java - 在 Android 问题上使用 MediaPlayer 类播放 mp3

Question

我的代码有什么问题？我有一个切换按钮，我想播放/停止 mp3。我猜代码应该如下：

package com.android.iFocus;


import android.app.Activity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ToggleButton;

public class iFocusActivity extends Activity implements OnClickListener {
    public int count;
    MediaPlayer mediaPlayer = MediaPlayer.create(this, R.raw.rain);

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ToggleButton toggleRain = (ToggleButton)findViewById(R.id.toggleRain);

        //Define Listeners
        toggleRain.setOnClickListener(this);

        count = 0;


    }


    @Override    
    public void onClick(View toggleRain) {


        if(count==0){

            mediaPlayer.start();
            count=1;
        } else {
            //MediaPlayer mediaPlayer = MediaPlayer.create(this, R.raw.rain);
                    mediaPlayer.pause();
            mediaPlayer.stop();
                    mediaPlayer.release();
            count=0;
        }

    }

}

问题是：Eclipse 没有给出任何错误，但是在模拟器/电话上它给了我一个异常并在启动后立即死亡。开始：

10-02 20:28:24.312: INFO/ActivityManager(59): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.android.iFocus/.iFocusActivity }
10-02 20:28:24.392: DEBUG/AndroidRuntime(960): Shutting down VM
10-02 20:28:24.402: DEBUG/dalvikvm(960): Debugger has detached; object registry had 1 entries
10-02 20:28:24.462: INFO/ActivityManager(59): Start proc com.android.iFocus for activity com.android.iFocus/.iFocusActivity: pid=967 uid=10036 gids={}
10-02 20:28:24.502: INFO/AndroidRuntime(960): NOTE: attach of thread 'Binder Thread #3' failed
10-02 20:28:25.822: DEBUG/AndroidRuntime(967): Shutting down VM
10-02 20:28:25.822: WARN/dalvikvm(967): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
10-02 20:28:25.932: ERROR/AndroidRuntime(967): FATAL EXCEPTION: main
10-02 20:28:25.932: ERROR/AndroidRuntime(967): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.android.iFocus/com.android.iFocus.iFocusActivity}: java.lang.NullPointerException

好吧，当我在 onClick 内部类中初始化 mediaPlayer 时，它不会给我任何错误，并且应用程序不会给我任何错误来启动歌曲。但它并没有停止。所以，当我点击toggleButton时，它会启动，当我再次点击时，它什么也没做，只是在日志猫上给我一个错误：

第一次按下切换按钮并且歌曲开始正常时出错（但给出此错误）：

10-02 20:39:02.712: INFO/ActivityManager(59): Start proc com.android.iFocus for activity com.android.iFocus/.iFocusActivity: pid=996 uid=10036 gids={}
10-02 20:39:02.782: INFO/AndroidRuntime(989): NOTE: attach of thread 'Binder Thread #3' failed
10-02 20:39:04.432: INFO/ActivityManager(59): Displayed activity com.android.iFocus/.iFocusActivity: 1804 ms (total 640049 ms)
10-02 20:39:08.672: DEBUG/AudioSink(34): bufferCount (4) is too small and increased to 12
10-02 20:39:08.982: WARN/AudioFlinger(34): write blocked for 73 msecs, 2105 delayed writes, thread 0xb3b8
10-02 20:39:09.682: DEBUG/dalvikvm(437): GC_EXPLICIT freed 686 objects / 38192 bytes in 216ms
10-02 20:39:14.502: WARN/AudioFlinger(34): write blocked for 86 msecs, 2110 delayed writes, thread 0xb3b8
10-02 20:39:14.642: DEBUG/dalvikvm(188): GC_EXPLICIT freed 164 objects / 11408 bytes in 176ms
10-02 20:39:19.622: DEBUG/dalvikvm(261): GC_EXPLICIT freed 43 objects / 1912 bytes in 154ms
10-02 20:39:20.352: WARN/AudioFlinger(34): write blocked for 78 msecs, 2119 delayed writes, thread 0xb3b8

