目录

• 概述
• 问题分析
• 总结

概述

在最近开发过程中需要获取当前wifi的SSID，目前网上一般推荐 mWifiManager.getConnectionInfo() 这个方法来进行获取，但是发现在Android12上这个方法已经被标记为过时，本着用最新方法的想法，决定使用推荐的新方法试试。

问题分析

一言不合看源码，既然该方法被标记为过时，那么应该也会有推荐的方法来使用，源码如下：

 /**
    //path:packages/modules/Wifi/framework/java/android/net/wifi/WifiManager.java
     * Return dynamic information about the current Wi-Fi connection, if any is active.
     * <p>
     *
     * @return the Wi-Fi information, contained in {@link WifiInfo}.
     *
     * @deprecated Starting with {@link Build.VERSION_CODES#S}, WifiInfo retrieval is moved to
     * {@link ConnectivityManager} API surface. WifiInfo is attached in
     * {@link NetworkCapabilities#getTransportInfo()} which is available via callback in
     * {@link NetworkCallback#onCapabilitiesChanged(Network, NetworkCapabilities)} or on-demand from
     * {@link ConnectivityManager#getNetworkCapabilities(Network)}.
     *
     *</p>
     * Usage example:
     * <pre>{@code
     * final NetworkRequest request =
     *      new NetworkRequest.Builder()
     *      .addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
     *      .build();
     * final ConnectivityManager connectivityManager =
     *      context.getSystemService(ConnectivityManager.class);
     * final NetworkCallback networkCallback = new NetworkCallback() {
     *      ...
     *      {@literal @}Override
     *      void onAvailable(Network network) {}
     *
     *      {@literal @}Override
     *      void onCapabilitiesChanged(Network network, NetworkCapabilities networkCapabilities) {
     *          WifiInfo wifiInfo = (WifiInfo) networkCapabilities.getTransportInfo();
     *      }
     *      // etc.
     * };
     * connectivityManager.requestNetwork(request, networkCallback); // For request
     * connectivityManager.registerNetworkCallback(request, networkCallback); // For listen
     * }</pre>
     * <p>
     * <b>Compatibility Notes:</b>
     * <li>Apps can continue using this API, however newer features
     * such as ability to mask out location sensitive data in WifiInfo will not be supported
     * via this API. </li>
     * <li>On devices supporting concurrent connections (indicated via
     * {@link #isStaConcurrencyForLocalOnlyConnectionsSupported()}, etc) this API will return
     * the details of the internet providing connection (if any) to all apps, except for the apps
     * that triggered the creation of the concurrent connection. For such apps, this API will return
     * the details of the connection they created. e.g. apps using {@link WifiNetworkSpecifier} will
     * trigger a concurrent connection on supported devices and hence this API will provide
     * details of their peer to peer connection (not the internet providing connection). This
     * is to maintain backwards compatibility with behavior on single STA devices.</li>
     * </p>
     */
    @Deprecated
    public WifiInfo getConnectionInfo() {
        try {
            return mService.getConnectionInfo(mContext.getOpPackageName(),
                    mContext.getAttributionTag());
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

根据注释里的提示，谷歌推荐使用NetworkCallback监听网络状态的方法来获取wifi 的ssid，照着写一下，如下：

 final NetworkRequest request =
           new NetworkRequest.Builder()
           .addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
           .build();

 final ConnectivityManager.NetworkCallback mNetworkCallback = new ConnectivityManager.NetworkCallback() {
        @Override
        public void onAvailable(@NonNull Network network) {
            super.onAvailable(network);
        }

        @Override
        public void onCapabilitiesChanged(@NonNull Network network, @NonNull NetworkCapabilities networkCapabilities) {
            super.onCapabilitiesChanged(network, networkCapabilities);
            WifiInfo wifiInfo = (WifiInfo) networkCapabilities.getTransportInfo();
            if (wifiInfo != null) {
            String ssid = wifiInfo.getSSID().replace("\"", "").replace("<", "").replace(">", ""));
            } 
        }
    };

	private void requestNetwork() {
        mConnectivityManager.registerNetworkCallback(mRequest, mNetworkCallback);
    }
    
	 private void unrequestNetwork() {
        mConnectivityManager.unregisterNetworkCallback(mNetworkCallback);
    }

