我是想弄一個播放音樂的app
可以有播放暫停等功能
另外還可以觸發seekbar達成控制音樂播放等效果
可是一運行app就出錯
錯誤警示,
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.SeekBar.setOnSeekBarChangeListener(android.widget.SeekBar$OnSeekBarChangeListener)' on a null object reference
at com.example.user.lab2_leemingchak.MainActivity.onCreate(MainActivity.java:43)
package com.example.user.lab2_leemingchak;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.net.Uri;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.ProgressBar;
import android.widget.SeekBar;
public class MainActivity extends AppCompatActivity implements MediaPlayer.OnPreparedListener,
MediaPlayer.OnCompletionListener {
private MediaPlayer mediaplayer;
private SeekBar seekbar;
private Runnable runnable;
private Handler handble;
private int i;
ImageButton playbtn, stopbtn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//initialize button UIs
playbtn = (ImageButton) findViewById(R.id.playBtn);
stopbtn = (ImageButton) findViewById(R.id.stopBtn);
//convert String url to Uri format using .parse()
Uri path = Uri.parse("android.resource://" + //set the music file in res/raw as default
getPackageName() + "/" + R.raw.enm);
//disable the Play and Stop buttons using .setEnabled()
playbtn.setEnabled(false);
stopbtn.setEnabled(false);
//new a MediaPlayer object
mediaplayer = new MediaPlayer();
//set OnPreparedListener() and OnCompletionListener() to the MediaPlayer object
mediaplayer.setOnPreparedListener(this);
mediaplayer.setOnCompletionListener(this);
seekbar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
i = progress;
if (fromUser) {
mediaplayer.seekTo(progress);
}
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
}
});
//prepare and download the audio file, onPrepared() method will be run when ready to play
try {
mediaplayer.reset();
mediaplayer.setDataSource(this, path);
mediaplayer.setAudioStreamType(AudioManager.STREAM_MUSIC); //in streaming mode
mediaplayer.prepareAsync();
} catch (Exception e) {
e.printStackTrace();
}
seekbar = (SeekBar) findViewById(R.id.seekBar);
}
// when Play/Pause button is clicked
// check whether the MediaPlayer is playing or not, start playing if not, otherwise, pause the playback
public void onPlayUrlClick(View view) {
if (mediaplayer.isPlaying()) {
mediaplayer.pause();
playbtn.setEnabled(true);
stopbtn.setEnabled(true);
playbtn.setImageResource(R.drawable.play);
} else {
mediaplayer.start();
playbtn.setEnabled(true);
stopbtn.setEnabled(true);
playbtn.setImageResource(R.drawable.puase);
changeSeekbar();
}
}
// when Stop button is clicked
public void onStopClick(View view) {
mediaplayer.seekTo(0);
playbtn.setEnabled(true);
stopbtn.setEnabled(true);
}
@Override
//when the audio file is ready to play
//enable the Play button and disable the Stop button
public void onPrepared(MediaPlayer mediaplayer) {
seekbar.setMax(mediaplayer.getDuration());
changeSeekbar();
playbtn.setEnabled(true);
stopbtn.setEnabled(false);
}
private void changeSeekbar() {
seekbar.setProgress(mediaplayer.getCurrentPosition());
if (mediaplayer.isPlaying()) {
runnable = new Runnable() {
@Override
public void run() {
changeSeekbar();
}
};
handble.postDelayed(runnable, 1000);
}
};
@Override
//when the audio file plays to the end
public void onCompletion(MediaPlayer mediaplayer) {
mediaplayer.seekTo(0);
}
public void onbackClick(View view) {
i = i - 5;
mediaplayer.seekTo(i);
}
public void onskipClick(View view) {
i = i + 5;
mediaplayer.seekTo(i);
}
}
UI界面
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<ImageButton
android:id="@+id/skipBtn"
android:layout_width="83dp"
android:layout_height="85dp"
android:onClick="onskipClick"
android:scaleType="fitXY"
app:srcCompat="@drawable/skip"
tools:layout_editor_absoluteX="294dp"
tools:layout_editor_absoluteY="403dp" />
<ImageButton
android:id="@+id/stopBtn"
android:layout_width="78dp"
android:layout_height="82dp"
android:layout_marginEnd="104dp"
android:onClick="onStopClick"
android:scaleType="fitXY"
android:scaleX="1"
app:layout_constraintEnd_toEndOf="parent"
app:srcCompat="@drawable/stop"
tools:layout_editor_absoluteY="403dp" />
<ImageButton
android:id="@+id/playBtn"
android:layout_width="82dp"
android:layout_height="82dp"
android:layout_marginStart="108dp"
android:onClick="onPlayUrlClick"
android:scaleType="fitXY"
android:scaleX="1"
app:layout_constraintBottom_toBottomOf="@+id/stopBtn"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="@+id/stopBtn"
app:layout_constraintVertical_bias="0.0"
app:srcCompat="@drawable/play" />
<ImageButton
android:id="@+id/backBtn"
android:layout_width="83dp"
android:layout_height="85dp"
android:onClick="onbackClick"
android:scaleType="fitXY"
app:srcCompat="@drawable/back"
tools:layout_editor_absoluteX="16dp"
tools:layout_editor_absoluteY="400dp" />
<ImageView
android:id="@+id/imageView2"
android:layout_width="259dp"
android:layout_height="262dp"
app:srcCompat="@drawable/p"
tools:layout_editor_absoluteX="63dp"
tools:layout_editor_absoluteY="16dp" />
<SeekBar
android:id="@+id/seekBar"
android:layout_width="318dp"
android:layout_height="34dp"
tools:layout_editor_absoluteX="33dp"
tools:layout_editor_absoluteY="346dp" />
</android.support.constraint.ConstraintLayout>
uj5u.com熱心網友回復：
seekbar = (SeekBar) findViewById(R.id.seekBar);seekbar.setOnSeekBarChangeListener(...);
uj5u.com熱心網友回復：
seekbar = (SeekBar) findViewById(R.id.seekBar);在下面一點的地方,但是也在oncreate裡面,應該沒問題吧
救命啊= =明天就要交了
uj5u.com熱心網友回復：
不可以的,代碼運行是有順序的,你都不先宣告這個控制元件就設定點擊事件是找不到控制元件的
uj5u.com熱心網友回復：
我去試試,多謝你
uj5u.com熱心網友回復：
現在程式是可以運行了按鈕也能發揮作用
但是seekbar沒有跟著一起動
一動不動的站在原地
uj5u.com熱心網友回復：
自己google或者百度下mediaPlayer+seekBar播放的例子參考吧,我也沒做過uj5u.com熱心網友回復：
第43行，有空物件了，seekbar沒初始化吧轉載請註明出處，本文鏈接：https://www.uj5u.com/yidong/42417.html
標籤：Android