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Hide the navigation bar

This lesson describes how to hide the navigation bar, which was introduced in Android 4.0 (API level 14).

Even though this lesson focuses on hiding the navigation bar, you should design your app to hide the status bar at the same time, as described in . Hiding the navigation and status bars (while still keeping them readily accessible) lets the content use the entire display space, thereby providing a more immersive user experience.

Figure 1. Navigation bar.

Hide the Navigation Bar

You can hide the navigation bar using the SYSTEM_UI_FLAG_HIDE_NAVIGATION flag. This snippet hides both the navigation bar and the status bar:

View decorView = getWindow().getDecorView();// Hide both the navigation bar and the status bar.// SYSTEM_UI_FLAG_FULLSCREEN is only available on Android 4.1 and higher, but as// a general rule, you should design your app to hide the status bar whenever you// hide the navigation bar.int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION              | View.SYSTEM_UI_FLAG_FULLSCREEN;decorView.setSystemUiVisibility(uiOptions);

Note the following:

• With this approach, touching anywhere on the screen causes the navigation bar (and status bar) to reappear and remain visible. The user interaction causes the flags to be be cleared.
• Once the flags have been cleared, your app needs to reset them if you want to hide the bars again. See for a discussion of how to listen for UI visibility changes so that your app can respond accordingly.
• Where you set the UI flags makes a difference. If you hide the system bars in your activity’s onCreate() method and the user presses Home, the system bars will reappear. When the user reopens the activity, onCreate() won’t get called, so the system bars will remain visible. If you want system UI changes to persist as the user navigates in and out of your activity, set UI flags in onResume() or onWindowFocusChanged().
• The method setSystemUiVisibility() only has an effect if the view you call it from is visible.
• Navigating away from the view causes flags set with setSystemUiVisibility() to be cleared.

Make Content Appear Behind the Navigation Bar

On Android 4.1 and higher, you can set your application’s content to appear behind the navigation bar, so that the content doesn’t resize as the navigation bar hides and shows. To do this, use SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION. You may also need to use SYSTEM_UI_FLAG_LAYOUT_STABLE to help your app maintain a stable layout.

When you use this approach, it becomes your responsibility to ensure that critical parts of your app’s UI don’t end up getting covered by system bars. For more discussion of this topic, see the lesson.

准备

IDE：

Android Studio 4.1.1Build #AI-201.8743.12.41.6953283, built on November 5, 2020Runtime version: 1.8.0_242-release-1644-b01 amd64VM: OpenJDK 64-Bit Server VM by JetBrains s.r.oWindows 10 10.0

Android Virtual Devices：

Name: Pixel_2_API_28CPU/ABI: Google Play Intel Atom (x86)Path: C:\Users\86188\.android\avd\Pixel_2_API_28.avdTarget: google_apis_playstore [Google Play] (API level 28)Skin: pixel_2SD Card: 512Mfastboot.chosenSnapshotFile: runtime.network.speed: fullhw.accelerometer: yeshw.device.name: pixel_2hw.lcd.width: 1080hw.initialOrientation: Portraitimage.androidVersion.api: 28tag.id: google_apis_playstorehw.mainKeys: nohw.camera.front: emulatedavd.ini.displayname: Pixel 2 API 28hw.gpu.mode: autohw.ramSize: 1536PlayStore.enabled: truefastboot.forceColdBoot: nohw.cpu.ncore: 4hw.keyboard: yeshw.sensors.proximity: yeshw.dPad: nohw.lcd.height: 1920vm.heapSize: 256skin.dynamic: yeshw.device.manufacturer: Googlehw.gps: yeshw.audioInput: yesimage.sysdir.1: system-images\android-28\google_apis_playstore\x86\showDeviceFrame: yeshw.camera.back: virtualsceneAvdId: Pixel_2_API_28hw.lcd.density: 420hw.arc: falsehw.device.hash2: MD5:55acbc835978f326788ed66a5cd4c9a7fastboot.forceChosenSnapshotBoot: nofastboot.forceFastBoot: yeshw.trackBall: nohw.battery: yeshw.sdCard: yestag.display: Google Playruntime.network.latency: nonedisk.dataPartition.size: 6442450944hw.sensors.orientation: yesavd.ini.encoding: UTF-8hw.gpu.enabled: yes

注意：以下示例仅在安卓虚拟设备上运行测试，并没有在真实的设备上运行测试。

项目

效果：

新建项目，选择 Empty Activity，在配置项目时，Minimum SDK 选择 API 16: Android 4.1 (Jelly Bean)

编辑 src\main\res\layout\activity_main.xml 布局文件，添加 Toolbar 和 Button 组件：

编辑 MainActivity 文件：

1. 初始化 Toolbar（第 18 ~ 19 行）；

2. 为按钮绑定点击事件，当用户点击按钮之后，将 MainActivity 置于 Statu Bar 和 Navigation Bar 之后（第 21 ~ 35 行）；

3. 重写 onResume() 方法，添加隐藏 Status Bar 和 Navigation Bar 代码（第 38 ~ 52 行）。

   注意：当用户点击屏幕任意一处，Status Bar 和 Navigation Bar 都将重现。

package com.mk;import androidx.appcompat.app.AppCompatActivity;import androidx.appcompat.widget.Toolbar;import android.os.Build;import android.os.Bundle;import android.view.View;import android.widget.Button;public class MainActivity extends AppCompatActivity {       @Override    protected void onCreate(Bundle savedInstanceState) {           super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);        setSupportActionBar(toolbar);        Button button = (Button) findViewById(R.id.button);        button.setOnClickListener(new View.OnClickListener() {               @Override            public void onClick(View v) {                   // On Android 4.1 and higher, you can set your application's content                // to appear behind the navigation bar, so that the content                // doesn't resize as the navigation bar hides and shows.                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {                       View decorView = getWindow().getDecorView();                    int uiOptions = View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION                            | View.SYSTEM_UI_FLAG_LAYOUT_STABLE;                    decorView.setSystemUiVisibility(uiOptions);                }            }        });    }    @Override    protected void onResume() {           super.onResume();        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {               View decorView = getWindow().getDecorView();            // Hide both the navigation bar and the status bar.            // SYSTEM_UI_FLAG_FULLSCREEN is only available on Android 4.1 and higher, but as            // a general rule, you should design your app to hide the status bar whenever you            // hide the navigation bar.            int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION                    | View.SYSTEM_UI_FLAG_FULLSCREEN;            decorView.setSystemUiVisibility(uiOptions);        }    }}

参考