Zebra Printer only printing successive multiple labels if tapped by the user - ios

Question

I have a weird issue with Zebra printer. On the big picture, I have codes to fetch items to print one by one from the queue. So if when the printing initiated, and there's 3 items on the queue, the code will loop and fetch the first data in the queue, send it to the printer, and delete the first data in the queue. Sort of like dequeueing.
The problem is, if it's the code that looping and sending the data directly to the printer, the printer will only print the first item. The next item is gone, even though NSLog shows that the printer connection opened, data sent, printing successful, and printer connection closed, for every single item.
But if each time the code print one label, and then the app shows message box like "press OK to print next label", and then the user tap the OK button, it can print the second and the rest of the label after every tap of the button.
I have then tried to emulate this. I've tried to use timer to "push the button programmatically" [btnPrint sendActionsForControlEvents:UIControlEventTouchUpInside], I also use timer to call the function directly, or giving delay to the thread, but none works. It has to be initiated from a button which tapped from human touch. I don't know why.
Here's the code:
// main function to print
-(void) printLabel {
if ([dataToPrint count] > 0) {
[self printWithData:[dataToPrint objectAtIndex:0]];
}
}
-(void)printWithData:(NSString*) data;
{
NSString *zplString = data;
// do something with zplString
NSLog(#"Sending data to printer");
printHandler = [[PrintingHandler alloc] init];
[printHandler setDelegate:self];
[printHandler initialize];
[printHandler printToSerial:bluetoothSerialNumber withData:zplString];
}
// delegate to call if the print is success
-(void) printIsSuccess
{
[dataToPrint removeObjectAtIndex:0];
// in here, I just use sleep code instead of button tap emulation to avoid unnecessarily too long code
[NSThread sleepForTimeInterval:2.0f];
[self printLabel];
}
// this is method inside PrintingHandler class that get called by PrintingHandler (printToSerial:)
-(void) printLabelWithData:(NSString*) zplData toPrinter:(NSString*) serial withSender:(id) sender
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
// Instantiate connection to Zebra Bluetooth accessory
id<ZebraPrinterConnection, NSObject> thePrinterConn = [[MfiBtPrinterConnection alloc] initWithSerialNumber:serial];
// Open the connection - physical connection is established here.
BOOL success = [thePrinterConn open];
NSError *error = nil;
// Send the data to printer as a byte array.
success = success && [thePrinterConn write:[zplData dataUsingEncoding:NSUTF8StringEncoding] error:&error];
[NSThread sleepForTimeInterval:1.0f];
//Dispath GUI work back on to the main queue!
dispatch_async(dispatch_get_main_queue(), ^{
if (success != YES || error != nil) {
[delegate printFailed];
UIAlertView *errorAlert = [[UIAlertView alloc] initWithTitle:#"Error" message:[error localizedDescription] delegate:nil cancelButtonTitle:#"Ok" otherButtonTitles:nil];
[errorAlert show];
[errorAlert release];
}
else if (success != YES) {
NSLog(#"Print is not success, but no error raised");
[delegate printSuccess];
}
else
{
NSLog(#"Print is success");
[delegate printSuccess];
}
});
// Close the connection to release resources.
NSLog(#"printer connection closed");
[thePrinterConn close];
[thePrinterConn release];
});
}

Answer 1

Sorry, I've found the solution. The problem is it's too fast between opening the connection to the printer and sending data to the printer. I was putting some delay, but I put the delay at wrong position.
So the step to print currently is:
Open bluetooth printer connection
Send data
Delay
Close printer connection
When the correct one should be:
Open bluetooth printer connection
Delay
Send data
Close printer connection
Here I put the answer so this can help other people with same problem.
-(void) printLabelWithData:(NSString*) zplData toPrinter:(NSString*) serial withSender:(id) sender
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
// Instantiate connection to Zebra Bluetooth accessory
id<ZebraPrinterConnection, NSObject> thePrinterConn = [[MfiBtPrinterConnection alloc] initWithSerialNumber:serial];
// Open the connection - physical connection is established here.
BOOL success = [thePrinterConn open];
NSError *error = nil;
[NSThread sleepForTimeInterval:1.0f]; // this is the important one
// Send the data to printer as a byte array.
success = success && [thePrinterConn write:[zplData dataUsingEncoding:NSUTF8StringEncoding] error:&error];
//Dispath GUI work back on to the main queue!
dispatch_async(dispatch_get_main_queue(), ^{
if (success != YES || error != nil) {
[delegate printFailed];
UIAlertView *errorAlert = [[UIAlertView alloc] initWithTitle:#"Error" message:[error localizedDescription] delegate:nil cancelButtonTitle:#"Ok" otherButtonTitles:nil];
[errorAlert show];
[errorAlert release];
}
else if (success != YES) {
NSLog(#"Print is not success, but no error raised");
[delegate printSuccess];
}
else
{
NSLog(#"Print is success");
[delegate printSuccess];
}
});
// Close the connection to release resources.
NSLog(#"printer connection closed");
[thePrinterConn close];
[thePrinterConn release];
});
}