Zebra蓝牙打印机仅在调试器下工作

Question

I am printing to a QLn420 and it's working great under the debugger or when very small amounts of ZPL are passed to it but it fails when I run the app not under the debugger. The code is basically the same as Zebra's demo code ( https://km.zebra.com/kb/index?page=content&id=WH122&actp=LIST ) except the dispatch_async is performed earlier in the callstack.

NSString *serialNumber = [ZebraPrintManager getBluetoothSerial];

// Instantiate connection to Zebra Bluetooth accessory
id<ZebraPrinterConnection, NSObject> thePrinterConn = [[MfiBtPrinterConnection alloc] initWithSerialNumber:serialNumber];

// Open the connection - physical connection is established here.
BOOL success = [thePrinterConn open];

NSError *error = nil;

// Send the data to printer as a byte array.
NSData* data = [ZPL dataUsingEncoding:NSUTF8StringEncoding];
success = success && [thePrinterConn write:data error:&error];

dispatch_async(dispatch_get_main_queue(), ^{
    if(success != YES || error != nil) {
        UIAlertView *errorAlert = [[UIAlertView alloc] initWithTitle:@"Error" message:[error localizedDescription] delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil];
        [errorAlert show];
    }
});

// Close the connection to release resources.
[thePrinterConn close];

Answer 1

There is a delay setting for Bluetooth. Increase this to at least 100. Some phones are not capable of using the value set to 30.