java我的应用程序因NullPointerException崩溃。为什么？

3 周，5 日 Questions & Answers 382

我有一个叫做信息的菜单按钮，当我触摸它时，我想启动一个叫做“InformationActivity”的新活动。我已经验证了代码，但似乎什么都没用。我得到一个空指针异常和一个致命异常：Main。为什么会这样？查看代码以查看失败的地方。谢谢

以下是与菜单相关的所有内容

@Override
    public boolean onCreateOptionsMenu(Menu menu){

        menu.add(1,INFORMATION,1,"Information");
        Log.w("I AM HERE ?!", "YES01");
        return true;

        }
    public boolean onOptionsItemSelected (MenuItem item){
        switch (item.getItemId()){
        case INFORMATION:
            Log.w("I AM HERE ?!", "YES02");
            Toast.makeText(getApplicationContext(), "This works - tested.", Toast.LENGTH_LONG).show();
            Intent infoIntent = new Intent(this,InformationActivity.class);
            Log.w("I AM HERE ?!", infoIntent.toString());

//此日志显示为“package name/.InformationActivity”-为什么？！这是正确的格式吗？星触觉（infoIntent）//这里失败了。返回true

        default:
            return super.onOptionsItemSelected(item);

        }

以下是AndroidManifest中的相关代码。xml

<activity
            安卓:name="com.example.pingtest.InformationActivity"
            安卓:label="@string/title_activity_information" >
        </activity>

以下是活动信息。xml文件。注意，我在InformationActivity类的Java代码中使用了线性布局。然而，它并没有出现在这里。我不需要它，因为我使用Java在那里添加了一个新的文本视图。希望这是有道理的

<RelativeLayout xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
    xmlns:tools="http://schemas.安卓.com/tools"
    安卓:layout_width="match_parent"
    安卓:layout_height="match_parent"
    安卓:paddingBottom="@dimen/activity_vertical_margin"
    安卓:paddingLeft="@dimen/activity_horizontal_margin"
    安卓:paddingRight="@dimen/activity_horizontal_margin"
    安卓:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".InformationActivity" >

    <TextView
        安卓:layout_width="wrap_content"
        安卓:layout_height="wrap_content"
        />

</RelativeLayout>

这是Logcat的输出

11-29 16:55:04.223: I/ViewRootImpl(2740): ViewRoot's KeyEvent { action=ACTION_DOWN, keyCode=KEYCODE_MENU, scanCode=139, metaState=0, flags=0x48, repeatCount=0, eventTime=60889321, downTime=60889321, deviceId=7, source=0x101 } to com.安卓.internal.policy.impl.PhoneWindow$DecorView{4286a2b8 V.E..... R....... 0,0-1080,1920}
11-29 16:55:04.293: I/ViewRootImpl(2740): ViewRoot's KeyEvent { action=ACTION_UP, keyCode=KEYCODE_MENU, scanCode=139, metaState=0, flags=0x48, repeatCount=0, eventTime=60889391, downTime=60889321, deviceId=7, source=0x101 } to com.安卓.internal.policy.impl.PhoneWindow$DecorView{4286a2b8 V.E..... R....... 0,0-1080,1920}
11-29 16:55:04.873: I/ViewRootImpl(2740): ViewRoot's Touch Event : Touch Down
11-29 16:55:04.933: I/ViewRootImpl(2740): ViewRoot's Touch Event : Touch UP
11-29 16:55:05.003: W/I AM HERE ?!(2740): YES02
11-29 16:55:05.023: W/I AM HERE ?!(2740): Intent { cmp=com.example.pingtest/.InformationActivity }
11-29 16:55:05.023: I/ActivityManager(2740): Timeline: Activity_launch_request id:com.example.pingtest time:60890123
11-29 16:55:05.093: D/AndroidRuntime(2740): Shutting down VM
11-29 16:55:05.093: W/dalvikvm(2740): threadid=1: thread exiting with uncaught exception (group=0x41822e48)
11-29 16:55:05.103: E/AndroidRuntime(2740): FATAL EXCEPTION: main
11-29 16:55:05.103: E/AndroidRuntime(2740): Process: com.example.pingtest, PID: 2740
11-29 16:55:05.103: E/AndroidRuntime(2740): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.pingtest/com.example.pingtest.InformationActivity}: java.lang.NullPointerException
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2202)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2252)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.app.ActivityThread.access$800(ActivityThread.java:139)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1200)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.os.Handler.dispatchMessage(Handler.java:102)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.os.Looper.loop(Looper.java:136)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.app.ActivityThread.main(ActivityThread.java:5103)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at java.lang.reflect.Method.invokeNative(Native Method)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at java.lang.reflect.Method.invoke(Method.java:515)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:606)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at dalvik.system.NativeStart.main(Native Method)
11-29 16:55:05.103: E/AndroidRuntime(2740): Caused by: java.lang.NullPointerException
11-29 16:55:05.103: E/AndroidRuntime(2740):     at com.example.pingtest.InformationActivity.onCreate(InformationActivity.java:24)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.app.Activity.performCreate(Activity.java:5275)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-29 16:55:05.103: E/AndroidRuntime(2740):     at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2166)
11-29 16:55:05.103: E/AndroidRuntime(2740):     ... 11 more

这是信息活动。java文件。我没有看到任何错误

public class InformationActivity extends Activity {
    LinearLayout layout2;
    TextView label2;
    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        //readTask = new ReadTask();
        Typeface type = Typeface.createFromAsset(getAssets(),"fonts/41370_WINDSORCONDENSED.TTF");
        layout2=new LinearLayout(this);
        label2.setText("Text here\n");
        label2.setTextColor(Color.rgb(0,0,0));
        label2.setBackgroundColor(Color.rgb(255,194,75));
        label2.setTypeface(type);
        setContentView(R.layout.activity_information);
    }

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java我的应用程序因NullPointerException崩溃。为什么？

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