Question

我正在尝试使用Cursor从表中检索一些数据，以便在TextView中显示它，但是我收到了一个错误。

请小心帮助我。
这是我的代码

public class DisplayBudget extends AppCompatActivity implements  View.OnClickListener {
  SQLiteDatabase db;
  TextView bname,name,limit;
  Button del;
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.budget_details);
    bname = (TextView) findViewById(R.id.textViewbname);
    name = (TextView) findViewById(R.id.textViewname);
    limit = (TextView) findViewById(R.id.textViewlimit);
    del = (Button) findViewById(R.id.button2);
    del.setOnClickListener(this);
    DBController dbController = new DBController(this);
    dbController.openToDisplay();
    Cursor cursor = db.rawQuery(" select *from "+DBHelper.TABLE_NAME+ " where id = 1 ",null);
    cursor.moveToFirst();
    name.append(cursor.getString(cursor.getColumnIndex(DBHelper.OWNER_NAME)));
    bname.append(cursor.getString(cursor.getColumnIndex(DBHelper.BUDGET_NAME)));
    limit.append(cursor.getString(cursor.getColumnIndex(DBHelper.BUDGET_LIMIT)));
    cursor.close();
}

这是LogCat

12-25 00:39:46.440  30123-30123/com.example.rajkumar.budget W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xb0d40b20)
12-25 00:39:46.440  30123-30123/com.example.rajkumar.budget E/AndroidRuntime﹕    FATAL EXCEPTION: main
Process: com.example.rajkumar.budget, PID: 30123
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.rajkumar.budget/com.example.rajkumar.budget.DisplayBudget}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
        at android.app.ActivityThread.access$800(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5001)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at com.example.rajkumar.budget.DisplayBudget.onCreate(DisplayBudget.java:28)
        at android.app.Activity.performCreate(Activity.java:5231)

Answer 1

您获得了NPE，因为<{1}}位于

db=null

您初始化 db 的位置？对于未来的问题，也请参考Cursor cursor = db.rawQuery(" select * from "+DBHelper.TABLE_NAME+ " where id = 1 ",null);回答。

Answer 2

在* and from之间占用空间，以便您的查询看起来像

Cursor cursor = db.rawQuery("select * from "+DBHelper.TABLE_NAME+ " where id = 1 ",null);

Answer 3

你只是改变了，所以你不能得到错误： -

String dataquery =＆＃34;从表名中选择*，其中id =＆＃34; + ID; 的

的

光标游标= db.rawQuery（dataquery，null）;

有用的

Answer 4

试试这个。

DBController dbController = new DBController(this);
    SQLiteDatabase db = createDatabase.open();
 Cursor cursor = db.rawQuery(" select * from "+DBHelper.TABLE_NAME+ " where id = 1 ",null);
if(cursor.moveToFirst()){
 name.append(cursor.getString(cursor.getColumnIndex(DBHelper.OWNER_NAME)));
     bname.append(cursor.getString(cursor.getColumnIndex(DBHelper.BUDGET_NAME)));
    limit.append(cursor.getString(cursor.getColumnIndex(DBHelper.BUDGET_LIMIT)));     }

使用Cursor检索数据时出现NullPointerException

4 个答案: