21.897 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onStart:this=com.maureen.testtwoactivity.MainActivity@f6993c1
2019-02-25 09:00:21.900 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onResume:this=com.maureen.testtwoactivity.MainActivity@f6993c1

2.1.2 Activity栈

TaskRecord{4c3267a #37 A=com.maureen.testtwoactivity U=0 StackId=6 sz=1}
        Run #0: ActivityRecord{bb2ee2f u0 com.maureen.testtwoactivity/.MainActivity t37}

2.2 MainActivity中启动SecondActivity

2.2.1 生命周期

2019-02-25 09:00:59.625 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onPause:this=com.maureen.testtwoactivity.MainActivity@f6993c1
2019-02-25 09:00:59.690 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onCreate:this=com.maureen.testtwoactivity.SecondActivity@6c8c7b9
2019-02-25 09:00:59.821 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onStart:this=com.maureen.testtwoactivity.SecondActivity@6c8c7b9
2019-02-25 09:00:59.825 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onResume:this=com.maureen.testtwoactivity.SecondActivity@6c8c7b9
2019-02-25 09:01:00.570 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onStop:this=com.maureen.testtwoactivity.MainActivity@f6993c1
2019-02-25 09:01:00.573 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onSaveInstanceState:this=com.maureen.testtwoactivity.MainActivity@f6993c1

2.2.2 Activity栈

TaskRecord{4c3267a #37 A=com.maureen.testtwoactivity U=0 StackId=6 sz=2}
        Run #1: ActivityRecord{ed1f421 u0 com.maureen.testtwoactivity/.SecondActivity t37}
        Run #0: ActivityRecord{bb2ee2f u0 com.maureen.testtwoactivity/.MainActivity t37}

2.3 SecondActivity中启动SecondActivity

2.3.1 生命周期

2019-02-25 09:01:33.386 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onPause:this=com.maureen.testtwoactivity.SecondActivity@6c8c7b9
2019-02-25 09:01:33.387 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onNewIntent:this=com.maureen.testtwoactivity.SecondActivity@6c8c7b9
2019-02-25 09:01:33.390 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onResume:this=com.maureen.testtwoactivity.SecondActivity@6c8c7b9

2.3.2 Activity栈

TaskRecord{4c3267a #37 A=com.maureen.testtwoactivity U=0 StackId=6 sz=2}
        Run #1: ActivityRecord{ed1f421 u0 com.maureen.testtwoactivity/.SecondActivity t37}
        Run #0: ActivityRecord{bb2ee2f u0 com.maureen.testtwoactivity/.MainActivity t37}

3.场景2：MainActivity->SecondActivity->MainActivity->SecondActivity

3.1 启动MainActivity

3.1.1 生命周期

2019-02-25 09:05:37.417 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onCreate:this=com.maureen.testtwoactivity.MainActivity@a20eef8
2019-02-25 09:05:37.599 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onStart:this=com.maureen.testtwoactivity.MainActivity@a20eef8
2019-02-25 09:05:37.603 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onResume:this=com.maureen.testtwoactivity.MainActivity@a20eef8

3.1.2 Activity栈

TaskRecord{90f809a #38 A=com.maureen.testtwoactivity U=0 StackId=7 sz=1}
        Run #0: ActivityRecord{ebfb748 u0 com.maureen.testtwoactivity/.MainActivity t38}

3.2 MainActivity中启动SecondActivity

3.2.1 生命周期

2019-02-25 09:06:32.960 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onPause:this=com.maureen.testtwoactivity.MainActivity@a20eef8
2019-02-25 09:06:33.055 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onCreate:this=com.maureen.testtwoactivity.SecondActivity@a7068ff
2019-02-25 09:06:33.182 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onStart:this=com.maureen.testtwoactivity.SecondActivity@a7068ff
2019-02-25 09:06:33.185 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onResume:this=com.maureen.testtwoactivity.SecondActivity@a7068ff
2019-02-25 09:06:33.914 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onStop:this=com.maureen.testtwoactivity.MainActivity@a20eef8
2019-02-25 09:06:33.916 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onSaveInstanceState:this=com.maureen.testtwoactivity.MainActivity@a20eef

