nullpointerexception - 如何获取 Spinner List 所选项目文本并用该值填充 android 中的 EditText

Question

当我尝试在选择监听器的 Itemselected 函数中获取 EditText 对象时，该行抛出 NullPointerException

<resources>
<string-array name="gender">
    <item name="Male">Male</item>
    <item name="Female">Female</item>
</string-array>
</resources>

布局

<EditText
    android:id="@+id/answer"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textview1"
    android:layout_below="@+id/textview1"
    android:ems="10"
    android:hint="answer" >

    <requestFocus />
</EditText>

<Spinner
    android:id="@+id/spinner1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/answer"
    android:layout_below="@+id/answer"
    android:layout_marginTop="22dp"
    android:entries="@array/gender"
    android:prompt="@string/spin_prompt" />

主要 Activity

public class MenuActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_menu);

    Spinner sp= (Spinner) findViewById(R.id.spinner1);
    sp.setOnItemSelectedListener(new SpinnerActivity());

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu, menu);
    return true;
}


}

旋转器 Activity

public class SpinnerActivity extends Activity implements OnItemSelectedListener{

 public void onItemSelected(AdapterView<?> parent, View view, 
            int pos, long id) {

                String selec = (parent.getItemAtPosition(pos)).toString();

                EditText ans= (EditText) findViewById(R.id.answer); 
                //NullPointerException at the time of retrieving EditText object 

                ans.setText(selec);
    }

    public void onNothingSelected(AdapterView<?> parent) {
        // Another interface callback
    }

}

Log-Cat 错误条目

03-21 17:23:42.232: E/AndroidRuntime(4019): FATAL EXCEPTION: main
03-21 17:23:42.232: E/AndroidRuntime(4019): java.lang.NullPointerException
03-21 17:23:42.232: E/AndroidRuntime(4019):     at android.app.Activity.findViewById(Activity.java:1853)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at com.practice.menu.SpinnerActivity.onItemSelected(SpinnerActivity.java:19)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at android.widget.AdapterView.fireOnSelected(AdapterView.java:892)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at android.widget.AdapterView.access$200(AdapterView.java:49)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:860)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at android.os.Handler.handleCallback(Handler.java:730)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at android.os.Handler.dispatchMessage(Handler.java:92)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at android.os.Looper.loop(Looper.java:137)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at android.app.ActivityThread.main(ActivityThread.java:5103)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at java.lang.reflect.Method.invokeNative(Native Method)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at java.lang.reflect.Method.invoke(Method.java:525)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-21 17:23:42.232: E/AndroidRuntime(4019):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

这里:

sp.setOnItemSelectedListener(new SpinnerActivity());

您正在尝试实例化另一个 Activity ，并尝试将其设置为监听器。这是行不通的，因为 Android Activity 不喜欢显式实例化它。

尝试为您的微调器实现监听器，如下所示:

    sp.setOnItemSelectedListener(new OnItemSelectedListener() {

        @Override
        public void onItemSelected(AdapterView<?> arg0, View arg1,
                int arg2, long arg3) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onNothingSelected(AdapterView<?> arg0) {
            // TODO Auto-generated method stub

        }

    });

您不再需要 SpinnerActivity