安卓8+-如何在安卓系统中编程连接wifi网络？

Question

使用Android 8+使用Android Studio 3.6.3和api target 29工作，下面的代码反映了使用设置用户添加的wifi配置，建立两个设备之间的连接，并保持它的活力，直到用户断开任何一个设备，下面的代码试图获得数据输入，并试图连接到给定的配置，但在运行应用程序时，我得到了java.lang.NoClassDefFoundError。

import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.net.MacAddress;
import android.net.wifi.WifiManager;
import android.net.wifi.WifiNetworkSuggestion;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Button;

import java.util.Collections;

public class MainActivity extends AppCompatActivity {
    EditText etssid, etpass;
    Button btconnect;
    String id, pass;
    Context context = this;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        etssid = findViewById(R.id.etssid);
        etpass = findViewById(R.id.etpass);
        btconnect = findViewById(R.id.btnconnect);

        btconnect.setOnClickListener(new View.OnClickListener() {
            @RequiresApi(api = Build.VERSION_CODES.P)
            @Override
            public void onClick(View v) {
                id = etssid.getText().toString();
                pass = etpass.getText().toString();
                final WifiNetworkSuggestion conf = new WifiNetworkSuggestion.Builder()
                        .setBssid(MacAddress.fromString(id))
                        .setWpa2Passphrase(pass)
                        .setIsAppInteractionRequired(false)
                        .build();
                final WifiManager wifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
                final int status = wifiManager.addNetworkSuggestions(Collections.singletonList(conf));
                if(status != WifiManager.STATUS_NETWORK_SUGGESTIONS_SUCCESS)
                {
                    //error handling
                }
            }
        });
    }
}

当按下连接按钮时，在deb时显示以下错误

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.client, PID: 6553
    java.lang.NoClassDefFoundError: Failed resolution of: Landroid/net/wifi/WifiNetworkSuggestion$Builder;
        at com.example.client.MainActivity$1.onClick(MainActivity.java:38)
        at android.view.View.performClick(View.java:6294)
        at android.view.View$PerformClick.run(View.java:24774)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6518)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
     Caused by: java.lang.ClassNotFoundException: Didn't find class "android.net.wifi.WifiNetworkSuggestion$Builder" on path: DexPathList[[zip file "/data/app/com.example.client-YUhhKlGEU_94ZLx0o-xLOA==/base.apk"],nativeLibraryDirectories=[/data/app/com.example.client-YUhhKlGEU_94ZLx0o-xLOA==/lib/arm64, /system/lib64, /system/vendor/lib64]]
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:125)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
        at com.example.client.MainActivity$1.onClick(MainActivity.java:38) 
        at android.view.View.performClick(View.java:6294) 
        at android.view.View$PerformClick.run(View.java:24774) 
        at android.os.Handler.handleCallback(Handler.java:790) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6518) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)ugging,

Answer 1

因为这个API是在SDK 29中添加的，在这里可以看到。

https:/developer.android.comreferenceandroidnetwifiWifiNetworkSuggestion。

它在< 29上根本不存在。如果你把SDK降低到目标28，它也不会在类中找到你的导入。