Java setProcessDefaultNetwork始终返回false

我正在开发一款应用程序，它只在连接到移动数据网络时执行一些安全操作。我正试图让应用程序强制其所有网络流量通过特定网络，因此我正在查看在级别21中添加的api调用：

也为空

我还尝试了另一种方法，以防根据另一个答案网络不可用，所以我看到：

    ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
        NetworkRequest.Builder builder = new NetworkRequest.Builder();
        builder.addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET);
        builder.addTransportType(NetworkCapabilities.TRANSPORT_CELLULAR);
        NetworkCallback networkCallback = new NetworkCallback() {
            @Override
            public void onAvailable(Network network) {
                Log.d("ANDREW", "Network is available!");
                boolean result = ConnectivityManager.setProcessDefaultNetwork(network);
                Log.d("ANDREW", "RESULT: " + result);
                if (ConnectivityManager.getProcessDefaultNetwork() != null) {
                    Log.d("ANDREW", "Successfully set default network ");
                }
            }
        };
        NetworkRequest networkRequest = builder.build();
        connectivityManager.requestNetwork(networkRequest, networkCallback);
        connectivityManager.registerNetworkCallback(networkRequest, networkCallback);

我得到了isAvailable回调，但它仍然无法设置默认网络

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没有日志消息可供使用，我甚至查看了本机代码，但没有任何东西可以指出问题所在。SDK没有描述我能看到的任何额外步骤，所以我的问题是，为什么这总是返回false，开发人员应该做什么才能让它工作？我在Nexus 5和Nexus 6上都尝试过这一点。

我发现了它不起作用的原因，本机代码创建了一个套接字，该套接字也恰好需要INTERNET许可。SDK中未列出此权限，但您的应用程序需要此权限才能设置默认网络。

对于学分，可在此处找到替代方法问题：

Network defProcNetwork = ConnectivityManager.getProcessDefaultNetwork();

    ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
        NetworkRequest.Builder builder = new NetworkRequest.Builder();
        builder.addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET);
        builder.addTransportType(NetworkCapabilities.TRANSPORT_CELLULAR);
        NetworkCallback networkCallback = new NetworkCallback() {
            @Override
            public void onAvailable(Network network) {
                Log.d("ANDREW", "Network is available!");
                boolean result = ConnectivityManager.setProcessDefaultNetwork(network);
                Log.d("ANDREW", "RESULT: " + result);
                if (ConnectivityManager.getProcessDefaultNetwork() != null) {
                    Log.d("ANDREW", "Successfully set default network ");
                }
            }
        };
        NetworkRequest networkRequest = builder.build();
        connectivityManager.requestNetwork(networkRequest, networkCallback);
        connectivityManager.registerNetworkCallback(networkRequest, networkCallback);