在Android问题上播放带有MediaPlayer类的mp3

Question

我的代码出了什么问题？ 我有一个切换按钮，我想播放/停止一个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，但在模拟器/手机上它给了我一个例外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启动歌曲的错误。 但它并没有停止。 因此，当我点击toggleButton时，它会启动，当我再次点击时，它没有做任何事情，但在log cat上给我一个错误：

首次按下切换按钮并且歌曲开始正常时出错（但是出现此错误）：

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toggleButton并且歌曲应该停止时出错：

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

Answer 1

首先，我的分析：1。你没有在onCreate（）中初始化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，首先加载应用程序时间。
2.在第二次点击按钮时，你已经打过电话

mediaPlayer.release();

下次单击MediaPlayer State时的异常

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^^！ 有很多方法可以改进这个简单的应用程序，但是，我猜您可以通过查看Android开发人员的参考文档来查找:)

Answer 2

您是否尝试过在onCreate内部而不是在类体内部进行初始化？ 这将是最好的地方。

如果在onClick内部初始化，则会显示您显示的错误。 这是因为每次单击时都会创建一个新的MediaPlayer实例。

Answer 3

你的问题在于release()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;
}

根据您的预期结果，您可以通过几种不同的方式对其进行更改。 如果您只是想要播放/暂停，正如您所说，那么您只需要删除stop()和release()调用。 特别是release() 。 该调用将音频资源释放回系统，这意味着您需要先将其恢复到准备状态，然后才能再次使用它。

我强烈建议非常彻底地阅读此参考文档 。 MediaPlayer类相当复杂，当状态管理不当时，这样的错误很容易出现。