英文:
How to pass Activity.class (this) to a method? (Android)
问题
在我的MainActivity类中，我有一个用于播放音乐的小函数：
MediaPlayer player1;if(player1 == null){player1 = MediaPlayer.create(this, R.raw.song1);player1.start();}
这很好地工作，但我想在其他活动中也使用它，所以我创建了一个MusicPlayer类：
MediaPlayer player;public void play(Context c, @RawRes int sound){if (player == null){player = MediaPlayer.create(c, sound);}player.start();}
因此，我想做的是将R.raw.song传递给play()方法。我可以通过参数@RawRes int sound传递它。
我的问题是，我如何传递this？
我在我的MainActivity类中尝试了这个：
MusicPlayer playboy;playboy.play(this, R.raw.song1);
但是我得到一个错误：
E/AndroidRuntime: FATAL EXCEPTION: mainProcess: com.example.japan, PID: 32764java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.japan/com.example.japan.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.japan.Helper.MusicPlayer.play(android.content.Context, int)' on a null object referenceat android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3333)
我还尝试了传递MainActivity.this，但是出现了相同的错误。
我做错了什么？
英文:
In my MainActivity class I have this little function to play music
MediaPlayer player1;if(player1 == null){player1 = MediaPlayer.create(this, R.raw.song1);player1.start();}
It works very fine but I want to use this for other activty too so I created a MusicPlayer class
MediaPlayer player;public void play(Context c, @RawRes int sound){if (player == null){player = MediaPlayer.create(c, sound);}player.start();}
So what I want to do is, to pass a R.raw.song to the play() method. I could pass it by the parameter @RawRes int sound
What my problem is, how can I pass this?
I tried this in my MainActivity Class
MusicPlayer playboy;playboy.play(this, R.raw.song1);
But I get an error:
E/AndroidRuntime: FATAL EXCEPTION: mainProcess: com.example.japan, PID: 32764java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.japan/com.example.japan.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.japan.Helper.MusicPlayer.play(android.content.Context, int)' on a null object referenceat android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3333)
I also tried to pass MainActivity.this but same error.
What am I doing wrong?
答案1
得分: 0
你需要首先创建你的MusicPlayer对象。在你的MainActivity类中尝试以下代码：
MusicPlayer playboy = new MusicPlayer();playboy.play(this, R.raw.song1);
英文:
You need to create your MusicPlayer object first. Try this code in your MainActivity class
MusicPlayer playboy = new MusicPlayer();playboy.play(this, R.raw.song1);
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