Android 简明教程

Android - MediaPlayer

Android 提供了许多控制音频/视频文件和流回放的方法。其中一种方法是通过一个名为 MediaPlayer 的类。

Android provides many ways to control playback of audio/video files and streams. One of this way is through a class called MediaPlayer.

Android 提供 MediaPlayer 类以访问内建媒体播放器服务，如播放音频、视频等。为了使用 MediaPlayer，我们必须调用此类的静态方法 create() 。此方法返回一个 MediaPlayer 类实例。其语法如下：

Android is providing MediaPlayer class to access built-in mediaplayer services like playing audio,video e.t.c. In order to use MediaPlayer, we have to call a static Method create() of this class. This method returns an instance of MediaPlayer class. Its syntax is as follows −

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

第二个参数是要播放的歌曲的名称。你必须在项目中创建一个名为 raw 的新文件夹，并将音乐文件放置其中。

The second parameter is the name of the song that you want to play. You have to make a new folder under your project with name raw and place the music file into it.

一旦你创建了 Mediaplayer 对象，就可以调用一些方法来启动或停止音乐。下面列出这些方法。

Once you have created the Mediaplayer object you can call some methods to start or stop the music. These methods are listed below.

mediaPlayer.start();
mediaPlayer.pause();

调用 start() 方法后，音乐会从头开始播放。如果在 pause() 方法后再次调用此方法，音乐将从它停止的地方开始播放，而不是从头开始播放。

On call to start() method, the music will start playing from the beginning. If this method is called again after the pause() method, the music would start playing from where it is left and not from the beginning.

为了从头开始播放音乐，你必须调用 reset() 方法。其语法如下。

In order to start music from the beginning, you have to call reset() method. Its syntax is given below.

mediaPlayer.reset();

除了开始和暂停方法之外，此类还提供了用于更好地处理音频/视频文件的方法。下面列出这些方法：

Apart from the start and pause method, there are other methods provided by this class for better dealing with audio/video files. These methods are listed below −

Sr.No	Method & description
1	isPlaying() This method just returns true/false indicating the song is playing or not
2	seekTo(position) This method takes an integer, and move song to that particular position millisecond
3	getCurrentPosition() This method returns the current position of song in milliseconds
4	getDuration() This method returns the total time duration of song in milliseconds
5	reset() This method resets the media player
6	release() This method releases any resource attached with MediaPlayer object
7	setVolume(float leftVolume, float rightVolume) This method sets the up down volume for this player
8	setDataSource(FileDescriptor fd) This method sets the data source of audio/video file
9	selectTrack(int index) This method takes an integer, and select the track from the list on that particular index
10	getTrackInfo() This method returns an array of track information

Example

以下是演示 MediaPlayer 类使用的一个示例。它创建一个基本的媒体播放器，允许你一首歌曲的前进、后退、播放和暂停。

Here is an example demonstrating the use of MediaPlayer class. It creates a basic media player that allows you to forward, backward, play and pause a song.

要体验此示例，你需在实际设备中运行它才能听到音频。

To experiment with this example, you need to run this on an actual device to hear the audio sound.

Steps	Description
1	You will use Android studio IDE to create an Android application under a package com.example.sairamkrishna.myapplication.
2	Modify src/MainActivity.java file to add MediaPlayer code.
3	Modify the res/layout/activity_main to add respective XML components
4	Create a new folder under MediaPlayer with name as raw and place an mp3 music file in it with name as song.mp3
5	Run the application and choose a running android device and install the application on it and verify the results

以下是修改的主活动文件 src/MainActivity.java 的内容。

Following is the content of the modified main activity file src/MainActivity.java.

package com.example.sairamkrishna.myapplication;

import android.app.Activity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;

import android.widget.Button;
import android.widget.ImageView;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.Toast;
import java.util.concurrent.TimeUnit;


public class MainActivity extends Activity {
   private Button b1,b2,b3,b4;
   private ImageView iv;
   private MediaPlayer mediaPlayer;

   private double startTime = 0;
   private double finalTime = 0;

   private Handler myHandler = new Handler();;
   private int forwardTime = 5000;
   private int backwardTime = 5000;
   private SeekBar seekbar;
   private TextView tx1,tx2,tx3;

   public static int oneTimeOnly = 0;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);

      b1 = (Button) findViewById(R.id.button);
      b2 = (Button) findViewById(R.id.button2);
      b3 = (Button)findViewById(R.id.button3);
      b4 = (Button)findViewById(R.id.button4);
      iv = (ImageView)findViewById(R.id.imageView);

