Question

我编写此代码是为了制作像应用

一样的音板

public class ButtonSoundActivity extends Activity implements OnClickListener {
    private Button buttons[];
    private MediaPlayer mediaPlayers[];

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);     
    }

    @Override
    protected void onPause() {
        super.onPause();
        releaseSounds();
    }

    @Override
    protected void onResume() {
        super.onResume();
        initContent();
    }

    @Override
    protected void onStop() {
        super.onStop();
        releaseSounds();
    }

    /**
     * Initialise all the content :
     * buttons, media players and set click listeners for the buttons
     */
    private void initContent() {
        buttons = new Button[5];
        mediaPlayers = new MediaPlayer[5];

        buttons[0] = (Button)findViewById(R.id.button0);
        buttons[1] = (Button)findViewById(R.id.button1);
        buttons[2] = (Button)findViewById(R.id.button2);
        buttons[3] = (Button)findViewById(R.id.button3);
        buttons[4] = (Button)findViewById(R.id.button4);

        mediaPlayers[0] = MediaPlayer.create(ButtonSoundActivity.this, R.raw.sound1);
        mediaPlayers[1] = MediaPlayer.create(ButtonSoundActivity.this, R.raw.sound2);
        mediaPlayers[2] = MediaPlayer.create(ButtonSoundActivity.this, R.raw.sound3);
        mediaPlayers[3] = MediaPlayer.create(ButtonSoundActivity.this, R.raw.sound4);
        mediaPlayers[4] = MediaPlayer.create(ButtonSoundActivity.this, R.raw.sound5);


        for(int i=0; i<5; i++) {
            buttons[i].setOnClickListener(this);
        }      
    }

    public void onClick(View v) {
        stopSounds();
        for(int i=0; i<5; i++)
            if(v.getId() == buttons[i].getId()) {
                if(mediaPlayers[i] != null)
                mediaPlayers[i].start();
            }
    }

    /**
     * Stop the previous sound when another button is clicked
     * so that the sounds don't overlap
     */
    private void stopSounds() {
        for(int i=0; i<5 ;i++)
            if(mediaPlayers[i] != null)
            if(mediaPlayers[i].isPlaying()) {
                mediaPlayers[i].pause();
                mediaPlayers[i].seekTo(0);
            }
    }

    /**
     * Release all sounds and empty the mediaPlayers array
     */
    private void releaseSounds() {
        for(int i=0; i<5;i++) {
            if(mediaPlayers[i] != null) {
                mediaPlayers[i].stop();
                mediaPlayers[i].release();
                mediaPlayers[i] = null;                 
            }
        }
    }       
}

xml文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <Button android:layout_width="wrap_content" android:layout_height="wrap_content"
        android:text="button0" android:id="@+id/button0"/>

    <Button android:layout_width="wrap_content" android:layout_height="wrap_content"
        android:text="button1" android:id="@+id/button1"/>

    <Button android:layout_width="wrap_content" android:layout_height="wrap_content"
        android:text="button2" android:id="@+id/button2"/>      

    <Button android:layout_width="wrap_content" android:layout_height="wrap_content"
        android:text="button3" android:id="@+id/button3"/>

    <Button android:layout_width="wrap_content" android:layout_height="wrap_content"
        android:text="button4" android:id="@+id/button4"/>      
</LinearLayout>

问题在于，如果我连续多次单击一个按钮，声音不再播放，或者有时，当我第一次打开应用程序时，它会在我单击按钮时崩溃。该错误表明它与stopSounds方法

有关

error code

那么，有人有答案吗？

编辑：我在每个mediaPlayer元素之前添加了if（）来检查它们是否为null，我也遵循了这个方法：

            AssetFileDescriptor fileDescriptor = getResources().openRawResourceFd(R.raw.sound1);
        mediaPlayers[0] = new MediaPlayer();

        try {
            mediaPlayers[0].setDataSource(fileDescriptor.getFileDescriptor());
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (IllegalStateException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            mediaPlayers[0].prepare();
        } catch (IllegalStateException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

但没有任何运气:(

编辑2 ：我得到了它的工作:)，当我重新启动时，我只需要确保 mediaPlayer数组为空应用程序。我还添加了 onPause（）和 onResume（）函数。

Answer 1

您在NullPointerException方法中的第57行获得stopSounds。你可以自己发布这条线吗？

mediaPlayers中的一个对象很可能为null。尝试单步执行调试器，看看第一次输入stopSounds方法时数组的样子。

单击按钮时应用程序崩溃

1 个答案: