當為BroadcastReceiver調用onReceive時發生NullPointerException

Question

使用我的BroadcastReceiver取回布爾值以確定是否將使用ImageButton時，我收到NullPointerException 。 我不知道為什么，我看過的所有教程都無濟於事。

這是我的代碼調用服務並調用onReceive

    //start full day timer service for natural disasters
    startService(new Intent(runGraphics.this, NaturalDisaster.class));

    //stop full day timer service for natural disasters
    stopService(new Intent(runGraphics.this, NaturalDisaster.class));

    meteorAndStormStatus = new BroadcastReceiver()
    {
        @Override
        public void onReceive(Context context, Intent intent) 
        {
            meteorExists = intent.getBooleanExtra("meteorStat", false);
            Toast.makeText(getApplicationContext(), "Here we are: " + meteorExists, Toast.LENGTH_SHORT).show();
            if (meteorExists == true)
            {
                //on click listener for meteor
                meteor = (ImageButton) findViewById(R.id.meteor);
                meteor.setVisibility(View.VISIBLE);
                meteor.setOnClickListener(new OnClickListener()
                {

                    @Override
                    public void onClick(View v) 
                    {
                        if (wasMined == false)
                        {
                            meteorRockAmount += 50;
                            wasMined = true;
                        }//end if
                    }//end onClick function

                });//end setOnClickListener
            }//end if
        }//end onReceive function
    };//end meteorAndStormStatus BroadcastReceiver
    LocalBroadcastManager.getInstance(getApplicationContext()).registerReceiver(meteorAndStormStatus, new IntentFilter("meteorStat"));

這是發送廣播的代碼

        //send broadcast back that a meteor exists
        Intent i = new Intent();
        i.putExtra("meteorStat", true);
        LocalBroadcastManager.getInstance(getApplicationContext()).sendBroadcast(i);

這是我的日志：

06-06 23:30:22.318: E/AndroidRuntime(21714): FATAL EXCEPTION: main
06-06 23:30:22.318: E/AndroidRuntime(21714): java.lang.NullPointerException
06-06 23:30:22.318: E/AndroidRuntime(21714):    at com.project.llb.runGraphics$1.onReceive(runGraphics.java:113)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at android.support.v4.content.LocalBroadcastManager.executePendingBroadcasts(LocalBroadcastManager.java:297)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at android.support.v4.content.LocalBroadcastManager.access$000(LocalBroadcastManager.java:46)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at android.support.v4.content.LocalBroadcastManager$1.handleMessage(LocalBroadcastManager.java:116)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at android.os.Handler.dispatchMessage(Handler.java:99)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at android.os.Looper.loop(Looper.java:130)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at android.app.ActivityThread.main(ActivityThread.java:3806)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at java.lang.reflect.Method.invokeNative(Native Method)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at java.lang.reflect.Method.invoke(Method.java:507)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
06-06 23:30:22.318: E/AndroidRuntime(21714):    at dalvik.system.NativeStart.main(Native Method)

另外，我確實使用onReceive在類的onPause（）中注銷了接收者。 任何幫助，將不勝感激。 提前致謝。

Answer 1

問題是我有一個if語句if（meteorExists == false），在此語句中我有meteor.setVisibility（View.INVISIBLE）。 問題是，如果不首先訪問原始的if，則會給出NullPointerException。 因此，要解決此問題，我必須添加一個流星=（ImageButton）findViewById（R.id.meteor）; 在我嘗試將流星設置為不可見之前。 感謝您的幫助。 你為我指明了正確的方向。