      tx1 = (TextView)findViewById(R.id.textView2);
      tx2 = (TextView)findViewById(R.id.textView3);
      tx3 = (TextView)findViewById(R.id.textView4);
      tx3.setText("Song.mp3");

      mediaPlayer = MediaPlayer.create(this, R.raw.song);
      seekbar = (SeekBar)findViewById(R.id.seekBar);
      seekbar.setClickable(false);
      b2.setEnabled(false);

      b3.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            Toast.makeText(getApplicationContext(), "Playing
               sound",Toast.LENGTH_SHORT).show();
            mediaPlayer.start();

            finalTime = mediaPlayer.getDuration();
            startTime = mediaPlayer.getCurrentPosition();

            if (oneTimeOnly == 0) {
               seekbar.setMax((int) finalTime);
               oneTimeOnly = 1;
            }

            tx2.setText(String.format("%d min, %d sec",
               TimeUnit.MILLISECONDS.toMinutes((long) finalTime),
               TimeUnit.MILLISECONDS.toSeconds((long) finalTime) -
               TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes((long)
                  finalTime)))
            );

            tx1.setText(String.format("%d min, %d sec",
               TimeUnit.MILLISECONDS.toMinutes((long) startTime),
               TimeUnit.MILLISECONDS.toSeconds((long) startTime) -
               TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes((long)
                  startTime)))
            );

            seekbar.setProgress((int)startTime);
            myHandler.postDelayed(UpdateSongTime,100);
            b2.setEnabled(true);
            b3.setEnabled(false);
         }
      });

      b2.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            Toast.makeText(getApplicationContext(), "Pausing
               sound",Toast.LENGTH_SHORT).show();
            mediaPlayer.pause();
            b2.setEnabled(false);
            b3.setEnabled(true);
         }
      });

      b1.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            int temp = (int)startTime;

            if((temp+forwardTime)<=finalTime){
               startTime = startTime + forwardTime;
               mediaPlayer.seekTo((int) startTime);
               Toast.makeText(getApplicationContext(),"You have Jumped forward 5
                  seconds",Toast.LENGTH_SHORT).show();
            }else{
               Toast.makeText(getApplicationContext(),"Cannot jump forward 5
                  seconds",Toast.LENGTH_SHORT).show();
            }
         }
      });

      b4.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            int temp = (int)startTime;

            if((temp-backwardTime)>0){
               startTime = startTime - backwardTime;
               mediaPlayer.seekTo((int) startTime);
               Toast.makeText(getApplicationContext(),"You have Jumped backward 5
                  seconds",Toast.LENGTH_SHORT).show();
            }else{
               Toast.makeText(getApplicationContext(),"Cannot jump backward 5
                  seconds",Toast.LENGTH_SHORT).show();
            }
         }
      });
   }

   private Runnable UpdateSongTime = new Runnable() {
      public void run() {
         startTime = mediaPlayer.getCurrentPosition();
         tx1.setText(String.format("%d min, %d sec",
            TimeUnit.MILLISECONDS.toMinutes((long) startTime),
            TimeUnit.MILLISECONDS.toSeconds((long) startTime) -
            TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.
            toMinutes((long) startTime)))
         );
         seekbar.setProgress((int)startTime);
         myHandler.postDelayed(this, 100);
      }
   };
}

以下是修改后的 xml res/layout/activity_main.xml 内容。

Following is the modified content of the xml res/layout/activity_main.xml.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:paddingLeft="@dimen/activity_horizontal_margin"
   android:paddingRight="@dimen/activity_horizontal_margin"
   android:paddingTop="@dimen/activity_vertical_margin"
   android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

   <TextView android:text="Music Palyer" android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/textview"
      android:textSize="35dp"
      android:layout_alignParentTop="true"
      android:layout_centerHorizontal="true" />

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Tutorials point"
      android:id="@+id/textView"
      android:layout_below="@+id/textview"
      android:layout_centerHorizontal="true"
      android:textColor="#ff7aff24"
      android:textSize="35dp" />

   <ImageView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/imageView"
      android:layout_below="@+id/textView"
      android:layout_centerHorizontal="true"
      android:src="@drawable/abc"/>

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/forward"
      android:id="@+id/button"
      android:layout_alignParentBottom="true"
      android:layout_alignParentLeft="true"
      android:layout_alignParentStart="true" />