当我再次按下切换按钮时出错，歌曲应该停止：

10-02 20:43:22.412: ERROR/MediaPlayer(1032): pause called in state 8
10-02 20:43:22.412: ERROR/MediaPlayer(1032): error (-38, 0)
10-02 20:43:22.412: ERROR/MediaPlayer(1032): stop called in state 0
10-02 20:43:22.412: ERROR/MediaPlayer(1032): error (-38, 0)
10-02 20:43:22.612: WARN/MediaPlayer(1032): mediaplayer went away with unhandled events
10-02 20:43:22.612: WARN/MediaPlayer(1032): mediaplayer went away with unhandled events
10-02 20:43:22.622: WARN/MediaPlayer(1032): mediaplayer went away with unhandled events
10-02 20:43:22.622: WARN/MediaPlayer(1032): mediaplayer went away with unhandled events

score 4 · Accepted Answer

首先，我的分析： 1.你没有在onCreate()里面初始化MediaPlayer：

MediaPlayer mediaPlayer = MediaPlayer.create(this, R.raw.rain);

'this' <--- 这个东西是 NULL，所以你在运行时有一个 NullPointerException，首先加载应用程序计时。
2. 在第二次点击按钮时，你已经调用了

mediaPlayer.release();

下次单击时，MediaPlayer State 出现异常

好吧，修复非常简单，您需要考虑 Android 编程的最佳实践：

package pete.android.study;

import android.app.Activity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ToggleButton;

public class Main extends Activity implements OnClickListener {
        // declare controls
        public int count = 0;
        MediaPlayer mediaPlayer = null;  
        ToggleButton toggleRain = null;
        /*
         * (non-Javadoc)
         * @see android.app.Activity#onCreate(android.os.Bundle)
         */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            // load layout
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
            // load controls
            toggleRain = (ToggleButton)findViewById(R.id.toggleRain);
            // init player
            mediaPlayer = MediaPlayer.create(this, R.raw.rain);
            // set click event handler
            toggleRain.setOnClickListener(this);
            // init state for playing
            count = 0;
        }

        /*
         * (non-Javadoc)
         * @see android.view.View.OnClickListener#onClick(android.view.View)
         */
        @Override    
        public void onClick(View toggleRain) {
            if(count == 0){
                mediaPlayer.start();
                count = 1;
            } else {
                mediaPlayer.pause();                
                count = 0;
            }
        }

        /*
         * (non-Javadoc)
         * @see android.app.Activity#onDestroy()
         */
        @Override
        protected void onDestroy() {
            if(mediaPlayer != null) {
                mediaPlayer.stop();
                mediaPlayer.release();
                mediaPlayer = null;
            }
        }

}

当然它就像魅力一样^^！有很多方法可以改进这个简单的应用程序，但是，我想您可以通过查看 Android 开发人员参考文档找到答案：)

score 0 · Accepted Answer

您是否尝试过将初始化移动到 onCreate 内部而不是仅在类主体内部？这将是最好的地方。

如果您在 onClick 内部进行初始化，则显示的错误是预期的。这是因为每次单击时都会创建一个新的 MediaPlayer 实例。

score 0 · Accepted Answer

您的问题在于release()此处的声明：

if(count==0){
    mediaPlayer.start();
    count = 1;
} else {
    //MediaPlayer mediaPlayer = MediaPlayer.create(this, R.raw.rain);
    mediaPlayer.pause();
    mediaPlayer.stop();
    mediaPlayer.release();
    count = 0;
}

根据您想要的结果，有几种不同的方法可以更改此设置。如果您只想播放/暂停，正如您所说，那么您只需要删除stop()andrelease()调用。特别是release()。该调用将音频资源释放回系统，这意味着您需要将其恢复到准备好的状态，然后才能再次使用它。

我强烈建议您非常彻底地阅读此参考文档。MediaPlayer 类相当复杂，当没有正确管理状态时，很容易出现这样的错误。

java - 在 Android 问题上使用 MediaPlayer 类播放 mp3

3 回答 3

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