android sqlite中的NullPointerException [重复]

Question

我正在尝试创建一个获取字符串值并返回名称中包含关键字的项目的字符串数组的操作。

这是我的代码：

public String[] getList(String st) {

   SQLiteDatabase database = myDBHelper.getReadableDatabase();

   String query = "Select * from " + TASKS_TABLE + " WHERE name LIKE '%" + st + "%'";
   Cursor cursor = database.rawQuery(query,null);
   //String[] columns = {TASK_IMAGE};
   // cursor = database.query(TASKS_TABLE,columns, TASK_NAME + "='" + st + "'",null, null, null, null, null);
   String[] array = new String[cursor.getCount()];
   int i = 0;
   while(cursor.moveToNext()){
       String uname = cursor.getString(cursor.getColumnIndex("name"));
       array[i] = uname;
       i++;
   }

   return array;
}

当我运行它时，我得到：

05-08 18:18:28.353 6637-6637/? E/AndroidRuntime: FATAL EXCEPTION: main
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime: Process: com.sahar.wave,   PID: 6637
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sahar.wave/com.sahar.wave.Results}: java.lang.NullPointerException
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:136)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5001)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:515)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:  Caused by: java.lang.NullPointerException
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at com.sahar.wave.Results.onCreate(Results.java:26)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.Activity.performCreate(Activity.java:5231)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread.access$800(ActivityThread.java:135) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:136) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5001) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at  java.lang.reflect.Method.invoke(Method.java:515) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
05-08 18:18:28.353 6637-6637/? E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method) 

这是活动代码：

private SiteDBMngr dbMngr;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.results);

    String st = "c";//-------------------------------put here the search key

   // String[] sites = new String[2];
    String[] sites = dbMngr.getList(st);
    ListAdapter Adapter = new CustomAdapter(this, sites);
    ListView listView = (ListView) findViewById(R.id.sitesListView);
    listView.setAdapter(Adapter);

    listView.setOnItemClickListener(
            new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                }
            }
    );
}

Answer 1

您的 SiteDBMngr dbMngr 为空，您应该在执行 dbMngr.getList(st) 之前分配它；

      SiteDBMngr = new SiteDBMngr(this);

可能与What is a NullPointerException, and how do I fix it?重复