编辑：我已经解决了关于空指针异常的问题。这个问题完全不同。在这里，我不知道为什么slot3被称为空指针，即使我在oncrrateview中声明它。另一点需要注意的是，当我尝试从oncrrateview本身访问变量时，没有错误。只有当我进行片段通信时才会出现错误。那个问题对我的问题没有任何答案。所以请删除重复的标记。
这是我的代码。这是我在stackoverflow中的第一个问题。请忍受我的询问方式。
public class HeaderScrollFragment extends Fragmen {
OnModeSelectedListener modeCallBack;
public View myFragmentView;
Button slot1,slot2,slot3,slot4,slot5;
int selectedMode;
public interface OnModeSelectedListener{
public void OnModeChangedCallBack(int x);
public void inputDataCallback(int y);
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
modeCallBack = (HeaderScrollFragment.OnModeSelectedListener) context;
} catch (ClassCastException e) {
throw new ClassCastException(context.toString()
+ " must implement OnHeadlineSelectedListener");
}
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
myFragmentView = inflater.inflate(R.layout.activity_header_scroll,container,false);
manyScreens();
slot1 = (Button) myFragmentView.findViewById(R.id.header_slot1);
slot2 = (Button) myFragmentView.findViewById(R.id.header_slot2);
slot3 = (Button) myFragmentView.findViewById(R.id.header_slot3);
slot4 = (Button) myFragmentView.findViewById(R.id.header_slot4);
slot5 = (Button) myFragmentView.findViewById(R.id.header_slot5);
slot1.setOnClickListener(this);
slot2.setOnClickListener(this);
slot3.setOnClickListener(this);
slot4.setOnClickListener(this);
slot5.setOnClickListener(this);
selectedMode = 3;
return myFragmentView;
}
private void manyScreens() {
}
public void onTopicChanged(int x){
switch (x){
case 1:
slot3.setText(R.string.next_m);
slot5.setText(R.string.mg);
break;
case 2:
slot3.setText(R.string.next_e);
slot5.setText(R.string.tg);
break;
case 3:
slot3.setText(R.string.next_v);
slot5.setText(R.string.y_g);
break;
}
onModeChanged(3);
}
public void onModeChanged(int x){
slot1.setSelected(false);
slot2.setSelected(false);
slot3.setSelected(false);
slot4.setSelected(false);
slot5.setSelected(false);
switch (x){
case 1:
slot1.setSelected(true);
break;
case 2:
slot2.setSelected(true);
break;
case 3:
slot3.setSelected(true);
break;
case 4:
slot4.setSelected(true);
break;
case 5:
slot5.setSelected(true);
break;
}
modeCallBack.OnModeChangedCallBack(x);
}
}
我的代码中有另一个片段是BottomMenuFragment。当我尝试从Bottom菜单片段与此片段进行通信时，它显示空指针异常。不要查看日志中的行号。基本上它显示了这条线 slot3.setText（R.string.next_episode）; 带有空指针异常
FATAL EXCEPTION: main
Process: com.batmansves.www.nextepisode, PID: 18087
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.batmansves.www.nextepisode/com.batmansves.www.nextepisode.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setText(java.lang.CharSequence)' 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 android.widget.Button.setText(java.lang.CharSequence)' on a null object reference
at com.batmansves.www.nextepisode.HeaderScrollFragment.onTopicChanged(HeaderScrollFragment.java:138)
at com.batmansves.www.nextepisode.MainActivity.TopicChangeCallback(MainActivity.java:69)
at com.batmansves.www.nextepisode.BottomMenuFragment.onTopicChanged(BottomMenuFragment.java:99)
at com.batmansves.www.nextepisode.BottomMenuFragment.onCreateView(BottomMenuFragment.java:74)
at android.app.Fragment.performCreateView(Fragment.java:2220)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:973)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1148)
at android.app.BackStackRecord.run(BackStackRecord.java:793)
at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1537)
at android.app.FragmentController.execPendingActions(FragmentController.java:325)
at android.app.Activity.performStart(Activity.java:6275)
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)
我认为正在发生的是将slot3作为空指针。但是我已经在onCreateView（）中定义了slot3。所以我实际上并不了解问题所在？