來自另一個類的android調用方法nullpointerexception

Question

我有一個名為HelperActivity.class ，還有另一個擴展了SherlockFragment的類。 SherlockFragment具有三種方法playAudio() ， pauseAudio() ， stopAudio();

像這樣;

public void playAudio() {

        mediaPlayer.start();

        btn_play.setEnabled(false);
        pDialog.dismiss();

        btn_pause.setEnabled(true);
        btn_stop.setEnabled(true);
    }

我想從HelperActivty.class調用此方法。 我嘗試了很多方法，但每次都遇到NullPointerException我嘗試發送上下文，並嘗試將我的方法更改為static但結果相同。請幫助。 頭等艙

public class HelperActivity extends Activity

二等

public class RadioStream extends SherlockFragment implements OnClickListener, OnTouchListener, OnCompletionListener, OnBufferingUpdateListener

錯誤;

FATAL EXCEPTION: main
01-28 02:40:50.390: E/AndroidRuntime(2915): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fedorvlasov.mostban/com.fedorvlasov.mostban.HelperActivity}: java.lang.NullPointerException
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2262)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2316)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.app.ActivityThread.access$700(ActivityThread.java:158)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1296)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.os.Looper.loop(Looper.java:176)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.app.ActivityThread.main(ActivityThread.java:5365)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at java.lang.reflect.Method.invokeNative(Native Method)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at java.lang.reflect.Method.invoke(Method.java:511)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at dalvik.system.NativeStart.main(Native Method)
01-28 02:40:50.390: E/AndroidRuntime(2915): Caused by: java.lang.NullPointerException
01-28 02:40:50.390: E/AndroidRuntime(2915):     at com.fedorvlasov.mostban.RadioStream.playAudio(RadioStream.java:310)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at com.fedorvlasov.mostban.HelperActivity.onCreate(HelperActivity.java:52)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.app.Activity.performCreate(Activity.java:5326)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)
01-28 02:40:50.390: E/AndroidRuntime(2915):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2225)
01-28 02:40:50.390: E/AndroidRuntime(2915):     ... 11 more
01-28 02:40:52.054: I/Process(2915): Sending signal. PID: 2915 SIG: 9

Answer 1

確保無論在此類中在何處調用此方法， mediaPlayer對象mediaPlayer初始化。 如果您想自己查看問題，請在代碼的第一行中放置一個斷點，然后查看該對象是否為空。