Java 获取片段中的NullPointerException错误
以下代码引发NullPointerException错误。我不明白为什么。您能检查一下吗?Java 获取片段中的NullPointerException错误,java,android,android-fragments,Java,Android,Android Fragments,以下代码引发NullPointerException错误。我不明白为什么。您能检查一下吗?在这里输入代码 我在一个主要活动中得到了2个片段,如下所示 RSSFeedActivity在此处输入代码 MyListFragment(包含一个按钮) DetailFragment(包含textview) /*********************此处的活动代码******************/ package com.example.oksijen02.unit2.multipanelFragmen
在这里输入代码
我在一个主要活动中得到了2个片段,如下所示
在此处输入代码
package com.example.oksijen02.unit2.multipanelFragment;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import com.example.oksijen02.intent.R;
public class RSSFeedActivity extends Activity implements MyListFragment.OnItemSelectedListener{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.u2_fragment_activity_main);
}
@Override public void onRSSItemSelected(String link) { Log.d("butona tiklandi", "onRSSItemSelected: ");
DetailFragment fragment = (DetailFragment) getFragmentManager().findFragmentById(R.id.detailFragment);
fragment.setText(link);
}
}
/*******************MyListFragment************************/
package com.example.oksijen02.unit2.multipanelFragment;
import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import com.example.oksijen02.intent.R;
public class MyListFragment extends Fragment {
private OnItemSelectedListener listener;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.u2_fragment_rsslist_overview,container,false);
Button detailButton = (Button) view.findViewById(R.id.detailButton);
detailButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
updateDetail("fake");
}
});
return view;
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
Log.d("in on attach", "onAttach");
if(context instanceof OnItemSelectedListener){
Log.d("context is not of ", "onAttach:");
listener = (OnItemSelectedListener) context;
}else{
throw new ClassCastException(context.toString()+" must implement MyListFragment.OnItemSelectedListener");
}
}
public interface OnItemSelectedListener{
public void onRSSItemSelected(String link);
}
public void updateDetail(String fake) {
Log.d("tikladi update", "updateDetail");
String newTime = String.valueOf(System.currentTimeMillis());
Log.d("newtime"+newTime, "updateDetail");
Log.d("listener"+listener.toString(), "updateDetail");
listener.onRSSItemSelected(newTime);
}
}
package com.example.oksijen02.unit2.multipanelFragment;
import android.app.Fragment;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.example.oksijen02.intent.R;
public class DetailFragment extends Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.u2_fragment_rss_item_detail, container,false);
return view;
}
public void setText(String url) {
TextView textview = (TextView) getView().findViewById(R.id.detailsText);
textview.setText(url);
}
}
/***********************详细片段代码******************************/
package com.example.oksijen02.unit2.multipanelFragment;
import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import com.example.oksijen02.intent.R;
public class MyListFragment extends Fragment {
private OnItemSelectedListener listener;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.u2_fragment_rsslist_overview,container,false);
Button detailButton = (Button) view.findViewById(R.id.detailButton);
detailButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
updateDetail("fake");
}
});
return view;
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
Log.d("in on attach", "onAttach");
if(context instanceof OnItemSelectedListener){
Log.d("context is not of ", "onAttach:");
listener = (OnItemSelectedListener) context;
}else{
throw new ClassCastException(context.toString()+" must implement MyListFragment.OnItemSelectedListener");
}
}
public interface OnItemSelectedListener{
public void onRSSItemSelected(String link);
}
public void updateDetail(String fake) {
Log.d("tikladi update", "updateDetail");
String newTime = String.valueOf(System.currentTimeMillis());
Log.d("newtime"+newTime, "updateDetail");
Log.d("listener"+listener.toString(), "updateDetail");
listener.onRSSItemSelected(newTime);
}
}
package com.example.oksijen02.unit2.multipanelFragment;
import android.app.Fragment;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.example.oksijen02.intent.R;
public class DetailFragment extends Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.u2_fragment_rss_item_detail, container,false);
return view;
}
public void setText(String url) {
TextView textview = (TextView) getView().findViewById(R.id.detailsText);
textview.setText(url);
}
}
错误如下所示:
PID: 15763 java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference at com.example.oksijen02.unit2.multipanelFragment.MyListFragment.updateDetail(MyListFragment.java:59) at com.example.oksijen02.unit2.multipanelFragment.MyListFragment$1.onClick(MyListFragment.java:30) at android.view.View.performClick(View.java:5181) at android.view.View$PerformClick.run(View.java:20887) at
当我在网站上搜索时,我找到了为什么onAttach方法不调用的答案。请从中找到答案 因此,我在MyListFragment代码中添加了以下代码:
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
if(activity instanceof OnItemSelectedListener){
Log.d("context is not of ", "onAttach:");
listener = (OnItemSelectedListener) activity;
}else{
throw new ClassCastException(activity.toString()+" must implement MyListFragment.OnItemSelectedListener");
}
}