Android_CodeWiki_04

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。