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我正在使用 eclipse 并制作一个 android 应用程序

我正在尝试保存按钮的设置，但是当我尝试在应用程序启动时设置按钮文本时，它会失败并且出现很多错误。 

    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the app.
    mSectionsPagerAdapter = new SectionsPagerAdapter(
            getSupportFragmentManager());


    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    LoadPreferences();

  .........

}private void LoadPreferences(){
        SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);
        floz = sharedPreferences.getBoolean("floz", false);

        Button button = (Button) findViewById(R.id.buttonVolumeType);
        button.setText("mls");
       }

如果我删除该button.setText("mls");行它工作正常

这是 logcat 消息

12-22 23:35:38.064: E/Trace(1384): error opening trace file: No such file or directory (2) 12-22 23:35:38.663: D/AndroidRuntime(1384): Shutting down VM 
12-22 23:35:38.663: W/dalvikvm(1384): threadid=1: thread exiting with uncaught exception (group=0x40a13300) 
12-22 23:35:38.684: E/AndroidRuntime(1384): FATAL EXCEPTION: main
12-22 23:35:38.684: E/AndroidRuntime(1384): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cheapchug/com.example.cheapchug.MainActivity}: java.lang.NullPointerException
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.os.Looper.loop(Looper.java:137)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.app.ActivityThread.main(ActivityThread.java:4745)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at java.lang.reflect.Method.invokeNative(Native Method)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at java.lang.reflect.Method.invoke(Method.java:511)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at dalvik.system.NativeStart.main(Native Method)
12-22 23:35:38.684: E/AndroidRuntime(1384): Caused by: java.lang.NullPointerException
12-22 23:35:38.684: E/AndroidRuntime(1384):     at com.example.cheapchug.MainActivity.LoadPreferences(MainActivity.java:260)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at com.example.cheapchug.MainActivity.onCreate(MainActivity.java:70)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.app.Activity.performCreate(Activity.java:5008)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
12-22 23:35:38.684: E/AndroidRuntime(1384):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
12-22 23:35:38.684: E/AndroidRuntime(1384):     ... 11 more
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1 回答 1

0

在 onCreate 方法中，该行setContentView(R.layout.main);仅加载 main.xml，因此尚未加载按钮并且无法更改按钮文本。但是onCreateOptionsMenu(Menu menu)在运行时，会加载用于滑动视图的 tab.xml 文件。

于 2013-01-22T08:19:12.710 回答