Java 来自数据库的微调器-首先添加空值

我有密码：

public class TesterActivity extends Activity {
public Context mContext;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // just for this example:
    // create database table with an id field and a text field and add some data
    class MyDBHelper extends SQLiteOpenHelper {
        public MyDBHelper(Context context) {
            super(context, "someDB", null, 2);
        }
        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL("CREATE TABLE someTable (someIDF INTEGER, someTextF TEXT)");
        }
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS someTable");
            onCreate(db);
            db.execSQL("INSERT INTO someTable (someIDF, someTextF) VALUES (54, 'Some text')");
            db.execSQL("INSERT INTO someTable (someIDF, someTextF) VALUES (99, 'Some more text')");
            db.execSQL("INSERT INTO someTable (someIDF, someTextF) VALUES (173, 'Even more text')");
        }
    }
    SQLiteDatabase db = new MyDBHelper(this).getWritableDatabase();

    // get a cursor from the database with an "_id" field
    Cursor c = db.rawQuery("SELECT someIDF AS _id, someTextF FROM someTable", null);

    // make an adapter from the cursor
    String[] from = new String[] {"someTextF"};
    int[] to = new int[] {android.R.id.text1};
    SimpleCursorAdapter sca = new SimpleCursorAdapter(this, android.R.layout.simple_spinner_item, c, from, to);

    // set layout for activated adapter
    sca.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 

    // get xml file spinner and set adapter 
    Spinner spin = (Spinner) this.findViewById(R.id.spinner1);
    spin.setAdapter(sca);

    // set spinner listener to display the selected item id
    mContext = this;
    spin.setOnItemSelectedListener(new OnItemSelectedListener() {
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id){
            Toast.makeText(mContext, "Selected ID=" + id, Toast.LENGTH_LONG).show();
        }
        public void onNothingSelected(AdapterView<?> parent) {}
        });
    }
}

显示微调器中的空值，但如果我想通过

TextView textView = (TextView)spinner.getSelectedView();
String result = textView.getText().toString();

我有一个错误：

java.lang.NullPointerException

如果我选择了非空项，则此错误始终存在

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为什么?？我可以用其他方法添加空值，但什么呢？

首先，我看不出您是否在activity onCreate方法（（textview）findbyid（R.id.etc.）上定义了textview？如果这个可以的话

在spin.setOnItemSelectedListener上，您可以使用：

String result = parent.getItemAtPosition(position).toString();

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结果应该是“”。

谢谢，但我想在这个方法之外得到这个值，如果他没有改变的话。那么为什么要使用静态字符串值来得到它呢

String result = parent.getItemAtPosition(position).toString();