为什么我总是在Android Studio中遇到java.lang.nullpointerexception?
所以我试图将一个片段中的文本传递给主活动,并让主活动将其传递给另一个片段,以便可以显示它 以下是将片段发送到主活动的代码:为什么我总是在Android Studio中遇到java.lang.nullpointerexception?,java,android,android-fragments,nullpointerexception,Java,Android,Android Fragments,Nullpointerexception,所以我试图将一个片段中的文本传递给主活动,并让主活动将其传递给另一个片段,以便可以显示它 以下是将片段发送到主活动的代码: public class TopFragment extends Fragment{ private static EditText topInput; private static EditText bottomInput; FragmentInterface communicate; public interface FragmentInterfac
public class TopFragment extends Fragment{
private static EditText topInput;
private static EditText bottomInput;
FragmentInterface communicate;
public interface FragmentInterface{
public void sendTheInput(String topText,String bottomText);
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.top_fragment,container,false);
topInput = (EditText) view.findViewById(R.id.topInput);
bottomInput = (EditText) view.findViewById(R.id.bottomInput);
final Button submitButton = (Button)view.findViewById(R.id.submitButton);
submitButton.setOnClickListener(
new View.OnClickListener(){
public void onClick(View v){
buttonClicked(v);
}
}
);
return view;
}
public void buttonClicked(View view){
communicate.sendTheInput(topInput.getText().toString(),bottomInput.getText().toString());
}
}
以下是主要活动中的代码位:
@Override
public void sendTheInput(String topText, String bottomText) {
BottomFragment bottomFrag = (BottomFragment)getSupportFragmentManager().findFragmentById(R.id.bottomFragment);
bottomFrag.setBoxText(topText,bottomText);
}
下面是显示文本的片段代码:
public class BottomFragment extends Fragment{
private static EditText topTextBox;
private static EditText bottomTextBox;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.bottom_fragment,container,false);
return view;
}
public void setBoxText(String topText, String bottomText){
topTextBox.setText(topText);
bottomTextBox.setText(bottomText);
}
}
当我运行应用程序时,我没有运行时错误,但当我在我的emulator中单击按钮时,我得到以下信息:
08-07 13:20:48.125 4011-4011/com.example.vanessaanthony.fragmentreview E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.vanessaanthony.fragmentreview, PID: 4011
java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.vanessaanthony.fragmentreview.TopFragment$FragmentInterface.sendTheInput(java.lang.String, java.lang.String)' on a null object reference
at com.example.vanessaanthony.fragmentreview.TopFragment.buttonClicked(TopFragment.java:44)
at com.example.vanessaanthony.fragmentreview.TopFragment$1.onClick(TopFragment.java:35)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
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)
为什么我会收到此错误消息?您刚刚忘记在片段中设置
通信。我建议您在onAttach
public class TopFragment extends Fragment
{
private static EditText topInput;
private static EditText bottomInput;
FragmentInterface communicate;
public interface FragmentInterface{
public void sendTheInput(String topText,String bottomText);
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.top_fragment,container,false);
topInput = (EditText) view.findViewById(R.id.topInput);
bottomInput = (EditText) view.findViewById(R.id.bottomInput);
final Button submitButton = (Button)view.findViewById(R.id.submitButton);
submitButton.setOnClickListener(
new View.OnClickListener(){
public void onClick(View v){
buttonClicked(v);
}
}
);
return view;
}
public void onAttach(Activity activity)
{
super.onAttach(activity);
communicate = (FragmentInterface) activity;
}
public void buttonClicked(View view){
communicate.sendTheInput(topInput.getText().toString(),bottomInput.getText().toString());
}
}
确保您的活动实现了FragmentInterface
TopFragment.java中的第44行是什么?您的通信
对象是null
。检查您是否在主活动中实现了fragmentinterface?stacktrace明确指出,通信
为空。什么是通信
?@Codebender放置此片段的活动应该实现fragmentinterface,这将允许cast@Codebender很高兴听到这个消息