Set selectedRange when NSTextField becomes focused

Question

I'm overriding becomeFirstResponder to know when my NSTextField is focused. Once focused, I'm trying to move the cursor to the end. The following snippet does not work:

@interface MyTextField : NSTextField
@end

@implementation MyTextField

- (BOOL)becomeFirstResponder
{
  if ([super becomeFirstResponder]) {
    self.currentEditor.selectedRange = NSMakeRange(self.stringValue.length, 0);
    return YES;
  }
  return NO;
}

@end

By overriding textView:didChangeSelection:, I found that the selection is made, but it's then overwritten by some internal code that runs in response to the NSEventTypeLeftMouseDown event.

The logs look like this:

location=0, length=25

location=25, length=0 // The desired selection.

location=0, length=0

location=5, length=0 // Where the user clicked.

Answer 1

Override the mouseDown: method in your NSTextField subclass.

Then, set selectedRange after calling super.

- (void)mouseDown:(NSEvent *)event
{
  [super mouseDown:event];
  self.currentEditor.selectedRange = NSMakeRange(self.stringValue.length, 0);
}

NSTextField only has its mouseDown: method called when its "field editor" is not yet focused, so the user can still change the selection after the NSTextField gains focus.

This isn't a perfect solution, because the user may have focused the NSTextField indirectly (eg: with the Tab key). You can always set selectedRange in both mouseDown: and becomeFirstResponder though.

Answer 2

Use performSelector:withObject:afterDelay: from inside becomeFirstResponder to ensure the selectedRange is set after the NSEventTypeLeftMouseDown event is handled.

- (BOOL)becomeFirstResponder
{
  if ([super becomeFirstResponder]) {
    [self performSelector:@selector(textFieldDidFocus) withObject:nil afterDelay:0.0];
    return YES;
  }
  return NO;
}

- (void)textFieldDidFocus
{
  self.currentEditor.selectedRange = NSMakeRange(self.stringValue.length, 0);
}