android get WIFI signal getConnectionInfo () problem

android wifi getConnectionInfo ()

WifiManager wifi_service = (WifiManager) getSystemService (WIFI_SERVICE);
WifiInfo wifiInfo = wifi_service.getConnectionInfo ();
if (wifiInfo.getBSSID ()! = null)
{
/ **** /
}

I DEBUG program, wifi_service is worth it. But a walk
WifiInfo wifiInfo = wifi_service.getConnectionInfo (); hung up.
So why a call getConnectionInfo () hung up.
WIFI is open.

Great God, please help thank you.

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