Why does shouldChangeTextInRange get called multip

问题:

The predictive-input of iOS8 calls the following delegate method of UITextView multiple times resulting in the selected word being inserted multiple times into the view.

This code works for typing single letters and copy/paste but not when using the predictive-input bar; why not?

- (BOOL) textView:(UITextView*)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString*)text
{
    textView.text = [textView.text stringByReplacingCharactersInRange:range withString:text];
    return false;
}

With this code; if I enter an empty UITextView and tap on "The" in the predictive text (autocomplete) view it inserts "The The" into the view by way of making three calls on this method. The parameters passed in for each call are:

• range : {0,0} text : @"The"
• range : {0,0} text : @"The"
• range : {3,0} text : @" "

The space I can understand; but why insert "The" twice?

回答1:

I got this same issue. It appears that with predictive text, setting textView.text in that delegate method triggers an immediate call to that delegate method again (this only happens with predictive text as far as I know).

I fixed it by just surrounding my textView changes with a guard:

private var hack_shouldIgnorePredictiveInput = false

func textView(textView: UITextView!, shouldChangeTextInRange range: NSRange, replacementText text: String!) -> Bool {
    if hack_shouldIgnorePredictiveInput {
        hack_shouldIgnorePredictiveInput = false
        return false
    }

    hack_shouldIgnorePredictiveInput = true

    textView.text = "" // Modify text however you need. This will cause shouldChangeTextInRange to be called again, but it will be ignored thanks to hack_shouldIgnorePredictiveInput

    hack_shouldIgnorePredictiveInput = false

    return false
}

回答2:

I modified the accepted answer from Richard Venable, because, as JLust noted in the comment, that 3rd call with the space was throwing me off.

I added

private var predictiveTextWatcher = 0

And

if predictiveTextWatcher == 1 {
            predictiveTextWatcher = 0
            return false
        }

        if hack_shouldIgnorePredictiveInput {
            predictiveTextWatcher += 1
            hack_shouldIgnorePredictiveInput = false
            return false
        }

It's all pretty hacky, but better than nothing.

Best,