单击togglebutton时的Nullpointerexception

Question

我试图让ToggleButton工作,但我遇到了一些问题.它点击时似乎恢复到默认值,我导航到另一个屏幕.2.我尝试使用SharedPreferences将其isChecked()值转移到另一个活动,现在它崩溃了.

    <ToggleButton
    android:id="@+id/togBTN"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/homeBtn"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="106dp"
    android:text="Voice Alerts"
    android:textOff="OFF"
    android:textOn="ON" />

上面的代码在我的xml文件中.下面的代码是onClickListener代码.

         case R.id.togBTN:
         SharedPreferences.Editor editor = preferences.edit();
         editor.putBoolean("tgpref", tg.isChecked()); // value to store
         editor.commit();
     break;
     }  

这段代码是我尝试检索值的地方

SharedPreferences preferences = getPreferences(MODE_PRIVATE);
    boolean tgpref = preferences.getBoolean("tgpref", true);  //default is true
    if (tgpref = true) //if (tgpref) may be enough, not sure
    {
      speakValue = true;
    }
    else
    {
     speakValue = false;
    }

这是我得到的Logcat:

    02-21 14:49:09.587: W/dalvikvm(483): threadid=1: thread exiting with uncaught exception     (group=0x40015560)
02-21 14:49:09.597: E/AndroidRuntime(483): FATAL EXCEPTION: main
02-21 14:49:09.597: E/AndroidRuntime(483): java.lang.NullPointerException
02-21 14:49:09.597: E/AndroidRuntime(483):  at ohalleran.stephanie.Traffic.SettingsActivity.onClick(SettingsActivity.java:45)
02-21 14:49:09.597: E/AndroidRuntime(483):  at android.view.View.performClick(View.java:2485)
02-21 14:49:09.597: E/AndroidRuntime(483):  at android.widget.CompoundButton.performClick(CompoundButton.java:99)
02-21 14:49:09.597: E/AndroidRuntime(483):  at android.view.View$PerformClick.run(View.java:9080)
02-21 14:49:09.597: E/AndroidRuntime(483):  at android.os.Handler.handleCallback(Handler.java:587)
02-21 14:49:09.597: E/AndroidRuntime(483):  at android.os.Handler.dispatchMessage(Handler.java:92)
02-21 14:49:09.597: E/AndroidRuntime(483):  at android.os.Looper.loop(Looper.java:130)
02-21 14:49:09.597: E/AndroidRuntime(483):  at android.app.ActivityThread.main(ActivityThread.java:3683)
02-21 14:49:09.597: E/AndroidRuntime(483):  at java.lang.reflect.Method.invokeNative(Native Method)
02-21 14:49:09.597: E/AndroidRuntime(483):  at java.lang.reflect.Method.invoke(Method.java:507)
02-21 14:49:09.597: E/AndroidRuntime(483):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
02-21 14:49:09.597: E/AndroidRuntime(483):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
02-21 14:49:09.597: E/AndroidRuntime(483):  at dalvik.system.NativeStart.main(Native Method)

真的很感激一些帮助.

Answer 1

您应该使用== 运算符而不是=.