java - 当指定仅使用 wifi 时，ConnectivityManager Network 为 null

Question

我正在尝试通过 ConnectivityManager 存储 wifi 网络(最终是蜂窝网络)，以便稍后在我的程序中使用，以同时通过本地 Wifi 或蜂窝网络发送数据。我已经按照这篇文章( Make Android simultaneously use WiFi to talk to a device and mobile data to talk to a server? 和 How to stay connected through mobile network after WIFI is connected on Android? )尝试让它运行。然而，mWifiNetwork 为空。使用 Debug模式，变量 mWifiNetwork 显示为 "108"，然后当 '''onAvailable''' 方法完成时，变量返回为 null。不确定为什么变量没有正确存储网络。

我创建了一个在 onResume 中调用的 ForceWifiNetwork 类

forceWifiNetwork.java

public class forceWifiNetwork {

    //setting up a context variable and method to use "getSystemService"
    // this way we do not need to extend MainActivity class to this class
    // But when we initialize this class in main activity we will have to pass in "this" to the class as a parameter

    Context mContext;
    private ConnectivityManager.NetworkCallback mWifiNetworkCallback;
    public Network mWifiNetwork;
    final ConnectivityManager manager;



    public forceWifiNetwork(Context mContext){
        this.mContext = mContext;
        manager = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
    }




    public void cellConnect(){

        if (mWifiNetworkCallback == null){

            // Init only once
            mWifiNetworkCallback = new ConnectivityManager.NetworkCallback(){
                @Override
                public void onAvailable(final Network network){
                    try{
                        //Save this network for later use
                        mWifiNetwork = network;
                    }catch(Exception e){
                        Log.i("onAvailable ERROR","Error in onAvailable method");
                    }
                }
            };
        }

        NetworkRequest.Builder wifiBuilder;
        wifiBuilder = new NetworkRequest.Builder();
        //set the transport type to do wifi
        wifiBuilder.addTransportType(NetworkCapabilities.TRANSPORT_WIFI);
        //wifiBuilder.addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET);
        manager.requestNetwork(wifiBuilder.build(),mWifiNetworkCallback);


    }

}

onResume(在 MainActivity.java 中)

    @Override
    public void onResume(){
        super.onResume();

        try {
            forceWifiNetwork myWifiNetwork = new forceWifiNetwork(this);
            myWifiNetwork.cellConnect();
            if (myWifiNetwork.mWifiNetwork == null) {
                Log.i("onResume", "mWifiNetwork is null");
            } else {
                Log.i("onResume", "mWifiNetwork is not null");
            }
        }catch(Exception e){
            Log.i("ERROR IN ONRESUME","error");
            e.printStackTrace();
        }


    }

我目前在 AndroidManifest.xml 中也拥有这些权限

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

Answer 1

将forceWifiNetwork的启动移至onCreate而不是onResume中。我相信 ConnectivityManager.Networkcallback 中的 onAvailable 方法可能具有一些底层异步属性。它看起来像这样。

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

        //creating network variables that store wifi and cell networks
        myWifiNetwork = new forceWifiNetwork(this);


        try {
            myWifiNetwork.cellConnect();
            if (myWifiNetwork.mWifiNetwork == null) {
                Log.i("onCreate", "mWifiNetwork is null");
            } else {
                Log.i("onCreate", "mWifiNetwork is not null");
            }
        }catch(Exception e){
            Log.i("Error in onCreate","error creating network");
            e.printStackTrace();
        }


    }