在android里，有4种activity的启动模式，分别为：
“standard” (默认)
“singletop”
“singletask”
“singleinstance”
在android应用中, activity是最核心的组件, 如何生成一个activity实例, 可以选择不同的启动模式, 即launchmode. 启动模式主要包括: standard, singletop, singletask, singleinstance.
标准模式在每次启动时, 都会创建实例; 三种单例模式, 会根据情况选择创建还是复用实例. 在activity启动中, 创建实例的生命周期: oncreate -> onstart -> onresume; 重用实例的生命周期: onnewintent -> onresume.
在androidmanifest的activity中, 使用launchmode属性, 可以设置启动模式, 默认是standard模式; 使用taskaffinity属性, 并添加包名, 可以设置activity栈, 默认是当前包名, 只能应用于single模式.
希望通过本文, 可以更好的理解activity的启动模式(launchmode).
全面解析activity启动模式(launchmode)
观察activity栈的脚本, 参考第5点 .
adb shell dumpsys activity | sed -n -e '/stack #/p' -e '/running activities/,/run #0/p'
1. standard
标准模式, 启动activity的默认模式, 被启动的activity 会运行于 启动的activity 栈, 因此必须使用activity的context启动, 不能使用application, 否则会报错.
如mainactivity启动testaactivity.
stack #1:
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running activities (most recent first):taskrecord{3caa65e3 #2711 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=2}run #1: activityrecord{36b06e99 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testaactivity t2711}run #0: activityrecord{27396226 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.mainactivity t2711}stack #0:running activities (most recent first):taskrecord{27d796c9 #2695 a=com.miui.home u=0 sz=1}run #0: activityrecord{2e5712cb u0 com.miui.home/.launcher.launcher t2695} |
栈内由下到上: mainactivity -> testaactivity.
2. singletop
栈顶复用模式. 只有activity位于栈顶, 重复启动时, 会使用默认实例, 即单例模式; 如果位于栈内, 则仍然会创建实例.
mainactivity启动testa, testa启动testb, testb启动自身, testb是单例. 观察栈内情况, testb只有一份实例, 第二次创建复用.
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running activities (most recent first):taskrecord{12abf566 #2712 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=3}run #2: activityrecord{187d7ff7 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2712}run #1: activityrecord{a551034 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testaactivity t2712}run #0: activityrecord{22f9cce4 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.mainactivity t2712} |
栈内: mainactivity -> testaactivity -> testbactivity
mainactivity启动testa, testa启动testb, testb启动testc, testc启动testb, testb是单例. 观察栈内情况, 由于testc是栈顶, testc启动testb, testb不是栈顶, 重新创建testb实例, 则保留两份testb.
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running activities (most recent first):taskrecord{1792f5f0 #2715 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=5}run #4: activityrecord{1e70110b u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2715}run #3: activityrecord{c7f4dce u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testcactivity t2715}run #2: activityrecord{254536cd u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2715}run #1: activityrecord{36b2da15 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testaactivity t2715}run #0: activityrecord{3a1c4a6a u0 me.chunyu.spike.wcl_activity_launchmode_demo/.mainactivity t2715} |
栈内: mainactivity -> testaactivity -> testbactivity ->testcactivity -> testbactivity
3. singletask
栈内复用模式, 只要activity在一个栈中存在, 多次调用时, 都不会创建实例, 即单例模式.
情况包含以下几种:
(1) 任务栈不存在, 初次启动singletask实例, 会创建任务栈和实例.
mainactivity启动testa, testa启动testb, testb是singletask, 并且任务栈不同. 观察可知, 系统包含两个任务栈, testb位于其他任务栈中.
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running activities (most recent first):taskrecord{d5d53d4 #2727 a=me.chunyu.spike.stack u=0 sz=1}run #2: activityrecord{1d720e55 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2727}taskrecord{a3f797d #2726 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=2}run #1: activityrecord{ffd689d u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testaactivity t2726}run #0: activityrecord{192310ac u0 me.chunyu.spike.wcl_activity_launchmode_demo/.mainactivity t2726} |
使用taskaffinity属性, 添加新的activity栈, 与singletask配合使用, standard模式无效.
新任务栈是 me.chunyu.spike.stack .
(2) 任务栈存在, 初次启动singletask实例, 会直接入栈, 与standard模式相同.
