Android实时获取热点已连接数(谷歌现成API可用，适用于第三方APP和系统APP)

public int getNumConnectedDevices() {
    return mNumConnectedDevices;
}

public void onNumClientsChanged(int numConnectedDevices) {
    mNumConnectedDevices = numConnectedDevices;
    fireHotspotChangedCallback(isHotspotEnabled(), numConnectedDevices);
}

public interface SoftApCallback {
    /**
     * Called when soft AP state changes.
     *
     * @param state new new AP state. One of {@link #WIFI_AP_STATE_DISABLED},
     *        {@link #WIFI_AP_STATE_DISABLING}, {@link #WIFI_AP_STATE_ENABLED},
     *        {@link #WIFI_AP_STATE_ENABLING}, {@link #WIFI_AP_STATE_FAILED}
     * @param failureReason reason when in failed state. One of
     *        {@link #SAP_START_FAILURE_GENERAL}, {@link #SAP_START_FAILURE_NO_CHANNEL}
     */
    public abstract void onStateChanged(@WifiApState int state,
            @SapStartFailure int failureReason);

    /**
     * Called when number of connected clients to soft AP changes.
     *
     * @param numClients number of connected clients
     */
    public abstract void onNumClientsChanged(int numClients);
}