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 >= 17) {                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 = 0, statusBarHeight = 0;        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", 1);

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, 0)

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。