Android 在后台释放主活动
每次应用程序进入后台，RAM开始填充，应用程序开始释放变量（如果我没有错，这是Android的正常行为，它会释放变量实例） 当我从后台带回应用程序时，应用程序会崩溃，因为我失去了主活动 如果根本没有活动，有没有办法重新启动此活动？ 是一个模棱两可的问题，但我发现这个问题，但我不认为是最好的选择Android 在后台释放主活动,android,activity-lifecycle,application-lifecycle,Android,Activity Lifecycle,Application Lifecycle,每次应用程序进入后台，RAM开始填充，应用程序开始释放变量（如果我没有错，这是Android的正常行为，它会释放变量实例） 当我从后台带回应用程序时，应用程序会崩溃，因为我失去了主活动 如果根本没有活动，有没有办法重新启动此活动？ 是一个模棱两可的问题，但我发现这个问题，但我不认为是最好的选择 ActivityManager mngr = (ActivityManager) getSystemService( ACTIVITY_SERVICE ); List<ActivityManage
ActivityManager mngr = (ActivityManager) getSystemService( ACTIVITY_SERVICE );
List<ActivityManager.RunningTaskInfo> taskList = mngr.getRunningTasks(10);
if(taskList.get(0).numActivities == 1 &&
taskList.get(0).topActivity.getClassName().equals(this.getClass().getName())) {
Log.i(TAG, "This is last activity in the stack");
}
com.XXXX.mg E/Uncaught Exception detected in thread {}: Unable to start activity ComponentInfo{com.XXXX.mg/com.XXXX.view.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.XXXX.view.MainActivity.showShoppingCartIcon()' on a null object reference
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.XXXX.mg/com.XXXX.view.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.XXXX.view.MainActivity.showShoppingCartIcon()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2426)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.XXXX.view.MainActivity.showShoppingCartIcon()' on a null object reference
at com.XXXX.view.shoppingCart.ShoppingCartFragment.onDetach(ShoppingCartFragment.java:411)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1202)
at android.support.v4.app.FragmentManagerImpl.removeFragment(FragmentManager.java:1349)
at android.support.v4.app.BackStackRecord.popFromBackStack(BackStackRecord.java:915)
at android.support.v4.app.FragmentManagerImpl.popBackStackState(FragmentManager.java:1722)
at android.support.v4.app.FragmentManagerImpl$3.run(FragmentManager.java:593)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:339)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:602)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1260)
at android.app.Activity.performStart(Activity.java:6261)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2389)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
我不确定你的应用程序是否因为失去了MainActivity而崩溃，你应该使用@pablobu建议的onSaveInstanceState编写代码，期待这种行为，这是正确的方法 我们能看看日志吗？如果您正在丢失实例的状态，那么很好，您应该保存这些状态并恢复它们，是因为片段吗？你也可以保存这些，这是一个很好的阅读 请，你能给我们你的logcat输出，这可能有助于我们了解到底发生了什么 编辑 通过Logcat编辑，尝试查看片段生命周期，onAttach比onActivityCreated（）先执行，因此，如果您的活动已被销毁，那么onAttach方法将不会包含您的活动，您应该等待直到重新创建活动 此外，你有你的
super.onAttach(activity);
/**
This method was deprecated in API level 23.
Use onAttach(Context) instead.
*/
@Override
public void onAttach(Context context) {
super.onAttach(context);
MainActivity mainActivity;
if (context instanceof Activity) {
mainActivity = (MainActivity) context;
try {
mListener = (OnFragmentInteractionListener) mainActivity;
/**
Since you are getting a reference and accesing attributes you should be careful
with NullPointerException, check if not null first.
Or better yet refactor a little your code using an interface to handle this behaviour or use
the one you already created and just tell the activity what to do.
