我发现异常是因为在onResume（）中调用了super.onResume（），异常细节是：
07-08 10:10:00.483 26883-26883/E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.xxx.xxx, PID: 26883
java.lang.RuntimeException: Unable to resume activity {com.xxx.xxx/com.xxx.xxx.MainActivity}: java.lang.NullPointerException: Attempt to write to field 'int android.support.v4.app.Fragment.mNextAnim' on a null object reference
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2986)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3017)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to write to field 'int android.support.v4.app.Fragment.mNextAnim' on a null object reference
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:714)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1501)
at android.support.v4.app.FragmentActivity.onResume(FragmentActivity.java:426)
at com.xxx.xxx.MainActivity.onResume(MainActivity.java:74)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1257)
at android.app.Activity.performResume(Activity.java:6076)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2975)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3017)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
我认为原因是内存被回收，但我该如何解决呢？
我认为这是“MainActivity”的主要代码，它管理底部的四个片段
public RadioButton rbTabLottery, rbTabAward, rbTabCircle, rbTabMine;
private int selectedId = R.id.rb_tab_lottery;
private Fragment currentFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
EventBus.getDefault().register(this);
if (savedInstanceState == null) {
Fragment fragment = getFragment(selectedId);
getSupportFragmentManager().beginTransaction().add(R.id.fragment_container,fragment).commit();
currentFragment = fragment;
}
}
@Override
protected void initView() {//parent class is called
rbTabLottery = findView(R.id.rb_tab_lottery);
rbTabAward = findView(R.id.rb_tab_award);
rbTabCircle = findView(R.id.rb_tab_circle);
rbTabMine = findView(R.id.rb_tab_mine);
rbTabLottery.setOnCheckedChangeListener(this);
rbTabAward.setOnCheckedChangeListener(this);
rbTabCircle.setOnCheckedChangeListener(this);
rbTabMine.setOnCheckedChangeListener(this);
}
@Override
protected void onResume() {
super.onResume(); //the exception is here
if (selectedId == R.id.rb_tab_award){
rbTabAward.setChecked(true);
}else if (selectedId == R.id.rb_tab_circle){
rbTabCircle.setChecked(true);
}else if (selectedId == R.id.rb_tab_mine){
rbTabMine.setChecked(true);
}else {
selectedId = R.id.rb_tab_lottery;
rbTabLottery.setChecked(true);
}
Fragment fragment = getFragment(selectedId);
if (fragment != null){
addOrShowFragment(getSupportFragmentManager().beginTransaction(), fragment);
}
}
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
if (isChecked){
selectedId = buttonView.getId();
Fragment fragment = getFragment(selectedId);
if (fragment != null){
addOrShowFragment(getSupportFragmentManager().beginTransaction(),fragment);
}
}
}
private Fragment getFragment(int selectedId){
switch (selectedId) {
case R.id.rb_tab_lottery:
return TabLotteryFragment.getInstance();
case R.id.rb_tab_award:
return TabAwardFragment.getInstance();
case R.id.rb_tab_circle:
return TabCircleFragment.getInstance();
case R.id.rb_tab_mine:
return TabMineFragment.getInstance();
default:
return TabLotteryFragment.getInstance();
}
}
/**
* @param transaction
* @param fragment
*/
private void addOrShowFragment(FragmentTransaction transaction,
Fragment fragment) {
if (currentFragment == fragment)
return;
if (!fragment.isAdded()) {
transaction.hide(currentFragment).add(R.id.fragment_container, fragment,
String.valueOf(selectedId)).commitAllowingStateLoss();
} else {
transaction.hide(currentFragment).show(fragment).commitAllowingStateLoss();
}
currentFragment = fragment;
}
答案 0 :(得分：0)
确保您的应用在恢复时处于有效状态。
有一些重要的方法，例如：
protected void onSaveInstanceState(Bundle outState){}
public void onRestoreInstanceState(Bundle savedInstanceState){}
protected void onResume() {}
请参阅此文档Activity Lifecycle和onResume()