(3) 任务栈相同, 再次启动singletask实例, 实例会置于栈顶, 并清除其上面实例, 具有cleartop的效果.
mainactivity启动testa, testa启动testb, testb是singletask, testb启动testc, testc重新启动testb, 则testc会出栈. 观察可知, testc出栈, testb位于栈顶.
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running activities (most recent first):taskrecord{18230815 #2737 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=3}run #4: activityrecord{1126c300 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2737}run #3: activityrecord{3114fee8 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testaactivity t2737}run #2: activityrecord{f8e235d u0 me.chunyu.spike.wcl_activity_launchmode_demo/.mainactivity t2737} |
testc启动testb, singletask模式, 导致cleartop, testc出栈.
(4) 任务栈不同, 再次启动singletask实例, 会导致任务栈切换, 后台置于前台.
这比较难理解.mainactivity启动testa, testa启动testb(singletask实例, 不同任务栈), testb启动testc(与b类似), 则mainactivity和testa相同栈, testb和testc相同栈, 此时栈顶是testc. 按home键, 再次启动应用, 则默认任务栈会启动, testa启动, testa启动testc. 应用当前状态如下.
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running activities (most recent first):taskrecord{1d05e6c9 #2754 a=me.chunyu.spike.stack u=0 sz=2}run #4: activityrecord{3f77e822 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testcactivity t2754}taskrecord{3fe736d0 #2753 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=2}run #3: activityrecord{15f0470e u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testaactivity t2753}taskrecord{1d05e6c9 #2754 a=me.chunyu.spike.stack u=0 sz=2}run #2: activityrecord{181229e6 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2754}taskrecord{3fe736d0 #2753 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=2}run #1: activityrecord{28628d61 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.mainactivity t2753}taskrecord{2d646058 #2719 a=com.android.incallui u=0 sz=1} |
testc至于栈顶, 点击back键, 不是返回testa(启动testc的实例), 而是testb, 即优先返回相同栈的实例. 再次是testa, 然后是mainactivity, 依次出栈.
4. singleinstance
单实例模式, 启动时, 系统会为其创造一个单独的任务栈, 以后每次使用, 都会使用这个单例, 直到其被销毁, 属于真正的单例模式.
示例: mainactivity启动testa, testa启动testb(singleinstance模式),
testb启动testc, testc再启动testb, 则仍启动上一次的testb,
testc合并入默认栈(mainactivity+testa).
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running activities (most recent first):taskrecord{384e3928 #2765 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=1}run #3: activityrecord{1ffc5b6b u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2765}taskrecord{2ad03544 #2764 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=3}run #2: activityrecord{293d8c37 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testcactivity t2764}run #1: activityrecord{158bc0f3 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testaactivity t2764}run #0: activityrecord{77691cf u0 me.chunyu.spike.wcl_activity_launchmode_demo/.mainactivity t2764} |
5. startactivityforresult
thx@回调的幸福时光
startactivityforresult不同于startactivity, 使用launchmode模式启动activity时, 也会有一些不同, 可以正常传递数据, 但是无法连续创建自己时, 会生成多份实例.
testb(singletask模式)使用startactivity创建自己时, 会使用默认实例, 即单例; 而使用startactivityforresult创建自己时, 会生成一份新的示例.
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running activities (most recent first):taskrecord{323200ac #2786 a=me.chunyu.clwang.stack u=0 sz=3}run #4: activityrecord{3f9e14f3 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2786}run #3: activityrecord{30d8f17b u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2786}run #2: activityrecord{11b95b5c u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testbactivity t2786}taskrecord{c86e175 #2785 a=me.chunyu.spike.wcl_activity_launchmode_demo u=0 sz=2}run #1: activityrecord{3558d7c4 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.testaactivity t2785}run #0: activityrecord{1b8620c u0 me.chunyu.spike.wcl_activity_launchmode_demo/.mainactivity t2785} |
由此可知, 因为startactivityforresult需要返回值, 会保留实例, 覆盖单例效果.
注意: 4.x版本通过startactivityforresult启动singletask, 无法正常获取返回值, 参考 .
5.x以上版本修复此问题, 考虑兼容性, 不推荐使用startactivityforresult和singletask.
启动模式做为activity的重要属性, 还是需要比较透彻的掌握.
