java - 在 Activity 时实现后退按钮(物理)Android

Question

我正在尝试在 Android 应用程序上实现后退按钮。图像按钮工作正常(即它转到上一个屏幕并停止音乐。单击物理后退按钮会导致应用程序退出并出现错误。如何解决这个问题？下面是我当前的代码...

    package com.mellowbluestuff;

import java.util.concurrent.TimeUnit;

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

import java.util.List;

import com.example.android.searchabledict.R;
import com.mellowbluestuff.*;

import android.os.Bundle;
import android.os.Vibrator;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.MediaController.MediaPlayerControl;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.widget.Toast;


public class MusicPlayerA extends Activity {

    private MediaPlayer mediaPlayer;
    public TextView songName, duration;
    private double timeElapsed = 0, finalTime = 0;
    private int forwardTime = 2500, backwardTime = 2500;
    private Handler durationHandler = new Handler();
    private SeekBar seekbar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //set the layout of the Activity
        setContentView(R.layout.musicplayerview);
        //initialize views
        initializeViews();
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (mediaPlayer != null) {
            mediaPlayer.pause();
            if (isFinishing()) {
                mediaPlayer.stop();
                mediaPlayer.release();
            }
        }
    }

    public void initializeViews(){
        songName = (TextView) findViewById(R.id.songName);
        mediaPlayer = MediaPlayer.create(this, R.raw.druidsad);
        finalTime = mediaPlayer.getDuration();
        duration = (TextView) findViewById(R.id.songDuration);
        seekbar = (SeekBar) findViewById(R.id.seekBar);
        songName.setText("Druids Ad");  
        seekbar.setMax((int) finalTime);
        seekbar.setClickable(true);
    }

    // play mp3 song
    public void play(View view) {
        mediaPlayer.start();
        timeElapsed = mediaPlayer.getCurrentPosition();
        seekbar.setProgress((int) timeElapsed);
        durationHandler.postDelayed(updateSeekBarTime, 100);
    }

    //handler to change seekBarTime
    private Runnable updateSeekBarTime = new Runnable() {
        public void run() {
            //get current position
            timeElapsed = mediaPlayer.getCurrentPosition();
            //set seekbar progress
            seekbar.setProgress((int) timeElapsed);
            //set time remaining
            double timeRemaining = finalTime - timeElapsed;
            duration.setText(String.format("%d min, %d sec", TimeUnit.MILLISECONDS.toMinutes((long) timeRemaining), TimeUnit.MILLISECONDS.toSeconds((long) timeRemaining) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes((long) timeRemaining))));

            //repeat yourself that again in 100 miliseconds
            durationHandler.postDelayed(this, 100);
        }
    };

    // pause mp3 song
    public void pause(View view) {
        mediaPlayer.pause();
    }

    // go forward at forwardTime seconds
    public void forward(View view) {
        //check if we can go forward at forwardTime seconds before song endes
        if ((timeElapsed + forwardTime) <= finalTime) {
            timeElapsed = timeElapsed + forwardTime;

            //seek to the exact second of the track
            mediaPlayer.seekTo((int) timeElapsed);
        }
    }

    // go backwards at backwardTime seconds
    public void rewind(View view) {
        //check if we can go back at backwardTime seconds after song starts
        if ((timeElapsed - backwardTime) > 0) {
            timeElapsed = timeElapsed - backwardTime;

            //seek to the exact second of the track
            mediaPlayer.seekTo((int) timeElapsed);
        }
    }

     // handler for back button used on music player screen
     public void BackButton2 (View view) {

        MediaPlayer mMediaPlayer = MediaPlayer.create(this, R.raw.soundbackbutton) ;
        mMediaPlayer.start();

        Vibrator vib = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
        vib.vibrate(200);

        Intent mus = new Intent (this, Music.class);
        startActivity(mus);
     }

    // handler for home button used on all screens
    public void BackButton (View view) {

        MediaPlayer mMediaPlayer = MediaPlayer.create(this, R.raw.soundbackbutton) ;
        mMediaPlayer.start();

        Vibrator vib = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
        vib.vibrate(200);

        Intent mn = new Intent (this, Music.class);
        startActivity(mn);
     }

}

和 XML

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="center"
    android:background="@drawable/fabricblacksmr"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin" >

      <ImageButton
        android:id="@+id/BackButton2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="top"
        android:onClick="BackButton2"
        android:src="@drawable/buttonback"
        android:background="#00000000" />   

    <TextView
        android:id="@+id/songName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:paddingTop="4dp"
        android:text="songName" />

    <ImageView
        android:id="@+id/mp3Image"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:background="#00000000"
        android:paddingBottom="8dp"
        android:paddingTop="8dp"
        android:onClick="play"
        android:src="@drawable/anglo" />

        <TextView
            android:id="@+id/songDuration"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_marginBottom="5dp"
            android:layout_marginTop="5dp"
            android:text="Best enjoyed with stereo headphones" />

    <SeekBar
        android:id="@+id/seekBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="5dp" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="15dp"
        android:gravity="center_horizontal"
        android:orientation="horizontal" >

        <ImageButton
            android:id="@+id/media_rew"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="14dp"
            android:onClick="rewind"
            android:src="@android:drawable/ic_media_rew" />

        <ImageButton
            android:id="@+id/media_pause"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="14dp"
            android:onClick="pause"
            android:src="@android:drawable/ic_media_pause" />

        <ImageButton
            android:id="@+id/media_play"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="14dp"
            android:onClick="play"
            android:src="@android:drawable/ic_media_play" />

        <ImageButton
            android:id="@+id/media_ff"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="14dp"
            android:onClick="forward"
            android:src="@android:drawable/ic_media_ff" />
    </LinearLayout>

</LinearLayout>

Answer 1

用你的代码覆盖 onBackPressed() ，如下所示:

@Override
public void onBackPressed() {
  Your code
}