Trying to connect to a wifi I get ClassNotFoundException for WifiNetworkSpecifier$Builder

Question

I need to connect a smartphone to specific WiFi network that is created by other device. I'm using Xamarin.Forms to develop my app. The goal is to connect the smartphone automatically, that is, programmatically. I just need to do Android development.

This is the connection code:

public class WifiConnector : IWifiConnector
{
    public void ConnectToWifi(string ssid, string password)
    {
        try
        {
            WifiNetworkSpecifier.Builder wifiNetworkSpecifierBuilder = new WifiNetworkSpecifier.Builder();
            wifiNetworkSpecifierBuilder.SetSsid(ssid);
            wifiNetworkSpecifierBuilder.SetWpa2Passphrase(password);
            WifiNetworkSpecifier wifiNetworkSpecifier = wifiNetworkSpecifierBuilder.Build();

            NetworkRequest.Builder networkRequestBuilder = new NetworkRequest.Builder();
            networkRequestBuilder.AddTransportType(TransportType.Wifi);
            networkRequestBuilder.AddCapability(NetCapability.Internet);
            networkRequestBuilder.SetNetworkSpecifier(wifiNetworkSpecifier);
            NetworkRequest networkRequest = networkRequestBuilder.Build();

            ConnectivityManager connectivityManager = (ConnectivityManager)Android.App.Application.Context.GetSystemService(Context.ConnectivityService);
            connectivityManager.RequestNetwork(networkRequest, new NetworkCallback());
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
            Console.WriteLine(ex.StackTrace);
        }
    }

    class NetworkCallback : ConnectivityManager.NetworkCallback
    {
        public override void OnAvailable(Network network)
        {
            base.OnAvailable(network);
            Log.Debug("WifiConnector", "OnAvailable(): " + network.ToString());
        }
    }
}

I don't have any compilation errors, but at runtime I get this error:

Didn't find class "android.net.wifi.WifiNetworkSpecifier$Builder" on path: DexPathList[[zip file "/data/app/com.companyname.connecttowifi-i0OpZvWjDZqiRX01MQJcMA==/base.apk"],nativeLibraryDirectories=[/data/app/com.companyname.connecttowifi-i0OpZvWjDZqiRX01MQJcMA==/lib/arm64, /data/app/com.companyname.connecttowifi-i0OpZvWjDZqiRX01MQJcMA==/base.apk!/lib/arm64-v8a, /system/lib64, /system/vendor/lib64]]
  at Java.Interop.JniEnvironment+Types.FindClass (System.String classname) [0x0015a] in <00c315a988634383b446eff646084784>:0 
  at Java.Interop.JniType..ctor (System.String classname) [0x00006] in <00c315a988634383b446eff646084784>:0 
  at Java.Interop.JniType.GetCachedJniType (Java.Interop.JniType& cachedType, System.String classname) [0x00018] in <00c315a988634383b446eff646084784>:0 
  at Java.Interop.JniPeerMembers.get_JniPeerType () [0x0000c] in <00c315a988634383b446eff646084784>:0 
  at Java.Interop.JniPeerMembers+JniInstanceMethods.get_JniPeerType () [0x00014] in <00c315a988634383b446eff646084784>:0 
  at Java.Interop.JniPeerMembers+JniInstanceMethods.StartCreateInstance (System.String constructorSignature, System.Type declaringType, Java.Interop.JniArgumentValue* parameters) [0x0003f] in <00c315a988634383b446eff646084784>:0 
  at Android.Net.Wifi.WifiNetworkSpecifier+Builder..ctor () [0x0001f] in /Users/builder/azdo/_work/1/s/xamarin-android/src/Mono.Android/obj/Release/monoandroid10/android-30/mcw/Android.Net.Wifi.WifiNetworkSpecifier.cs:82 
  at ConnectToWifi.Droid.Services.WifiConnector.ConnectToWifi (System.String ssid, System.String password) [0x00002] in C:\DATA\Code tests\Xamarin\ConnectToWifi\ConnectToWifi\ConnectToWifi.Android\Services\WifiConnector.cs:27 
  --- End of managed Java.Lang.ClassNotFoundException stack trace ---
java.lang.ClassNotFoundException: Didn't find class "android.net.wifi.WifiNetworkSpecifier$Builder" on path: DexPathList[[zip file "/data/app/com.companyname.connecttowifi-i0OpZvWjDZqiRX01MQJcMA==/base.apk"],nativeLibraryDirectories=[/data/app/com.companyname.connecttowifi-i0OpZvWjDZqiRX01MQJcMA==/lib/arm64, /data/app/com.companyname.connecttowifi-i0OpZvWjDZqiRX01MQJcMA==/base.apk!/lib/arm64-v8a, /system/lib64, /system/vendor/lib64]]
    at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:134)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
    at crc64ee486da937c010f4.ButtonRenderer.n_onClick(Native Method)
    at crc64ee486da937c010f4.ButtonRenderer.onClick(ButtonRenderer.java:104)
    at android.view.View.performClick(View.java:7339)
    at android.widget.TextView.performClick(TextView.java:14275)
    at android.view.View.performClickInternal(View.java:7305)
    at android.view.View.access$3200(View.java:846)
    at android.view.View$PerformClick.run(View.java:27787)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7078)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:964)

I added this permissions in AndroidManifest.xml file:

<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />

Details about project, libraries and development environment:

• Microsoft Visual Studio Professional 2019 Version 16.11.12
• Xamarin.Forms 5.0.0.2012
• Android target version: Android 11 API 30
• Smartphone Android version: Android 9 API 28

Why is this error happening?

Answer 1

Hello,

I noticed this in your issue:

Android target version: Android 11 API 30

Smartphone Android version: Android 9 API 28

Referring to the Android official documentation WifiNetworkSpecifier, we can find it was added in API 29.

Therefore, you will get ClassNotFoundException for WifiNetworkSpecifier$Builder in using API 28.

If you want to implement this function in API 28, you could refer to WifiManager.

You can use if(Build.VERSION.SdkInt >= BuildVersionCodes.Q) //use WifiNetworkSpecifier; else //use WifiManager to implement this function for both API 29 below or above.

Best Regards,

Alec Liu.

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