安卓布局中的javanpe

Question

我开发了一些安卓程序，但它在安卓4.4.2上抛出NLE，在安卓4.1.2上运行良好

我认为问题在于：setContentView（R.layout.drawerlayout）； 但是我的抽屉布局没有错误

部分代码：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //setContentView(R.layout.activity_main);
    setContentView(R.layout.drawerlayout);

    if (安卓.os.Build.VERSION.SDK_INT > 9) {
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
                .permitAll().build();
        StrictMode.setThreadPolicy(policy);
    }

  SharedPreferences pref = getApplicationContext().getSharedPreferences("setting", 0); // 0 - for private mode


      login=pref.getBoolean("loged_in", false);


    Drawable d=getResources().getDrawable(R.drawable.action_bar_bg);  
    getActionBar().setBackgroundDrawable(d);


    try {
        catnum = 1;
        addcat("دسته بندی ها",0);
        new CateFetch().execute("a","c", "b");
        mTitle = mDrawerTitle = getTitle();
        mPlanetTitles = arr;// getResources().getStringArray(R.array.planets_array);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.left_drawer);

    } catch (Exception E) {
    }


    // set a custom shadow that overlays the main content when the drawer opens
    mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);
    // set up the drawer's list view with items and click listener
    mDrawerList.setAdapter(new ArrayAdapter<String>(this,
            R.layout.drawer_list_item, mPlanetTitles));
    mDrawerList.setOnItemClickListener(new DrawerItemClickListener());

    // enable ActionBar app icon to behave as action to toggle nav drawer
    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setHomeButtonEnabled(true);

    // ActionBarDrawerToggle ties together the the proper interactions
    // between the sliding drawer and the action bar app icon
    mDrawerToggle = new ActionBarDrawerToggle(
            this,                  /* host Activity */
            mDrawerLayout,         /* DrawerLayout object */
            R.drawable.ic_drawer,  /* nav drawer image to replace 'Up' caret */
            R.string.drawer_open,  /* "open drawer" description for accessibility */
            R.string.drawer_close  /* "close drawer" description for accessibility */
            ) {
        public void onDrawerClosed(View view) {
            getActionBar().setTitle(mTitle);
            invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
        }

        public void onDrawerOpened(View drawerView) {
            getActionBar().setTitle(mDrawerTitle);
            invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    if (savedInstanceState == null) {
        selectItem(0);
    }
}

日志：

07-26 09:14:07.519    2167-2167/com.example.安卓.navigationdrawerexample D/dalvikvm﹕ GC_FOR_ALLOC freed 91K, 6% free 2900K/3068K, paused 33ms, total 36ms
07-26 09:14:07.859    2167-2167/com.example.安卓.navigationdrawerexample D/AndroidRuntime﹕ Shutting down VM
07-26 09:14:07.859    2167-2167/com.example.安卓.navigationdrawerexample W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xb2aa3ba8)
07-26 09:14:07.919    2167-2167/com.example.安卓.navigationdrawerexample D/dalvikvm﹕ GC_FOR_ALLOC freed 28K, 3% free 3383K/3488K, paused 22ms, total 23ms
07-26 09:14:07.929    2167-2167/com.example.安卓.navigationdrawerexample E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.安卓.navigationdrawerexample, PID: 2167
    java.lang.NullPointerException
            at 安卓.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)
            at 安卓.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
            at 安卓.widget.AbsListView.obtainView(AbsListView.java:2263)
            at 安卓.widget.ListView.makeAndAddView(ListView.java:1790)
            at 安卓.widget.ListView.fillDown(ListView.java:691)
            at 安卓.widget.ListView.fillFromTop(ListView.java:752)
            at 安卓.widget.ListView.layoutChildren(ListView.java:1630)
            at 安卓.widget.AbsListView.onLayout(AbsListView.java:2091)
            at 安卓.view.View.layout(View.java:14817)
            at 安卓.view.ViewGroup.layout(ViewGroup.java:4631)
            at 安卓.support.v4.widget.DrawerLayout.onLayout(DrawerLayout.java:672)
            at 安卓.view.View.layout(View.java:14817)
            at 安卓.view.ViewGroup.layout(ViewGroup.java:4631)
            at 安卓.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
            at 安卓.widget.FrameLayout.onLayout(FrameLayout.java:388)
            at 安卓.view.View.layout(View.java:14817)
            at 安卓.view.ViewGroup.layout(ViewGroup.java:4631)
            at com.安卓.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:374)
            at 安卓.view.View.layout(View.java:14817)
            at 安卓.view.ViewGroup.layout(ViewGroup.java:4631)
            at 安卓.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
            at 安卓.widget.FrameLayout.onLayout(FrameLayout.java:388)
            at 安卓.view.View.layout(View.java:14817)
            at 安卓.view.ViewGroup.layout(ViewGroup.java:4631)
            at 安卓.view.ViewRootImpl.performLayout(ViewRootImpl.java:1987)
            at 安卓.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1744)
            at 安卓.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
            at 安卓.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
            at 安卓.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
            at 安卓.view.Choreographer.doCallbacks(Choreographer.java:574)
            at 安卓.view.Choreographer.doFrame(Choreographer.java:544)
            at 安卓.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
            at 安卓.os.Handler.handleCallback(Handler.java:733)
            at 安卓.os.Handler.dispatchMessage(Handler.java:95)
            at 安卓.os.Looper.loop(Looper.java:136)
            at 安卓.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

如何解决

Answer 1

它与setContentView(R.layout.drawerlayout);无关

arr必须在mPlanetTitles = arr;// getResources().getStringArray(R.array.planets_array);之前有元素

在onCreate的早期添加一个arr= new String[]{"some string"};

或者更改数组的填充位置

Answer 2

当ListView尝试添加其子视图时，必须确保ArrayAdapter中的所有元素都是非null。否则会导致NPE。使用AsyncTask填充元素在没有一些更改的情况下是行不通的，因为它不能保证在ListView添加子元素之前填充数组

如果要从AsyncTask填充ArrayAdapter，可以使用List（我建议ArrayList）作为构造函数参数创建ArrayAdapter，替换数组或删除数组作为参数，使ArrayAdapter创建自己的列表。使用在UI线程上运行的AsyncTask方法中的^{}，例如^{}，来填充ArrayAdapter