本以为万事大吉，一切OK，没想到install以后拿到的ssid 一直是 unknow ssid。对于这种情况，第一想法是应用是否缺少权限？查看WifiInfo源码，发现在应用没有"Manifest.permission.ACCESS_FINE_LOCATION"权限时，ssid的确会返回Unknown Ssid。难道这就解决了？看了一下应用的清单文件，发现该有的权限配置都是有的。这~ 给我整不会了！
纠结了好几天，始终没有找到解决问题的办法。
偶然在查看NetworkCallback源码的时候好像发现了新大陆。

//path:packages/modules/Connectivity/framework/src/android/net/ConnectivityManager.java
    /**
     * Base class for {@code NetworkRequest} callbacks. Used for notifications about network
     * changes. Should be extended by applications wanting notifications.
     *
     * A {@code NetworkCallback} is registered by calling
     * {@link #requestNetwork(NetworkRequest, NetworkCallback)},
     * {@link #registerNetworkCallback(NetworkRequest, NetworkCallback)},
     * or {@link #registerDefaultNetworkCallback(NetworkCallback)}. A {@code NetworkCallback} is
     * unregistered by calling {@link #unregisterNetworkCallback(NetworkCallback)}.
     * A {@code NetworkCallback} should be registered at most once at any time.
     * A {@code NetworkCallback} that has been unregistered can be registered again.
     */
    public static class NetworkCallback {
        /**
         * No flags associated with this callback.
         * @hide
         */
        public static final int FLAG_NONE = 0;
        /**
         * Use this flag to include any location sensitive data in {@link NetworkCapabilities} sent
         * via {@link #onCapabilitiesChanged(Network, NetworkCapabilities)}.
         * <p>
         * These include:
         * <li> Some transport info instances (retrieved via
         * {@link NetworkCapabilities#getTransportInfo()}) like {@link android.net.wifi.WifiInfo}
         * contain location sensitive information.
         * <li> OwnerUid (retrieved via {@link NetworkCapabilities#getOwnerUid()} is location
         * sensitive for wifi suggestor apps (i.e using {@link WifiNetworkSuggestion}).</li>
         * </p>
         * <p>
         * Note:
         * <li> Retrieving this location sensitive information (subject to app's location
         * permissions) will be noted by system. </li>
         * <li> Without this flag any {@link NetworkCapabilities} provided via the callback does
         * not include location sensitive info.
         * </p>
         */
        // Note: Some existing fields which are location sensitive may still be included without
        // this flag if the app targets SDK < S (to maintain backwards compatibility).
        public static final int FLAG_INCLUDE_LOCATION_INFO = 1 << 0;

        /** @hide */
        @Retention(RetentionPolicy.SOURCE)
        @IntDef(flag = true, prefix = "FLAG_", value = {
                FLAG_NONE,
                FLAG_INCLUDE_LOCATION_INFO
        })
        public @interface Flag { }

        /**
         * All the valid flags for error checking.
         */
        private static final int VALID_FLAGS = FLAG_INCLUDE_LOCATION_INFO;

        public NetworkCallback() {
            this(FLAG_NONE);
        }

        public NetworkCallback(@Flag int flags) {
            if ((flags & VALID_FLAGS) != flags) {
                throw new IllegalArgumentException("Invalid flags");
            }
            mFlags = flags;
        }
        ...

发现NetworkCallback的构造方法中是可以传参数的，并且根据注释可知 FLAG_INCLUDE_LOCATION_INFO 这个flag就是控制onCapabilitiesChanged时 NetworkCapabilities#getTransportInfo() 可以传递一些敏感的位置信息，而获取WifiInfo中的ssid的确需要位置信息。似乎？这就是正解？赶紧加进去试试。

final ConnectivityManager.NetworkCallback mNetworkCallback = new ConnectivityManager.NetworkCallback(ConnectivityManager.NetworkCallback.FLAG_INCLUDE_LOCATION_INFO) {
        @Override
        public void onAvailable(@NonNull Network network) {
            super.onAvailable(network);
        }

        @Override
        public void onCapabilitiesChanged(@NonNull Network network, @NonNull NetworkCapabilities networkCapabilities) {
            super.onCapabilitiesChanged(network, networkCapabilities);
            WifiInfo wifiInfo = (WifiInfo) networkCapabilities.getTransportInfo();
            if (wifiInfo != null) {
            String ssid = wifiInfo.getSSID().replace("\"", "").replace("<", "").replace(">", ""));
            } 
        }
    };

方法相同就是在创建NetworkCallback 时传入FLAG_INCLUDE_LOCATION_INFO。
编译，install，打开应用，ssid完美呈现。
至此问题解决，这就是正解。

总结

遇事不决阅读源码，百思不解可读源码。