在android中使用简单列表项2时的NPE

Question

我试图将数据库中创建的两列的值设置为使用简单光标适配器的简单列表项2的两个文本视图，但我正在获得NPE。请帮助。
关于

我的代码是:

class NotesList extends ListActivity{
    private DataSource datasource;
     ArrayAdapter<Message> adapter;
     Cursor cursors = null;
     private SQLiteDatabase database;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list);
        datasource = new DataSource(this);
        datasource.open();

       // List<Message> values = datasource.getAllMessages();
    //    adapter = new ArrayAdapter<Message>(this, android.R.layout.simple_list_item_1, values);
    //     setListAdapter(adapter);

        String queryz = "SELECT " + MySQLiteHelper.COLUMN_ID + "," + MySQLiteHelper.COLUMN_MESSAGE+ " FROM " + MySQLiteHelper.TABLE_NAME ;
        cursors = database.rawQuery(queryz, null);
           ListAdapter adapter = new SimpleCursorAdapter(
                     this,
                     android.R.layout.simple_list_item_2,
                     cursors,     // Pass in the cursor to bind to.
                     new String[] {MySQLiteHelper.COLUMN_ID, MySQLiteHelper.COLUMN_MESSAGE}, // Array of cursor columns to bind to.
                     new int[] {android.R.id.text1, android.R.id.text2});  // Parallel array of which template objects to bind to those columns.
             // Bind to our new adapter.
             setListAdapter(adapter);
    }
    @Override
    public void onResume() {
        datasource.open();
        super.onResume();
      }

      @Override
    public void onPause() {
        datasource.close();
        super.onPause();
      }

Datasource和Mysqlitehelper是我的类名。MySqliteHelper类创建id和notes两列。Logcat是:

03-19 01:15:32.557: E/AndroidRuntime(10579): FATAL EXCEPTION: main
03-19 01:15:32.557: E/AndroidRuntime(10579): java.lang.RuntimeException: Unable to start activity ComponentInfo{soft.b.notes/soft.b.notes.NotesList}: java.lang.NullPointerException
03-19 01:15:32.557: E/AndroidRuntime(10579):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
03-19 01:15:32.557: E/AndroidRuntime(10579):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
03-19 01:15:32.557: E/AndroidRuntime(10579):    at android.app.ActivityThread.access$600(ActivityThread.java:122)
03-19 01:15:32.557: E/AndroidRuntime(10579):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
03-19 01:15:32.557: E/AndroidRuntime(10579):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-19 01:15:32.557: E/AndroidRuntime(10579):    at android.os.Looper.loop(Looper.java:137)
03-19 01:15:32.557: E/AndroidRuntime(10579):    at android.app.ActivityThread.main(ActivityThread.java:4340)

Answer 1

您的database未初始化。

另外，检查完整的堆栈跟踪也很有用。在RuntimeException中嵌套了一个"由"引起的异常。在IDE中双击堆栈跟踪行将准确显示出现问题的代码行。

Answer 2

在null数据库上运行rawQuery。我没有看到你在任何地方为你的数据库变量获得sqliteddatabase。