准备

IDE：

Android Studio 4.1.1
Build #AI-201.8743.12.41.6953283, built on November 5, 2020
Runtime version: 1.8.0_242-release-1644-b01 amd64
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 10 10.0

Android Virtual Devices：

Name: Pixel_2_API_28
CPU/ABI: Google Play Intel Atom (x86)
Path: C:\Users\86188\.android\avd\Pixel_2_API_28.avd
Target: google_apis_playstore [Google Play] (API level 28)
Skin: pixel_2
SD Card: 512M
fastboot.chosenSnapshotFile: 
runtime.network.speed: full
hw.accelerometer: yes
hw.device.name: pixel_2
hw.lcd.width: 1080
hw.initialOrientation: Portrait
image.androidVersion.api: 28
tag.id: google_apis_playstore
hw.mainKeys: no
hw.camera.front: emulated
avd.ini.displayname: Pixel 2 API 28
hw.gpu.mode: auto
hw.ramSize: 1536
PlayStore.enabled: true
fastboot.forceColdBoot: no
hw.cpu.ncore: 4
hw.keyboard: yes
hw.sensors.proximity: yes
hw.dPad: no
hw.lcd.height: 1920
vm.heapSize: 256
skin.dynamic: yes
hw.device.manufacturer: Google
hw.gps: yes
hw.audioInput: yes
image.sysdir.1: system-images\android-28\google_apis_playstore\x86\
showDeviceFrame: yes
hw.camera.back: virtualscene
AvdId: Pixel_2_API_28
hw.lcd.density: 420
hw.arc: false
hw.device.hash2: MD5:55acbc835978f326788ed66a5cd4c9a7
fastboot.forceChosenSnapshotBoot: no
fastboot.forceFastBoot: yes
hw.trackBall: no
hw.battery: yes
hw.sdCard: yes
tag.display: Google Play
runtime.network.latency: none
disk.dataPartition.size: 6442450944
hw.sensors.orientation: yes
avd.ini.encoding: UTF-8
hw.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

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

编辑 src\main\AndroidManifest.xml 清单文件，添加 ACCESS_WIFI_STATE 权限（第 7 行）：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mk">

    <!-- https://developer.android.google.cn/reference/android/Manifest.permission?hl=zh-cn#ACCESS_WIFI_STATE-->
    <!-- Allows applications to access information about Wi-Fi networks.-->
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

    ... 其他，略

</manifest>

编辑 src\main\res\layout\activity_main.xml 文件，删除原有的 TextView 元素，新增 Button 元素：

<?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"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:text="Button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

编辑 MainActivity 文件：

第 40 行：检测 WLAN 是否启用

第 52 ~ 58 行：询问用户是否前往开启 WLAN

package com.mk;

import androidx.appcompat.app.AppCompatActivity;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.wifi.WifiManager;
import android.os.Bundle;
import android.provider.Settings;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
      
      

    private Context context = this;

    private Button button = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
      
      
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initView();
    }

    private void initView() {
      
      
        button = (Button) findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {
      
      
            @Override
            public void onClick(View v) {
      
      
                // 检测 WLAN 是否启用，如果没有，提示用户前往启用
                WifiManager wifiManager = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);
                if (wifiManager == null || !wifiManager.isWifiEnabled()) {
      
       // 检测 WLAN  是否启用
                    AlertDialog.Builder builder = new AlertDialog.Builder(context);
                    AlertDialog alertDialog = builder
                            .setTitle("提示")
                            .setMessage("前往打开 WLAN？")
                            .setNegativeButton("取消", new DialogInterface.OnClickListener() {
      
      
                                @Override
                                public void onClick(DialogInterface dialog, int which) {
      
      }
                            })
                            .setPositiveButton("确定", new DialogInterface.OnClickListener() {
      
      
                                @Override
                                public void onClick(DialogInterface dialog, int which) {
      
      
                                    Intent intent = new Intent(Settings.ACTION_WIFI_SETTINGS);
                                    // https://developer.android.google.cn/guide/components/intents-filters?hl=zh-cn#ExampleSend
                                    // https://developer.android.google.cn/reference/android/content/Intent?hl=zh-cn#resolveActivity(android.content.pm.PackageManager)
                                    // 判断是否有合适的应用能够处理该 Intent，并且可以安全调用 startActivity()。
                                    if (intent.resolveActivity(getPackageManager()) != null) {
      
      
                                        startActivity(intent);
                                    }
                                }
                            })
                            .create();

                    alertDialog.show();

                    // 修改确定按钮的左边距
                    Button buttonPositive = alertDialog.getButton(AlertDialog.BUTTON_POSITIVE);
                    LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) buttonPositive.getLayoutParams();
                    layoutParams.setMargins(layoutParams.leftMargin + 20, layoutParams.topMargin, layoutParams.rightMargin, layoutParams.bottomMargin);
                    buttonPositive.setLayoutParams(layoutParams);
                } else {
      
      
                    Toast.makeText(context, "WLAN 已经启用", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

运行效果：

Android - 判断 WLAN（WiFi）是否启用

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