安卓简单mediaplayer简单应用源码分析

一、android studio文件夹介绍

文件夹列表

• manifests
  AndroidManifest.xml配置文件目录.主要工作有以下：
  1. 为应用的java软件包命名。软件包名称充当应用的唯一标识符。
  2. 描述应用的各个组件，包括构成应用的 Activity、服务、广播接收器和内容提供程序。它还为实现每个组件的类命名并发布其功能，例如它们可以处理的Intent消息。这些声明向 Android 系统告知有关组件以及可以启动这些组件的条件的信息.
  3. 确定托管应用组件的进程
  4. 声明应用必须具备哪些权限才能访问 API 中受保护的部分并与其他应用交互。还声明其他应用与该应用组件交互所需具备的权限.
  5. 列出 Instrumentation 类，这些类可在应用运行时提供分析和其他信息。这些声明只会在应用处于开发阶段时出现在清单中，在应用发布之前将移除。
  6. 声明应用所需的最低Android API级别
  7. 列出应用必须链接到的库
• java
  源码目录，逻辑处理文件夹
• res
  资源文件夹.
  layout - 布局文件
  drawable - 图片文件
  values - 值文件 包含一些string资源。
• generatedJava
  生成文件
• Gradle Scripts

二、布局文件解析

    >”
        android:id="@+id/button_rewind"    //添加id button_rewind
        android:layout_marginLeft="60dp"
        android:layout_marginStart="60dp"
        android:layout_marginTop="81dp"
        android:layout_below="@+id/textView_currentPosion"    //位于textView_currentPosion id的下方。
        android:layout_alignParentLeft="true"    //将控件的左边缘和父控件的左边缘对齐
        android:layout_alignParentStart="true"
        android:onClick="doRewind" />    //定义点击入口函数

    

    

    

    

    

    

三、源码文件解析

package com.example.mediaplayer;

import android.media.MediaPlayer;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.SeekBar;
import android.widget.TextView;

import java.util.concurrent.TimeUnit;

public class MainActivity extends AppCompatActivity {

    private TextView textMaxTime;
    private TextView textCurrentPosition;
    private Button buttonPause;
    private Button buttonStart;
    private SeekBar seekBar;
    private Handler threadHandler = new Handler();

    private MediaPlayer mediaPlayer;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d("MAIN ACTIVITY","start activity!");
        this.textCurrentPosition = this.findViewById(R.id.textView_currentPosion);
        this.textMaxTime= this.findViewById(R.id.textView_maxTime);
        this.buttonStart= this.findViewById(R.id.button_start);
        this.buttonPause= this.findViewById(R.id.button_pause);

        this.buttonPause.setEnabled(false);

        this.seekBar= this.findViewById(R.id.seekBar);
        this.seekBar.setClickable(false);

        // ID of  in 'raw' folder.
        int songId = this.getRawResIdByName("jinzhiwen");

        // Create MediaPlayer.
        this.mediaPlayer=   MediaPlayer.create(this, songId);
    }

    // Find ID of resource in 'raw' folder.
    public int getRawResIdByName(String resName)  {
        String pkgName = this.getPackageName();
        // Return 0 if not found.
        int resID = this.getResources().getIdentifier(resName, "raw", pkgName);
        return resID;
    }

    // Convert millisecond to string.
    private String millisecondsToString(int milliseconds)  {
        long minutes = TimeUnit.MILLISECONDS.toMinutes((long) milliseconds);
        long seconds =  TimeUnit.MILLISECONDS.toSeconds((long) milliseconds) ;
        return minutes+":"+ seconds;
    }


    public void doStart(View view)  {
        // The duration in milliseconds
        int duration = this.mediaPlayer.getDuration();

        int currentPosition = this.mediaPlayer.getCurrentPosition();
        if(currentPosition== 0)  {
            this.seekBar.setMax(duration);
            String maxTimeString = this.millisecondsToString(duration);
            this.textMaxTime.setText(maxTimeString);
        } else if(currentPosition== duration)  {
            // Resets the MediaPlayer to its uninitialized state.
            this.mediaPlayer.reset();
        }
        this.mediaPlayer.start();
        // Create a thread to update position of SeekBar.
        UpdateSeekBarThread updateSeekBarThread= new UpdateSeekBarThread();
        threadHandler.postDelayed(updateSeekBarThread,50);

        this.buttonPause.setEnabled(true);
        this.buttonStart.setEnabled(false);
    }

    // Thread to Update position for SeekBar.
    class UpdateSeekBarThread implements Runnable {

        public void run()  {
            int currentPosition = mediaPlayer.getCurrentPosition();
            String currentPositionStr = millisecondsToString(currentPosition);
            textCurrentPosition.setText(currentPositionStr);

            seekBar.setProgress(currentPosition);
            // Delay thread 50 milisecond.
            threadHandler.postDelayed(this, 50);
        }
    }

    // When user click to "Pause".
    public void doPause(View view)  {
        this.mediaPlayer.pause();
        this.buttonPause.setEnabled(false);
        this.buttonStart.setEnabled(true);
    }

    // When user click to "Rewind".
    public void doRewind(View view)  {
        int currentPosition = this.mediaPlayer.getCurrentPosition();
        int duration = this.mediaPlayer.getDuration();
        // 5 seconds.
        int SUBTRACT_TIME = 5000;

        if(currentPosition - SUBTRACT_TIME > 0 )  {
            this.mediaPlayer.seekTo(currentPosition - SUBTRACT_TIME);
        }
    }

    // When user click to "Fast-Forward".
    public void doFastForward(View view)  {
        int currentPosition = this.mediaPlayer.getCurrentPosition();
        int duration = this.mediaPlayer.getDuration();
        // 5 seconds.
        int ADD_TIME = 5000;

        if(currentPosition + ADD_TIME < duration)  {
            this.mediaPlayer.seekTo(currentPosition + ADD_TIME);
        }
    }
}