Android启动页重复启动问题-白红宇

问题描述 当时用 Android 系统installer 安装应用后，点击打开应用，按home键切后台点击icon启动，会导致root activity重复启动。导致应用异常、卡顿等。

原因

Welcome to the ever-growing list of users who have been bitten by this one. This is a well-known and long-standing Android bug. in the way applications get launched the first time from the installer, web-browser and via IDE (IntelliJ, Eclipse, etc.). See these issues filed long ago related to the problem: http://code.google.com/p/android/issues/detail?id=2373 http://code.google.com/p/android/issues/detail?id=26658 It is still broken and you cannot prevent this from happening. The only thing you can do is to detect when Android has launched a second instance of your root activity into an existing task. You can do this by putting this code in onCreate() of your root activity:

解决办法 在root activity的onCreate()中添加这句话即可解决。

if (!isTaskRoot()) {    // Android launched another instance of the root activity into an existing task    //  so just quietly finish and go away, dropping the user back into the activity    //  at the top of the stack (ie: the last state of this task)    finish();    return;}复制代码

/** * Return whether this activity is the root of a task.  The root is the * first activity in a task. * * @return True if this is the root activity, else false. */ // 返回当前activity是否为task的根activity,root意味着在是在task中的第一个activity.public boolean isTaskRoot() {    try {        return ActivityManagerNative.getDefault().getTaskForActivity(mToken, true) >= 0;    } catch (RemoteException e) {        return false;    }}复制代码

引用链接： https://stackoverflow.com/questions/16283079/re-launch-of-activity-on-home-button-but-only-the-first-time/16447508#16447508

相关链接： https://blog.csdn.net/cppalien/article/details/41958767 https://blog.csdn.net/u013039472/article/details/53284312 https://blog.csdn.net/singwhatiwanna/article/details/9294285

附录：下面是一些异常日志信息，

通过下面命令可以常看到当前应用的Activity堆栈情况

adb shell dumpsys activity activities | grep com.package.name复制代码

Activities=[ActivityRecord{232df185 u0 com.package.name/.ui.welcome.LaunchActivity t135}, ActivityRecord{328bcab9 u0 com.package.name/.ui.main.MainActivity t135}, ActivityRecord{3ef044dc u0 com.package.name/.ui.room.RoomActivity t135}, ActivityRecord{339781a4 u0 com.package.name/.ui.show.ShowActivity t135}, ActivityRecord{15a663ed u0 com.package.name/.ui.welcome.LaunchActivity t135}]      * Hist #4: ActivityRecord{15a663ed u0 com.package.name/.ui.welcome.LaunchActivity t135}          packageName=com.package.name processName=com.package.name          app=ProcessRecord{31ce96e8 16228:com.package.name/u0a148}          Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10600000 cmp=com.package.name/.ui.welcome.LaunchActivity (has extras) }          frontOfTask=false task=TaskRecord{2d6e9434 #135 A=com.package.name U=0 sz=5}          taskAffinity=com.package.name          realActivity=com.package.name/.ui.welcome.LaunchActivity          baseDir=/data/app/com.package.name-1/base.apk          dataDir=/data/data/com.package.name      * Hist #3: ActivityRecord{339781a4 u0 com.package.name/.ui.show.ShowActivity t135}          packageName=com.package.name processName=com.package.name          launchedFromUid=10148 launchedFromPackage=com.package.name userId=0          app=ProcessRecord{31ce96e8 16228:com.package.name/u0a148}          Intent { cmp=com.package.name/.ui.show.ShowActivity (has extras) }          frontOfTask=false task=TaskRecord{2d6e9434 #135 A=com.package.name U=0 sz=5}          taskAffinity=com.package.name          realActivity=com.package.name/.ui.show.ShowActivity          baseDir=/data/app/com.package.name-1/base.apk          dataDir=/data/data/com.package.name      * Hist #2: ActivityRecord{3ef044dc u0 com.package.name/.ui.room.RoomActivity t135}          packageName=com.package.name processName=com.package.name          launchedFromUid=10148 launchedFromPackage=com.package.name userId=0          app=ProcessRecord{31ce96e8 16228:com.package.name/u0a148}          Intent { cmp=com.package.name/.ui.room.RoomActivity (has extras) }          frontOfTask=false task=TaskRecord{2d6e9434 #135 A=com.package.name U=0 sz=5}          taskAffinity=com.package.name          realActivity=com.package.name/.ui.room.RoomActivity          baseDir=/data/app/com.package.name-1/base.apk          dataDir=/data/data/com.package.name      * Hist #1: ActivityRecord{328bcab9 u0 com.package.name/.ui.main.MainActivity t135}          packageName=com.package.name processName=com.package.name          launchedFromUid=10148 launchedFromPackage=com.package.name userId=0          app=ProcessRecord{31ce96e8 16228:com.package.name/u0a148}          Intent { flg=0x4000000 cmp=com.package.name/.ui.main.MainActivity }          frontOfTask=false task=TaskRecord{2d6e9434 #135 A=com.package.name U=0 sz=5}          taskAffinity=com.package.name          realActivity=com.package.name/.ui.main.MainActivity          baseDir=/data/app/com.package.name-1/base.apk          dataDir=/data/data/com.package.name      * Hist #0: ActivityRecord{232df185 u0 com.package.name/.ui.welcome.LaunchActivity t135}          packageName=com.package.name processName=com.package.name          app=ProcessRecord{31ce96e8 16228:com.package.name/u0a148}          Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 pkg=com.package.name cmp=com.package.name/.ui.welcome.LaunchActivity }          frontOfTask=true task=TaskRecord{2d6e9434 #135 A=com.package.name U=0 sz=5}          taskAffinity=com.package.name          realActivity=com.package.name/.ui.welcome.LaunchActivity          baseDir=/data/app/com.package.name-1/base.apk          dataDir=/data/data/com.package.name      TaskRecord{2d6e9434 #135 A=com.package.name U=0 sz=5}        Run #9: ActivityRecord{15a663ed u0 com.package.name/.ui.welcome.LaunchActivity t135}      TaskRecord{2d6e9434 #135 A=com.package.name U=0 sz=5}        Run #7: ActivityRecord{339781a4 u0 com.package.name/.ui.show.ShowActivity t135}        Run #6: ActivityRecord{3ef044dc u0 com.package.name/.ui.room.RoomActivity t135}        Run #5: ActivityRecord{328bcab9 u0 com.package.name/.ui.main.MainActivity t135}        Run #4: ActivityRecord{232df185 u0 com.package.name/.ui.welcome.LaunchActivity t135}    mResumedActivity: ActivityRecord{15a663ed u0 com.package.name/.ui.welcome.LaunchActivity t135}  mFocusedActivity: ActivityRecord{15a663ed u0 com.package.name/.ui.welcome.LaunchActivity t135}复制代码

