Android 网络连接是否可用的

在 Wifi 列表页看到了当前网络状态 Connected, no Internet,就跟进去看看系统是如何判断网络的可用性的。

http://androidxref.com/8.0.0_r4/xref/frameworks/base/packages/SettingsLib/res/values/strings.xml

<string name="wifi_connected_no_internet">Connected, no Internetstring>

Wifi 列表会刷新可连接的ap列表

http://androidxref.com/8.0.0_r4/xref/frameworks/base/packages/SettingsLib/src/com/android/settingslib/wifi/AccessPoint.java#1088

if (state == DetailedState.CONNECTED) {
    IWifiManager wifiManager = IWifiManager.Stub.asInterface(
            ServiceManager.getService(Context.WIFI_SERVICE));
    NetworkCapabilities nc = null;

    try {
        nc = cm.getNetworkCapabilities(wifiManager.getCurrentNetwork());
    } catch (RemoteException e) {}

    if (nc != null) {
        if (nc.hasCapability(nc.NET_CAPABILITY_CAPTIVE_PORTAL)) {
            return context.getString(
                com.android.internal.R.string.network_available_sign_in);
        } else if (!nc.hasCapability(NetworkCapabilities.NET_CAPABILITY_VALIDATED)) {
            return context.getString(R.string.wifi_connected_no_internet);
        }
    }
}

网络可用相当于

cm.activeNetworkInfo.isConnected && nc.hasCapability(NetworkCapabilities.NET_CAPABILITY_VALIDATED)

但测试了下 NetworkCapabilities 在部分机型是并不是很准，甚至完全不准- -