java - 我不断收到 NullPointerException 但找不到我犯错的地方

Question

据我所知，我使用的每个变量在没有先被赋予值的情况下都不会被使用。空指针异常发生在该 Activity 开始的那一刻。抱歉，我不能更具体。

package pd.wilson.com;

import android.app.Activity;
import android.content.Intent;
 import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;

public class Page3 extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.page3);
        final RadioGroup size = (RadioGroup)findViewById(R.id.RGSize);
        final RadioGroup crust = (RadioGroup)findViewById(R.id.RGCrust);
        final RadioButton small = (RadioButton)findViewById(R.id.RBS);
        final RadioButton medium = (RadioButton)findViewById(R.id.RBM);
        final RadioButton large = (RadioButton)findViewById(R.id.RBL);
        final RadioButton regular = (RadioButton)findViewById(R.id.RBRegular);
        final RadioButton thin = (RadioButton)findViewById(R.id.RBThin);

        final String sizeS, crustS;
        if (size.getCheckedRadioButtonId() == small.getId()){
            sizeS = "Small";
            }
            else if(size.getCheckedRadioButtonId() == medium.getId()){
            sizeS = "Medium";
            }   
            else{
            sizeS = "Large";
            }
        if (crust.getCheckedRadioButtonId() == regular.getId()){
            crustS = "Regular";
            }
            else{
            crustS = "Thin";
            }

        TextView size1 = (TextView)findViewById(R.id.tvsize);
        size1.setText(sizeS);
        TextView crust1 = (TextView)findViewById(R.id.tvcrust);
        crust1.setText(crustS);


            final CheckBox sausage = (CheckBox)findViewById(R.id.cbsausage);
                int i1 = Ifchecked.gettrue(sausage);
            final CheckBox mushrooms = (CheckBox)findViewById(R.id.cbmushrooms);
                int i2 = Ifchecked.gettrue(mushrooms);
            final CheckBox pepperoni = (CheckBox)findViewById(R.id.cbpepperoni);
                int i3 = Ifchecked.gettrue(pepperoni);
            final CheckBox onions = (CheckBox)findViewById(R.id.cbonions);
                int i4 = Ifchecked.gettrue(onions);
            final CheckBox ham = (CheckBox)findViewById(R.id.cbham);
                int i5 = Ifchecked.gettrue(ham);
            final CheckBox peppers = (CheckBox)findViewById(R.id.cbpeppers);
                int i6 = Ifchecked.gettrue(peppers);
            final CheckBox beef = (CheckBox)findViewById(R.id.cbbeef);
                int i7 = Ifchecked.gettrue(beef);
            final CheckBox tomatoes = (CheckBox)findViewById(R.id.cbtomatoes);
                int i8 = Ifchecked.gettrue(tomatoes);
            final CheckBox bacon = (CheckBox)findViewById(R.id.cbbacon);
                int i9 = Ifchecked.gettrue(bacon);
            final CheckBox green = (CheckBox)findViewById(R.id.cbgreen);
                int i10 = Ifchecked.gettrue(green);
            final CheckBox olives = (CheckBox)findViewById(R.id.cbolives);
                int i11 = Ifchecked.gettrue(olives);
    int numtop = i1+i2+i3+i4+i5+i6+i7+i8+i9+i10+i11;


}
}  

堆栈跟踪:

