[英]app crashes when opening
我正在嘗試制作一個在單擊按鈕時觸發聲音的應用程序。 但是每次打開應用程序時我的應用程序都會崩潰,這是java代碼的問題,因為當我刪除代碼時,它運行良好。
我的代碼是。
public class MainActivity extends Activity {
LinearLayout hello;
Button btn;
MediaPlayer sound;
@Override
protected void onPause() {
super.onPause();
sound.release();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
sound = MediaPlayer.create(this, R.raw.kick);
btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
MediaPlayer mp = MediaPlayer.create(getApplicationContext(), R.raw.kick);
mp.start();
}
});
}
}
日志貓:
java.lang.RuntimeException: Unable to start activity ComponentInfo{sp.umavibe.com.sp404/sp.umavibe.com.sp404.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2411)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2470)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1343)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5401)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:725)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:615)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at sp.umavibe.com.sp404.MainActivity.onCreate(MainActivity.java:28)
at android.app.Activity.performCreate(Activity.java:6116)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2470)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1343)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5401)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:725)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:615)
請指導我,我做錯的地方。
錯誤在於按鈕初始化
btn = (Button) findViewById(R.id.btn);
確保您在activity_main.xml
創建了一個 id 為btn
的按鈕。
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