java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法"android.view.View android.app.Activity.findViewById(int)" [英] java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.app.Activity.findViewById(int)' on a null object reference
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问题描述
我的Android项目中总是出现错误.
I always get an Error in my Android Project.
java.lang.NullPointerException:尝试调用虚拟方法 'null上的'android.view.View android.app.Activity.findViewById(int)' 对象引用
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.app.Activity.findViewById(int)' on a null object reference
在我的MainActivity中,我正在调用FragmentStart类.
In my MainActivity i am calling the class FragmentStart.
FragmentStart.class
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
public class FragmentStart extends Fragment {
//Define Listview
private ListView startList;
private String[] stringList;
Activity activity = getActivity();
public FragmentStart() {
//
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_start, container, false);
// Create ListView start
startList = (ListView) rootView.findViewById(R.id.startList);
stringList = getResources().getStringArray(R.array.startList);
if (activity != null) {
ArrayAdapter<String> objAdapter = new ArrayAdapter<String>(activity, android.R.layout.simple_list_item_1, stringList);
startList.setAdapter(objAdapter);
startList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
switch (startList.getPositionForView(view)) {
case 0:
// ...
break;
}
}
});
}
// Create ListView end
//New Entry
Button add = (Button) activity.findViewById(R.id.add);
add.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(view.getContext(), addItem.class);
startActivityForResult(myIntent, 0);
}
});
return rootView;
}
}
推荐答案
除了@Selvin指出的内容外,它看起来像这样:
In addition to what @Selvin pointed out, it looks like this:
Button add = (Button) activity.findViewById(R.id.add);
...应更改为此:
Button add = (Button) rootView.findViewById(R.id.add);
这篇关于java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法"android.view.View android.app.Activity.findViewById(int)"的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
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