子类按钮

Question

在尝试创建ClassCastException子类后尝试扩展Button类时，我得到MusicButton。我不是要覆盖背景，只添加一些额外的方法。我确信我正确地扩展了该类，因此这必须是与Android UI组件交互的特定内容。为什么会这样？

以下是我获得ClassCastException：

的行

bMusic = (MusicButton) findViewById(R.id.musicButton);

这是MusicButton类：

public class MusicButton extends Button implements MusicObserver {
MusicService musicService;

public MusicButton(Context context) {
    super(context);
}

/**
 * Because we use findViewById to obtain view elements, the service instance
 * variable has to be initialized here instead of constructor.
 * 
 * @param service
 */
public void setMusicService(MusicService musicService) {
    this.musicService = musicService;
    update();
}

public void update() {
    /** setMusicService should have been called */
    Assert.assertNotNull(musicService);

    if (musicService.isMusicPlaying()) {
        this.setText("Stop Music");
    } else {
        this.setText("Play Music");
    }
}

/**
 * This function does not update the text of the button even though it knows
 * the status of the music player becuase I want all music observers to be
 * updated consistently, regardless if they are the ones forcing the
 * notification to occurr
 */
public void buttonPressed() {
    Assert.assertNotNull(musicService);

    if (musicService.isMusicPlaying()) {
        musicService.pauseMusic();
    } else {
        musicService.playMusic();
    }
}
}

Answer 1

事实证明，我需要从Button类中覆盖一些构造函数，并对XML进行一些更改。

以下是我的Button子类的代码：

public MusicButton(Context context) {
        super(context);
    }

    public MusicButton(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MusicButton(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    //rest of code irrelevant.....

和XML：

        <view
            android:id="@+id/musicButton"
            style="@style/CustomTheme.View.Button"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="50"
            class="com.GameOfThrones.Trivia.ui.music.MusicButton"
            android:text="Start Music" />