让Activity在Android5.0上全屏

View类提供了setSystemUiVisibility和getSystemUiVisibility方法，这两个方法实现对状态栏的动态显示或隐藏的操作，以及获取状态栏当前可见性。

setSystemUiVisibility(int visibility)方法可传入的实参为：

1. View.SYSTEM_UI_FLAG_VISIBLE：显示状态栏，Activity不全屏显示(恢复到有状态的正常情况)。

2. View.INVISIBLE：隐藏状态栏，同时Activity会伸展全屏显示。

3. View.SYSTEM_UI_FLAG_FULLSCREEN：Activity全屏显示，且状态栏被隐藏覆盖掉。

4. View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN：Activity全屏显示，但状态栏不会被隐藏覆盖，状态栏依然可见，Activity顶端布局部分会被状态遮住。

5. View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION：效果同View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN

6. View.SYSTEM_UI_LAYOUT_FLAGS：效果同View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN

7. View.SYSTEM_UI_FLAG_HIDE_NAVIGATION：隐藏虚拟按键(导航栏)。有些手机会用虚拟按键来代替物理按键。

8. View.SYSTEM_UI_FLAG_LOW_PROFILE：状态栏显示处于低能显示状态(low profile模式)，状态栏上一些图标显示会被隐藏。

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.view.View;

public class FullscreenActivity extends AppCompatActivity {

    /** * Some older devices needs a small delay between UI widget updates * and a change of the status and navigation bar. */
    private static final int UI_ANIMATION_DELAY = 300;
    private final Handler mHideHandler = new Handler();
    private View mContentView;

//在线程中使用，隐藏标题栏，状态栏和最下方的三个按钮
    private final Runnable mHidePart2Runnable = new Runnable() {
        @SuppressLint("InlinedApi")
        @Override
        public void run() {
            // Delayed removal of status and navigation bar

            // Note that some of these constants are new as of API 16 (Jelly Bean)
            // and API 19 (KitKat). It is safe to use them, as they are inlined
            // at compile-time and do nothing on earlier devices.
            mContentView.setSystemUiVisibility(
                    View.SYSTEM_UI_FLAG_LOW_PROFILE
                    | View.SYSTEM_UI_FLAG_FULLSCREEN
                    | View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                    | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
                    | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                    | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);
        }
    };
    private View mControlsView;

//显示标题栏，显示自定义的按钮
    private final Runnable mShowPart2Runnable = new Runnable() {
        @Override
        public void run() {
            // Delayed display of UI elements
            ActionBar actionBar = getSupportActionBar();
            if (actionBar != null) {
                actionBar.show();
            }
            mControlsView.setVisibility(View.VISIBLE);
        }
    };

    private boolean mVisible;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_fullscreen);

        mVisible = true;
        mControlsView = findViewById(R.id.fullscreen_content_controls);
        mContentView = findViewById(R.id.fullscreen_content);


        // Set up the user interaction to manually show or hide the system UI.
        mContentView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                toggle();
            }
        });
        toggle();
    }

    private void toggle() {
        if (mVisible) {
            hide();
        } else {
            show();
        }
    }

    private void hide() {
        // Hide UI first
        ActionBar actionBar = getSupportActionBar();
        if (actionBar != null) {
            actionBar.hide();
        }
        mControlsView.setVisibility(View.GONE);
        mVisible = false;

        // Schedule a runnable to remove the status and navigation bar after a delay
        mHideHandler.removeCallbacks(mShowPart2Runnable);
        mHideHandler.postDelayed(mHidePart2Runnable, UI_ANIMATION_DELAY);
    }

    @SuppressLint("InlinedApi")
    private void show() {
        // Show the system bar
        mContentView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION);
        mVisible = true;

        // Schedule a runnable to display UI elements after a delay
        mHideHandler.removeCallbacks(mHidePart2Runnable);
        mHideHandler.postDelayed(mShowPart2Runnable, UI_ANIMATION_DELAY);
    }
}

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:background="#0099cc" tools:context="com.my.recyclerviewdemo.FullscreenActivity">

    <!-- The primary full-screen view. This can be replaced with whatever view is needed to present your content, e.g. VideoView, SurfaceView, TextureView, etc. -->
    <TextView  android:id="@+id/fullscreen_content" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:keepScreenOn="true" android:text="@string/dummy_content" android:textColor="#33b5e5" android:textSize="50sp" android:textStyle="bold" />

    <!-- This FrameLayout insets its children based on system windows using android:fitsSystemWindows. -->
    <FrameLayout  android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true">

        <LinearLayout  android:id="@+id/fullscreen_content_controls" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_gravity="bottom|center_horizontal" android:background="@color/black_overlay" android:orientation="horizontal" tools:ignore="UselessParent">

            <Button  android:id="@+id/dummy_button" android:background="@android:color/transparent" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="@string/dummy_button" />

        </LinearLayout>
    </FrameLayout>

</FrameLayout>