可以看到LaunchActivity activity存在两个，这里的LaunchActivity就是root activity，是不应该存在多个的。第一次启动的intent

Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 pkg=com.package.name cmp=com.package.name/.ui.welcome.LaunchActivity }复制代码

flag为FLAG_ACTIVITY_NEW_TASK 0x10000000。

/** * If set, this activity will become the start of a new task on this * history stack.  A task (from the activity that started it to the * next task activity) defines an atomic group of activities that the * user can move to.  Tasks can be moved to the foreground and background; * all of the activities inside of a particular task always remain in * the same order.  See * Tasks and Back * Stack for more information about tasks. * * This flag is generally used by activities that want * to present a "launcher" style behavior: they give the user a list of * separate things that can be done, which otherwise run completely * independently of the activity launching them. * * 
When using this flag, if a task is already running for the activity * you are now starting, then a new activity will not be started; instead, * the current task will simply be brought to the front of the screen with * the state it was last in.  See {@link #FLAG_ACTIVITY_MULTIPLE_TASK} for a flag * to disable this behavior. * * 
This flag can not be used when the caller is requesting a result from * the activity being launched. */// 如果设置了，将会在历史堆栈中新启动一个task,activity为这个task的第一个元素。task(从当前activity// 开始到下个task监理)定义了一个Activity元子组，用户可以进行移动。tasks可以从前后台进行切换。// 在指定的task中的所有activity, 始终保持相同的顺序。// 这个flag通常使用在，activity想要以launcher的形式出现；他们会给用户一个单独的列表，否则完全独立运行与// 启动他们的activity。// 当使用这个flag时，如果一个task已经运行了你正在启动的activity，那么一个新的activity不会开始;代替的是// 当前的task只需要带着最后的状态运行到前台。// 当调用者想要从当前启动的activity获得结果，是不能使用这个flag的。public static final int FLAG_ACTIVITY_NEW_TASK = 0x10000000;复制代码

而在第二次启动的LaunchActivity时intent为：

Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10600000 cmp=com.package.name/.ui.welcome.LaunchActivity (has extras) }复制代码

falg=FLAG_ACTIVITY_BROUGHT_TO_FRONT&FLAG_ACTIVITY_RESET_TASK_IF_NEEDED&FLAG_ACTIVITY_NEW_TASK

/** * This flag is not normally set by application code, but set for you by * the system as described in the * {@link android.R.styleable#AndroidManifestActivity_launchMode * launchMode} documentation for the singleTask mode. *//** * 这个flag通常不需要由应用程序代码设置，但是系统会在singleTask模式中设置。 */public static final int FLAG_ACTIVITY_BROUGHT_TO_FRONT = 0x00400000;/** * If set, and this activity is either being started in a new task or * bringing to the top an existing task, then it will be launched as * the front door of the task.  This will result in the application of * any affinities needed to have that task in the proper state (either * moving activities to or from it), or simply resetting that task to * its initial state if needed. */public static final int FLAG_ACTIVITY_RESET_TASK_IF_NEEDED = 0x00200000;复制代码