*/
/*if(mainActivity != null) {
ma.openMyList = false;
ma.openMyAddress = false;
ma.hideSearchButton();
}*/
} catch (ClassCastException e) {
throw new ClassCastException(mainActivity.getClass().getSimpleName() + " must implement OnFragmentInteractionListener");
}
}
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
//since your Listener is global use mListener behaviour that I suggested here.
if (mListener != null){
mListener.openListOfSomething(false);
mListener.hideSearch();
}
}
我不确定你的应用程序是否因为失去了MainActivity而崩溃，你应该使用@pablobu建议的onSaveInstanceState编写代码，期待这种行为，这是正确的方法 我们能看看日志吗？如果您正在丢失实例的状态，那么很好，您应该保存这些状态并恢复它们，是因为片段吗？你也可以保存这些，这是一个很好的阅读 请，你能给我们你的logcat输出，这可能有助于我们了解到底发生了什么 编辑 通过Logcat编辑，尝试查看片段生命周期，onAttach比onActivityCreated（）先执行，因此，如果您的活动已被销毁，那么onAttach方法将不会包含您的活动，您应该等待直到重新创建活动 此外，你有你的
super.onAttach(activity);
/**
This method was deprecated in API level 23.
Use onAttach(Context) instead.
*/
@Override
public void onAttach(Context context) {
super.onAttach(context);
MainActivity mainActivity;
if (context instanceof Activity) {
mainActivity = (MainActivity) context;
try {
mListener = (OnFragmentInteractionListener) mainActivity;
/**
Since you are getting a reference and accesing attributes you should be careful
with NullPointerException, check if not null first.
Or better yet refactor a little your code using an interface to handle this behaviour or use
the one you already created and just tell the activity what to do.
*/
/*if(mainActivity != null) {
ma.openMyList = false;
ma.openMyAddress = false;
ma.hideSearchButton();
}*/
} catch (ClassCastException e) {
throw new ClassCastException(mainActivity.getClass().getSimpleName() + " must implement OnFragmentInteractionListener");
}
}
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
//since your Listener is global use mListener behaviour that I suggested here.
if (mListener != null){
mListener.openListOfSomething(false);
mListener.hideSearch();
}
}
您可以使用捆绑包savedInstatceState，它在OnCreate和类似方法中给出：
private String aVariable;
@Override
public void onCreate (Bundle savedInstantceState) {
super.onCreate(savedInstanceState);
// Get the variable from savedInstanceState, if it isn't empty.
// If it is empty, it could be the first Activity run.
try {
aVariable = savedInstanceState.get("Key");
} catch (NullPointerException e) {
aVariable = "Baum";
}
}
@Override
public void onSaveInstanceState(Bundle outState){
super.onSaveInstanceState(outState);
outState.putString(aVariable, "Key");
}
稍后，当活动将被销毁时，将调用onSaveInstanceState。在这里，您可以将变量（aVariable）保存在一个键（“键”）下。您可以使用Bundle savedinStatEstate，它在OnCreate和类似方法中给出：
private String aVariable;
@Override
public void onCreate (Bundle savedInstantceState) {
super.onCreate(savedInstanceState);
// Get the variable from savedInstanceState, if it isn't empty.
// If it is empty, it could be the first Activity run.
try {
aVariable = savedInstanceState.get("Key");
} catch (NullPointerException e) {
aVariable = "Baum";
}
}
@Override
public void onSaveInstanceState(Bundle outState){
super.onSaveInstanceState(outState);
outState.putString(aVariable, "Key");
}
稍后，当活动将被销毁时，将调用onSaveInstanceState。在这里，您可以将变量（aVariable）保存在一个键（“键”）下。看起来您根本不需要检查是否没有活动，只需要在从内存中删除活动之前存储活动状态，然后恢复到该状态。在这里检查onSaveInstanceState和onRestoreInstanceState或onCreate，但我可以用完整的活动来完成吗@PABLOBUW什么是完整活动？我会更新我的问题。通过更新，检查onAttach首先执行的片段生命周期，而不是onActivityCreated（），因此尝试在onActivityCreated（）上执行此操作。看起来你根本不需要检查是否没有活动，只需要在将活动状态从内存中删除之前存储它，然后恢复到该状态。在这里检查onSaveInstanceState和onRestoreInstanceState或onCreate，但我可以用完整的活动来完成吗@PABLOBUW什么是完全活动？我会更新我的问题。好吧，通过更新，检查onAttach首先执行的片段生命周期，而不是onActivityCreated（），所以尝试在onActivityCreated（）上执行。哦，对不起，它可能会重复第一个答案中的内容。哦，对不起，它可能会重复第一个答案中的内容。