我试图在保存项目后将项目添加到我的 ArrayAdapter，但它抛出 NullPointerException。谁能告诉我这是什么原因造成的？看起来信息已保存到数据库中，并且在重新加载应用程序时就在那里。
这是我的 java 文件，有问题的行是
adapter.addAll(character);
这是完整的文件
package com.fasttracksites.dnd5e;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Adapter;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import com.getbase.floatingactionbutton.FloatingActionButton;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private CustomCursorAdapter customAdapter;
private List<Character> characters;
private static final int ENTER_DATA_REQUEST_CODE = 1;
private ListView listView;
private Context ctx;
private ArrayAdapter<Character> adapter;
private static final String TAG = MainActivity.class.getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setTitle("Choose a Character");
ctx = getApplicationContext();
listView = (ListView) findViewById(R.id.characters);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Log.d(TAG, "clicked on item: " + position);
}
});
// Construct the data source
ArrayList<Character> arrayOfCharacters = new ArrayList<Character>();
// Create the adapter to convert the array to views
CharacterListAdapter adapter = new CharacterListAdapter(this, arrayOfCharacters);
// Attach the adapter to a ListView
listView.setAdapter(adapter);
characters = Character.listAll(Character.class);
adapter.addAll(characters);
final FloatingActionButton actionA = (FloatingActionButton) findViewById(R.id.addCharacter);
actionA.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
actionA.setTitle("Add Character clicked");
startActivityForResult(new Intent(MainActivity.this, AddCharacterActivity.class), ENTER_DATA_REQUEST_CODE);
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == ENTER_DATA_REQUEST_CODE && resultCode == RESULT_OK) {
Character character = new Character(data.getExtras().getString("tag_character_name"), data.getExtras().getString("tag_character_class"), data.getExtras().getInt("tag_character_level"));
character.save();
adapter.addAll(character); // This is causing the null pointer exception
}
}
}
class CharacterListAdapter extends ArrayAdapter<Character> {
// View lookup cache
private static class ViewHolder {
TextView name;
TextView classAndLevel;
}
public CharacterListAdapter(Context context, ArrayList<Character> characters) {
super(context, R.layout.list_characters, characters);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// Get the data item for this position
Character character = getItem(position);
// Check if an existing view is being reused, otherwise inflate the view
ViewHolder viewHolder; // view lookup cache stored in tag
if (convertView == null) {
viewHolder = new ViewHolder();
LayoutInflater inflater = LayoutInflater.from(getContext());
convertView = inflater.inflate(R.layout.list_characters, parent, false);
viewHolder.name = (TextView) convertView.findViewById(R.id.tvCharacterName);
viewHolder.classAndLevel = (TextView) convertView.findViewById(R.id.tvCharacterClassAndLevel);
convertView.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
// Populate the data into the template view using the data object
viewHolder.name.setText(character.name);
viewHolder.classAndLevel.setText(character.chosenClass + " - Level " + character.level);
// Return the completed view to render on screen
return convertView;
}
}
这是控制台的错误:
05-03 21:09:35.628 2106-2106/com.fasttracksites.dnd5e E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=Intent { cmp=com.fasttracksites.dnd5e/.AddCharacterActivity (has extras) }} to activity {com.fasttracksites.dnd5e/com.fasttracksites.dnd5e.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.deliverResults(ActivityThread.java:3367)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:3410)
at android.app.ActivityThread.access$1100(ActivityThread.java:141)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1304)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.fasttracksites.dnd5e.MainActivity.onActivityResult(MainActivity.java:78)
at android.app.Activity.dispatchActivityResult(Activity.java:5322)
at android.app.ActivityThread.deliverResults(ActivityThread.java:3363)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:3410)
at android.app.ActivityThread.access$1100(ActivityThread.java:141)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1304)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
发送 Intent 的代码是:
package com.fasttracksites.dnd5e;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;
public class AddCharacterActivity extends AppCompatActivity {
EditText editTextCharacterName;
EditText editTextCharacterClass;
EditText editTextCharacterLevel;
/**
* Called when the activity is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_character);
setTitle("Enter Your Character Info");
editTextCharacterName = (EditText) findViewById(R.id.et_character_name);
editTextCharacterClass = (EditText) findViewById(R.id.et_character_class);
editTextCharacterLevel = (EditText) findViewById(R.id.et_character_level);
}
public void onClickAdd (View btnAdd) {
String characterName = editTextCharacterName.getText().toString();
String characterClass = editTextCharacterClass.getText().toString();
Integer characterLevel = Integer.parseInt(editTextCharacterLevel.getText().toString());
if ( characterName.length() != 0 && characterClass.length() != 0 ) {
Intent newIntent = getIntent();
newIntent.putExtra("tag_character_name", characterName);
newIntent.putExtra("tag_character_class", characterClass);
newIntent.putExtra("tag_character_level", characterLevel);
this.setResult(RESULT_OK, newIntent);
finish();
}
}
}
最佳答案
改变:
CharacterListAdapter adapter =
new CharacterListAdapter(this, arrayOfCharacters);
到
adapter = new CharacterListAdapter(this, arrayOfCharacters);
出现问题是因为调用adapter.addAll 方法时onActivityResult 方法中的adapter 为null
关于java - ArrayAdapter 导致 java.lang.NullPointerException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30021280/