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/pause"
      android:id="@+id/button2"
      android:layout_alignParentBottom="true"
      android:layout_alignLeft="@+id/imageView"
      android:layout_alignStart="@+id/imageView" />

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/back"
      android:id="@+id/button3"
      android:layout_alignTop="@+id/button2"
      android:layout_toRightOf="@+id/button2"
      android:layout_toEndOf="@+id/button2" />

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/rewind"
      android:id="@+id/button4"
      android:layout_alignTop="@+id/button3"
      android:layout_toRightOf="@+id/button3"
      android:layout_toEndOf="@+id/button3" />

   <SeekBar
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/seekBar"
      android:layout_alignLeft="@+id/textview"
      android:layout_alignStart="@+id/textview"
      android:layout_alignRight="@+id/textview"
      android:layout_alignEnd="@+id/textview"
      android:layout_above="@+id/button" />

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:textAppearance="?android:attr/textAppearanceSmall"
      android:text="Small Text"
      android:id="@+id/textView2"
      android:layout_above="@+id/seekBar"
      android:layout_toLeftOf="@+id/textView"
      android:layout_toStartOf="@+id/textView" />

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:textAppearance="?android:attr/textAppearanceSmall"
      android:text="Small Text"
      android:id="@+id/textView3"
      android:layout_above="@+id/seekBar"
      android:layout_alignRight="@+id/button4"
      android:layout_alignEnd="@+id/button4" />

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:textAppearance="?android:attr/textAppearanceMedium"
      android:text="Medium Text"
      android:id="@+id/textView4"
      android:layout_alignBaseline="@+id/textView2"
      android:layout_alignBottom="@+id/textView2"
      android:layout_centerHorizontal="true" />

</RelativeLayout>

以下是 res/values/string.xml 的内容。

Following is the content of the res/values/string.xml.

<resources>
   <string name="app_name">My Application</string>
   <string name="back"><![CDATA[<]]></string>
   <string name="rewind"><![CDATA[<<]]></string>
   <string name="forward"><![CDATA[>>]]></string>
   <string name="pause">||</string>
</resources>

下面是 AndroidManifest.xml 文件的内容。

Following is the content of AndroidManifest.xml file.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.sairamkrishna.myapplication" >

   <application
      android:allowBackup="true"
      android:icon="@drawable/ic_launcher"
      android:label="@string/app_name"
      android:theme="@style/AppTheme" >

      <activity
         android:name="com.example.sairamkrishna.myapplication.MainActivity"
         android:label="@string/app_name" >

         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>

      </activity>

   </application>
</manifest>

让我们尝试运行你的应用程序。我假设你已将实际的 Android 移动设备连接至计算机。要通过 Eclipse 运行该应用，请打开项目的活动文件之一，然后单击工具栏中的运行图标。在 Android Studio 启动应用之前，Android Studio 将显示以下屏幕

Let’s try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from Eclipse, open one of your project’s activity files and click Run icon from the toolbar. Before starting your application, Android studio will display following screens

默认情况下，你应该会看到禁用状态的暂停按钮。现在，按下播放按钮，该播放按钮将变为禁用状态，暂停按钮变为启用状态。这在以下图片中显示为 −

By default you would see the pause button disabled. Now press play button and it would become disable and pause button become enable. It is shown in the picture below −

一直到目前为止，一直在播放音乐。现在按下暂停按钮，看看暂停通知。这在以下图片中显示为 −

Up till now, the music has been playing. Now press the pause button and see the pause notification. This is shown below −

现在当你再次按下播放按钮时，歌曲不会从头开始播放，而会从暂停的地方继续播放。现在按下快进或快退按钮，将歌曲向前或向后跳 5 秒。有一段时间歌曲无法向前跳。此时，会出现通知，内容类似于以下内容 −

Now when you press the play button again, the song will not play from the beginning but from where it was paused. Now press the fast forward or backward button to jump the song forward or backward 5 seconds. A time came when the song cannot be jump forward. At this point , the notification would appear which would be something like this −

当你正在移动设备中执行其他任务时，你的音乐会继续在后台播放。为了停止播放，你必须从后台活动中退出此应用程序。

Your music would remain playing in the background while you are doing other tasks in your mobile. In order to stop it , you have to exit this application from background activities.

以上图片显示了当你选择倒带按钮时的情形。

Above image shows when you pick rewind button.