NSTextView not updating in a loop while writing to a USB device

Question

I am writing an Objective-C application which communicates with a USB device. The application writes certain data to the device continuously and displays the status of the write operation in a textView, which is an object of NSTextView. I call the -[NSTextView insertText:] method in the loop when I get the write operation status from the device.

The problem is that the NSTextView doesn't get updated at every call of -insertText:. I get the entire contents of the NSTextView only after the entire loop has been executed.

I didn't see an appropriate refresh or update method for NSTextView class. How can I recieve the status of the operation and update the NSTextView simultaneously?

- (IBAction)notifyContentHasChanged:(NSInteger) block {
    NSString *str;
    str = [NSString stringWithFormat:@"Block Written Successfully: %d\n", block];
    [data insertText:str];
}

- (IBAction)func {
    while(USB_SUCCESS(status))
    {
        printf("\nBlocks Written Successfully: %d",BlockCnt);
        [refToSelf notifyContentHasChanged:BlockCnt];
    }
}

Note that the printf on console is updated timely but not the NSTextView.

Answer 1

Mac OS X does not flush changes to views to the screen immediately, to avoid the flicker and tearing that's common in such situations. This means you can't just sit in a loop and perform blocking operations while you update a view; if you do this, neither the view nor anything else in your application's human interface will update, and your application will appear hung and eventually get the spinning cursor.

(The spinning cursor appears when an application hasn't communicated with the window server after a small amount of time; there is no way to suppress this, by design. It doesn't mean "wait," it means "this application has gone off into the weeds" and you should strive to ensure it never appears for your users.)

To manage blocking operations in Cocoa, you can do one of two things:

1. You can perform the blocking operations in a background thread and communicate the results to the main thread for updating your human interface. For example, you can do I/O or socket communications this way using select(2) and the standard UNIX file I/O calls.

2. You can schedule the operations on a run loop (such as the main run loop) if a compatible version is available; this will typically manage a background thread for the blocking version of the operation for you. For example, NSFileHandle provides a run loop compatible abstraction atop file descriptors; NSStream does this for socket communications as well.

Answer 2

The problem is solved. It required displayIfNeeded() method of the NSView class.

Answer 3

You should be able to refresh the NSTextView via the -setNeedsDisplay: method.

Answer 4

I have a loop that is accessing data off the 'net and stuffing it in a db. As I'm processing, I would like a console-like window (not the one in Xcode since this would be a compiled app.)

So I have a NSTextView that I'm changing the textStorage of and scrolling to the bottom each time through the loop. Unfortunately, the only visible changes occur when the loop is finished (though correctly.)

Is there some kind of simple "OK, update the screen now" method without having to get low level or writing much more code?