3.2.2 Activity栈

TaskRecord{90f809a #38 A=com.maureen.testtwoactivity U=0 StackId=7 sz=2}
        Run #1: ActivityRecord{c9d2cc1 u0 com.maureen.testtwoactivity/.SecondActivity t38}
        Run #0: ActivityRecord{ebfb748 u0 com.maureen.testtwoactivity/.MainActivity t38}

3.3 SecondActivity中启动MainActivity

3.3.1 生命周期

2019-02-25 09:07:16.659 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onPause:this=com.maureen.testtwoactivity.SecondActivity@a7068ff
2019-02-25 09:07:16.750 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onCreate:this=com.maureen.testtwoactivity.MainActivity@84a0e18
2019-02-25 09:07:16.861 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onStart:this=com.maureen.testtwoactivity.MainActivity@84a0e18
2019-02-25 09:07:16.864 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onResume:this=com.maureen.testtwoactivity.MainActivity@84a0e18
2019-02-25 09:07:17.591 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onStop:this=com.maureen.testtwoactivity.SecondActivity@a7068ff
2019-02-25 09:07:17.593 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onSaveInstanceState:this=com.maureen.testtwoactivity.SecondActivity@a7068ff

3.3.2 Activity栈

TaskRecord{90f809a #38 A=com.maureen.testtwoactivity U=0 StackId=7 sz=3}
        Run #2: ActivityRecord{1219cd8 u0 com.maureen.testtwoactivity/.MainActivity t38}
        Run #1: ActivityRecord{c9d2cc1 u0 com.maureen.testtwoactivity/.SecondActivity t38}
        Run #0: ActivityRecord{ebfb748 u0 com.maureen.testtwoactivity/.MainActivity t38}

3.4 MainActivity中启动SecondActivity

3.4.1 生命周期

2019-02-25 09:08:13.364 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onPause:this=com.maureen.testtwoactivity.MainActivity@84a0e18
2019-02-25 09:08:13.416 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onCreate:this=com.maureen.testtwoactivity.SecondActivity@e5b1142
2019-02-25 09:08:13.519 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onStart:this=com.maureen.testtwoactivity.SecondActivity@e5b1142
2019-02-25 09:08:13.522 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]SecondActivity: onResume:this=com.maureen.testtwoactivity.SecondActivity@e5b1142
2019-02-25 09:08:14.244 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onStop:this=com.maureen.testtwoactivity.MainActivity@84a0e18
2019-02-25 09:08:14.246 3508-3508/com.maureen.testtwoactivity D/[APP_Maureen]MainActivity: onSaveInstanceState:this=com.maureen.testtwoactivity.MainActivity@84a0e18

3.4.2 Activity栈

TaskRecord{90f809a #38 A=com.maureen.testtwoactivity U=0 StackId=7 sz=4}
        Run #3: ActivityRecord{14d1dab u0 com.maureen.testtwoactivity/.SecondActivity t38} //在栈顶，栈中包含两个SecondActivity实例
        Run #2: ActivityRecord{1219cd8 u0 com.maureen.testtwoactivity/.MainActivity t38}
        Run #1: ActivityRecord{c9d2cc1 u0 com.maureen.testtwoactivity/.SecondActivity t38}
        Run #0: ActivityRecord{ebfb748 u0 com.maureen.testtwoactivity/.MainActivity t38}

4.总结

就如同官方文档说明的，以“singleTop”模式启动的Activity：

• 如果目标任务中已经存在该Activity实例，且该实例位于栈顶，则调用该实例的onNewIntent()，而不是创建新的实例（见场景1）；
• 如果目标任务中已经存在该Activity实例，但是该实例不是位于栈顶，则创建新的实例（见场景2）；
• 如果已经有该Activity实例位于栈顶，但是该任务不是目标任务，也要创建一个实例且将其推至目标任务的栈顶（暂未找到合适的例子）