android安装新版本，双进程问题

现象：覆盖安装新版本apk，点击hone键，再点击又会重新启动，不会重新打开上次界面。

解决办法:

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;
}

stack overflow：
http://stackoverflow.com/questions/16283079/re-launch-of-activity-on-home-button-but-only-the-first-time/16447508#16447508