在android中对SQLite Db执行查询时出现NullPointerException [重复]

Question

现在我在这里得到空指针异常。在 ViewAllData 方法 myAdapter = new SQLCustomViewAllDataAdapter(SQLViewAllData.this,aList); here 中，我在创建构造函数时遇到错误。

SQLViewAllData.java

public class SQLViewAllData extends Activity {

private SQLDbHelper myDbHelper;
private SQLCustomViewAllDataAdapter myAdapter;
private ListView myListView;
private ArrayList<SQLPojo.UserDetails> aList = new ArrayList<>();
//private Context myContext;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.listview_view_data);
    //myContext = this;

    widgetInitialization();
    viewAllData();
}
//Initializing Widgets
public void widgetInitialization() {
    myDbHelper = new SQLDbHelper( this );
    myListView = (ListView)findViewById( R.id.listview_view_data_LV );
}

public ArrayList<SQLPojo.UserDetails> getUserInfo(){
    return myDbHelper.getUserDetails();
}

//view all data stored in DB
public void viewAllData() {
    aList = getUserInfo();
    myAdapter = new SQLCustomViewAllDataAdapter(SQLViewAllData.this,aList);
    myListView.setAdapter(myAdapter);
}

}

Answer 1

你需要改变：

myDbHelper = new SQLDbHelper( myContext );

到

myDbHelper = new SQLDbHelper(this);

同时删除“Activity myContext”字段，因为您的类已经扩展了 Activity。

Answer 2

你还没有初始化上下文，即 myContext