Question

I use the following code to simulate a key press in a UITextView (and also to set the scroll to the insertion position):

NSRange selectedRange = textview.selectedRange;

NSString *currentText = textview.text;

NSString *yourString = @"x";

NSString *firstPart = [currentText substringToIndex: selectedRange.location];
NSString *lastPart = [currentText substringFromIndex: selectedRange.location];

NSString *modifiedText = [firstPart stringByAppendingFormat:@"%@%@", yourString, lastPart];

textview.text = modifiedText;

NSInteger loc = selectedRange.location + 1;
NSInteger len = textview.selectedRange.length;

NSRange newRange = NSMakeRange(loc, len);
textview.selectedRange = newRange;

As you can see, i divide the textview.text, i insert the @”x” in the cursor position and i modify the whole text. This works great, as a matter of fact, unless the length of the text file is big. And this sounds logical, given that i divide the whole thing in parts and so with every simulated key.

So with a small text file i have no problem whatsoever, but with a big one i can see a considerable lag.

Is there any way to do this with a better performance?

Answer 1

Instead of rewriting the whole text at each keystroke, you should use the
-(void)insertText:(NSString*)text method

Sample code from here:

@interface UIResponder(UIResponderInsertTextAdditions)
- (void) insertText: (NSString*) text;
@end

@implementation UIResponder(UIResponderInsertTextAdditions)

- (void) insertText: (NSString*) text
{
    // Get a refererence to the system pasteboard because that's
    // the only one @selector(paste:) will use.
    UIPasteboard* generalPasteboard = [UIPasteboard generalPasteboard];

    // Save a copy of the system pasteboard's items
    // so we can restore them later.
    NSArray* items = [generalPasteboard.items copy];

    // Set the contents of the system pasteboard
    // to the text we wish to insert.
    generalPasteboard.string = text;

    // Tell this responder to paste the contents of the
    // system pasteboard at the current cursor location.
    [self paste: self];

    // Restore the system pasteboard to its original items.
    generalPasteboard.items = items;

    // Free the items array we copied earlier.
    [items release];
}

@end