public static final void collapseStatusBar(Context ctx) {

        Object sbservice = ctx.getSystemService("statusbar");

        try {

            Class<?> statusBarManager = Class.forName("android.app.StatusBarManager");

            Method collapse;

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {

                collapse = statusBarManager.getMethod("collapsePanels");

            } else {

                collapse = statusBarManager.getMethod("collapse");

            }

            collapse.invoke(sbservice);

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    public static final void expandStatusBar(Context ctx) {

        Object sbservice = ctx.getSystemService("statusbar");

        try {

            Class<?> statusBarManager = Class.forName("android.app.StatusBarManager");

            Method expand;

            if (Build.VERSION.SDK_INT >= ) {

                expand = statusBarManager.getMethod("expandNotificationsPanel");

            } else {

                expand = statusBarManager.getMethod("expand");

            }

            expand.invoke(sbservice);

        } catch (Exception e) {

            e.printStackTrace();

        }

    }
用途：可用于点击Notifacation之后收起状态栏

public static int getStatusBarHeight(Context context){

        Class<?> c = null;

        Object obj = null;

        Field field = null;

        int x = , statusBarHeight = ;

        try {

            c = Class.forName("com.android.internal.R$dimen");

            obj = c.newInstance();

            field = c.getField("status_bar_height");

            x = Integer.parseInt(field.get(obj).toString());

            statusBarHeight = context.getResources().getDimensionPixelSize(x);

        } catch (Exception e1) {

            e1.printStackTrace();

        }

        return statusBarHeight;

    }

 public static <T extends View> T getAdapterView(View convertView, int id) {

        SparseArray<View> viewHolder = (SparseArray<View>) convertView.getTag();

        if (viewHolder == null) {

            viewHolder = new SparseArray<View>();

            convertView.setTag(viewHolder);

        }

        View childView = viewHolder.get(id);

        if (childView == null) {

            childView = convertView.findViewById(id);

            viewHolder.put(id, childView);

        }

        return (T) childView;

    }

用法：
 @Override

    public View getView(int position, View convertView, ViewGroup parent) {

        if (convertView == null) {

            convertView = LayoutInflater.from(getActivity()).inflate(R.layout.fragment_feed_item, parent, false);

        }

        ImageView thumnailView = getAdapterView(convertView, R.id.video_thumbnail);

        ImageView avatarView =  getAdapterView(convertView, R.id.user_avatar);

        ImageView appIconView = getAdapterView(convertView, R.id.app_icon);

　　用起来非常简练，将ViewHolder隐于无形。

 <style name="TransparentActivity" parent="AppBaseTheme">

        <item name="android:windowBackground">@android:color/transparent</item>

        <item name="android:colorBackgroundCacheHint">@null</item>

        <item name="android:windowIsTranslucent">true</item>

        <item name="android:windowNoTitle">true</item>

        <item name="android:windowContentOverlay">@null</item>

    </style>

//切换到全屏

    getWindow().clearFlags(WindowManager.LayoutParams.FLAG_FORCE_NOT_FULLSCREEN);

    getActivity().getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

    //切换到非全屏

    getWindow().clearFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

    getWindow().addFlags(WindowManager.LayoutParams.FLAG_FORCE_NOT_FULLSCREEN);

注意：切换到全屏时，底部的虚拟按键仍然是显示的。次方法可多次调用用于切换

用途：播放器界面经常会用到

android.provider.Settings.System.putInt(getContentResolver(), "show_touches", );

设置1显示，设置0不显示。

 Intent intent = new Intent(Intent.ACTION_MAIN);

            intent.addCategory(Intent.CATEGORY_LAUNCHER);

            List<ResolveInfo> activities = getPackageManager().queryIntentActivities(intent, )

注意：使用getInstalledApplications会返回很多无法启动甚至没有图标的系统应用。ResolveInfo.activityInfo.applicationInfo也能取到你想要的数据。