按钮的setOnClickListener不起作用

时间:2014-05-27 00:35:20

标签: java android eclipse listener

public class QuizActivity extends ActionBarActivity {

private Button mTrueButton; 
private Button mFalseButton; 

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

    mTrueButton = (Button)findViewById(R.id.true_button);
   mTrueButton.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {
        Toast.makeText(QuizActivity.this, R.string.false_toast, Toast.LENGTH_SHORT).show(); 

    }
});

    mFalseButton = (Button)findViewById(R.id.false_button); 
    mFalseButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Toast.makeText(QuizActivity.this, R.string.false_toast, Toast.LENGTH_SHORT).show(); 
        }
    });

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }
}

当我在没有mTrueButton.setOnClickListener和mTrueButton.setOnClickListener的情况下注释掉代码部分时,模拟器能够显示按钮。但是,当我将它们放回时,即使没有任何方法在onClick(View v)中,模拟器也会告诉我QuizApp已停止。导入语句没有任何问题,因为我使用了命令+ shift + o。有谁知道为什么它不工作?

这是fragment_quiz.xml类:

<LinearLayout xmlns:android = "http://schemas.android.com/apk/res/android"
android:layout_width = "match_parent"
android:layout_height = "match_parent"
android:gravity = "center"
android:orientation = "vertical" >

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:padding="24dp"
    android:text="@string/question_text" />

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center"> 
    <Button
        android:id="@+id/true_button"
        android:orientation="horizontal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/true_button" />

    <Button
        android:id = "@+id/false_button"
        android:orientation="horizontal"
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:text = "@string/false_button" />

 </LinearLayout>

</LinearLayout>

以下是LogCat的前几行给我的内容:

FATAL EXCEPTION: main
Process: com.example.geoquiz, PID: 1099
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.geoquiz/com.example.geoquiz.QuizActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)

1 个答案:

答案 0 :(得分:2)

在您的代码中使用

设置内容视图
activity_quiz

并且您说您发布的xml称为

fragment_quiz

你得到一个空指针异常,因为你定义的按钮不在activity_quiz