04-04 01:41:46.536: D/AndroidRuntime(676): Shutting down VM 
04-04 01:41:46.536: W/dalvikvm(676): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
04-04 01:41:46.556: E/AndroidRuntime(676): FATAL EXCEPTION: main 
04-04 01:41:46.556: E/AndroidRuntime(676): java.lang.RuntimeException: Unable to start activity ComponentInfo{pd.wilson.com/pd.wilson.com.Page3}: java.lang.NullPointerException 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.os.Handler.dispatchMessage(Handler.java:99) 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.os.Looper.loop(Looper.java:123) 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.app.ActivityThread.main(ActivityThread.java:3683) 
04-04 01:41:46.556: E/AndroidRuntime(676): at java.lang.reflect.Method.invokeNative(Native Method) 
04-04 01:41:46.556: E/AndroidRuntime(676): at java.lang.reflect.Method.invoke(Method.java:507) 
04-04 01:41:46.556: E/AndroidRuntime(676): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
04-04 01:41:46.556: E/AndroidRuntime(676): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
04-04 01:41:46.556: E/AndroidRuntime(676): at dalvik.system.NativeStart.main(Native Method) 
04-04 01:41:46.556: E/AndroidRuntime(676): Caused by: java.lang.NullPointerException 
04-04 01:41:46.556: E/AndroidRuntime(676): at pd.wilson.com.Page3.onCreate(Page3.java:29) 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
04-04 01:41:46.556: E/AndroidRuntime(676): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
04-04 01:41:46.556: E/AndroidRuntime(676): ... 11 more 
04-04 01:41:48.256: I/Process(676): Sending signal. PID: 676 SIG: 9 
04-04 01:45:18.077: D/AndroidRuntime(733): Shutting down VM 
04-04 01:45:18.077: W/dalvikvm(733): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
04-04 01:45:18.099: E/AndroidRuntime(733): FATAL EXCEPTION: main 
04-04 01:45:18.099: E/AndroidRuntime(733): java.lang.RuntimeException: Unable to start activity ComponentInfo{pd.wilson.com/pd.wilson.com.Page3}: java.lang.NullPointerException 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.os.Handler.dispatchMessage(Handler.java:99) 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.os.Looper.loop(Looper.java:123) 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.app.ActivityThread.main(ActivityThread.java:3683) 
04-04 01:45:18.099: E/AndroidRuntime(733): at java.lang.reflect.Method.invokeNative(Native Method) 
04-04 01:45:18.099: E/AndroidRuntime(733): at java.lang.reflect.Method.invoke(Method.java:507) 
04-04 01:45:18.099: E/AndroidRuntime(733): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
04-04 01:45:18.099: E/AndroidRuntime(733): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
04-04 01:45:18.099: E/AndroidRuntime(733): at dalvik.system.NativeStart.main(Native Method) 
04-04 01:45:18.099: E/AndroidRuntime(733): Caused by: java.lang.NullPointerException 
04-04 01:45:18.099: E/AndroidRuntime(733): at pd.wilson.com.Page3.onCreate(Page3.java:29) 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
04-04 01:45:18.099: E/AndroidRuntime(733): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
04-04 01:45:18.099: E/AndroidRuntime(733): ... 11 more 
04-04 01:46:10.457: D/AndroidRuntime(767): Shutting down VM 
04-04 01:46:10.457: W/dalvikvm(767): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
04-04 01:46:10.496: E/AndroidRuntime(767): FATAL EXCEPTION: main 
04-04 01:46:10.496: E/AndroidRuntime(767): java.lang.RuntimeException: Unable to start activity ComponentInfo{pd.wilson.com/pd.wilson.com.Page3}: java.lang.NullPointerException 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.os.Handler.dispatchMessage(Handler.java:99) 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.os.Looper.loop(Looper.java:123) 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.app.ActivityThread.main(ActivityThread.java:3683) 
04-04 01:46:10.496: E/AndroidRuntime(767): at java.lang.reflect.Method.invokeNative(Native Method) 
04-04 01:46:10.496: E/AndroidRuntime(767): at java.lang.reflect.Method.invoke(Method.java:507) 
04-04 01:46:10.496: E/AndroidRuntime(767): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
04-04 01:46:10.496: E/AndroidRuntime(767): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
04-04 01:46:10.496: E/AndroidRuntime(767): at dalvik.system.NativeStart.main(Native Method) 
04-04 01:46:10.496: E/AndroidRuntime(767): Caused by: java.lang.NullPointerException 
04-04 01:46:10.496: E/AndroidRuntime(767): at pd.wilson.com.Page3.onCreate(Page3.java:29) 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
04-04 01:46:10.496: E/AndroidRuntime(767): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
04-04 01:46:10.496: E/AndroidRuntime(767): ... 11 more 
04-04 01:46:12.348: I/Process(767): Sending signal. PID: 767 SIG: 9 
04-04 01:55:31.597: D/AndroidRuntime(800): Shutting down VM 
04-04 01:55:31.597: W/dalvikvm(800): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
04-04 01:55:31.607: E/AndroidRuntime(800): FATAL EXCEPTION: main 
04-04 01:55:31.607: E/AndroidRuntime(800): java.lang.RuntimeException: Unable to start activity ComponentInfo{pd.wilson.com/pd.wilson.com.Page3}: java.lang.NullPointerException 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.os.Handler.dispatchMessage(Handler.java:99) 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.os.Looper.loop(Looper.java:123) 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.app.ActivityThread.main(ActivityThread.java:3683) 
04-04 01:55:31.607: E/AndroidRuntime(800): at java.lang.reflect.Method.invokeNative(Native Method) 
04-04 01:55:31.607: E/AndroidRuntime(800): at java.lang.reflect.Method.invoke(Method.java:507) 
04-04 01:55:31.607: E/AndroidRuntime(800): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
04-04 01:55:31.607: E/AndroidRuntime(800): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
04-04 01:55:31.607: E/AndroidRuntime(800): at dalvik.system.NativeStart.main(Native Method) 
04-04 01:55:31.607: E/AndroidRuntime(800): Caused by: java.lang.NullPointerException 
04-04 01:55:31.607: E/AndroidRuntime(800): at pd.wilson.com.Page3.onCreate(Page3.java:29) 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
04-04 01:55:31.607: E/AndroidRuntime(800): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
04-04 01:55:31.607: E/AndroidRuntime(800): ... 11 more 
04-04 01:55:33.357: I/Process(800): Sending signal. PID: 800 SIG: 9 

Answer 1

基于您的堆栈跟踪:

04-04 01:41:46.556: E/AndroidRuntime(676): Caused by: java.lang.NullPointerException 
04-04 01:41:46.556: E/AndroidRuntime(676): at pd.wilson.com.Page3.onCreate(Page3.java:29) 

看起来该文件的第 29 行就是问题所在:

if (size.getCheckedRadioButtonId() == small.getId()){

size 或 small 可能是空引用，因此您应该检查一下。

如果结果其中之一为 null(可能)，Google for android findviewbyid return null 会发现相当多的潜在原因。