先上效果图，
有导航栏时

Screenshot_20210707_141532_com.matthew.demo.jpg

没有导航栏时

Screenshot_20210707_141723_com.matthew.demo.jpg

需要解决的问题

• 全屏显示
• 状态栏显示在view的上面
• 如果有标题栏需要距离顶部状态栏的高度
  -当有导航栏时需要把导航栏的高度空出来

实现

1、定义一个activity需要的theme

    <style name="MyTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <item name="android:windowTranslucentStatus">true</item>
        <item name="android:windowTranslucentNavigation">false</item>
    </style>

2、给activity设置上

        <activity android:name=".MainActivity"
            android:theme="@style/MyTheme">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

3、写一个获取状态栏高度的方法

fun getStatusBarHeight(context: Context): Int {
    //需要在Activity中执行
    var height = 0
    var resourceId = context.resources.getIdentifier("status_bar_height", "dimen", "android");
    if (resourceId > 0) {
        height = context.resources.getDimensionPixelSize(resourceId)
    }
    return height;
}

4、给标题栏设置距上的距离
我的xml时这样的

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/mn001"
    tools:context=".MainActivity">

    <LinearLayout
        android:id="@+id/ll_back"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="#ffffff"
        android:gravity="center_vertical"
        android:paddingLeft="15dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <TextView

            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Back"
            android:textSize="18dp"
            android:textStyle="bold" />
    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

给整个layout设置了一个美女做背景。然后用一个LinearLayout实现标题栏，android:id="@+id/ll_back"

在activity里设置ll_back的上边距即可

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)

        var layoutParams = ll_back.layoutParams as ConstraintLayout.LayoutParams
        layoutParams.setMargins(0, getStatusBarHeight(this), 0, 0)
    }
}

fun getStatusBarHeight(context: Context): Int {
    //需要在Activity中执行
    var height = 0
    var resourceId = context.resources.getIdentifier("status_bar_height", "dimen", "android");
    if (resourceId > 0) {
        height = context.resources.getDimensionPixelSize(resourceId)
    }
    return height;
}

bradle

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 29
    buildToolsVersion "30.0.2"

    defaultConfig {
        applicationId "com.matthew.demo"
        minSdkVersion 21
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    implementation 'androidx.core:core-ktx:1.1.0'
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

}