UITextView作为自己的委托意味着无限循环

Question

I have a subclass of a UITextView and I would like to make it it's own delegate. So that I can override the textView:shouldChangeTextInRange:replacementText: method, and prevent consecutive spaces being entered.

In [SATextView awakeFromNib] (SATextView is my subclass of UITextView), I do [self setDelegate:self]; . When I press on the textview to start editing everything freezes and eventually stops, and that backtrace shows that there has been an infinite loop.

It doesn't matter if I implement all delegate methods, just one, or none. Nor does it matter if those methods are empty.

Why does this cause an infinite loop? It only seems to happen if with UITextView (other objects you can subclass and set the delegate to self, and it won't have this problem). And how can I stop it? Or is there a better way to have this subclass not able to have consecutive spaces,

Answer 1

An idea... You could make a delegate Class that acts as a middle man between the real delegate and the UITextView (because you'll probably need to set the delegate after some time). So this new class will implement the delegate protocol, but it will also have a property for it's own delegate, so that you can forward textView:shouldChangeTextInRange:replacementText:, and still do the work of editing the spaces in your middleMan class.

Answer 2

It is possible to subscribe any numbers of observers to an object. So it is possible to subscribe itself:

@implementation MyTextView 

-(id) initWithFrame:(CGRect)frame // or initWithCoder: for loading from nib
{
    self = [super initWithFrame:frame];
    if(self) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textViewTextDidChangeNotification:) name:UITextViewTextDidChangeNotification object:self];
    }
    return self;
}

-(void)textViewTextDidChangeNotification:(NSNotification*)n
{
    self.text = [self.text stringByReplacingOccurrencesOfString:@"  " withString:@" "];
}

Answer 3

Here is an example of how I have successfully done this. I was only interested in preventing certain characters from being inputted so I only implement textView:shouldChangeTextInRange:replacementText: and then pass the rest on.

#import "INFTextView.h"

@interface INFTextView () <UITextViewDelegate>

@property (nonatomic, weak) id<UITextViewDelegate> externalDelegate;

@end

@implementation INFTextView

- (id)init {
    self = [super init];
    if (!self) {
        return nil;
    }

    self.delegate = self;

    return self;
}

- (void)awakeFromNib {
    self.delegate = self;
}

- (void)setDelegate:(id<UITextViewDelegate>)delegate {
    // we always want self to be the delegate, if someone is interested in delegate calls we will forward those on if applicable
    if (delegate == self) {
        [super setDelegate:self];
        return;
    } else {
        // capture that someone else is interested in delegate calls
        _externalDelegate = delegate;
    }
}

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text {
    NSCharacterSet *unsupportedCharacterSet = [[NSCharacterSet characterSetWithCharactersInString:kINFSupportedCharacters] invertedSet];

    NSRange unsupportedCharacterRange = [text rangeOfCharacterFromSet:unsupportedCharacterSet];
    if (unsupportedCharacterRange.location == NSNotFound) {
        return YES;
    } else {
        return NO;
    }
}

- (BOOL)textViewShouldBeginEditing:(UITextView *)textView {
    if ([_externalDelegate respondsToSelector:@selector(textViewShouldBeginEditing:)]) {
        return [_externalDelegate textViewShouldBeginEditing:textView];
    }

    return YES;
}

- (BOOL)textViewShouldEndEditing:(UITextView *)textView {
    if ([_externalDelegate respondsToSelector:@selector(textViewShouldEndEditing:)]) {
        return [_externalDelegate textViewShouldEndEditing:textView];
    }

    return YES;
}

- (void)textViewDidBeginEditing:(UITextView *)textView {
    if ([_externalDelegate respondsToSelector:@selector(textViewDidBeginEditing:)]) {
        [_externalDelegate textViewDidBeginEditing:textView];
    }
}

- (void)textViewDidEndEditing:(UITextView *)textView {
    if ([_externalDelegate respondsToSelector:@selector(textViewDidEndEditing:)]) {
        [_externalDelegate textViewDidEndEditing:textView];
    }
}

- (void)textViewDidChange:(UITextView *)textView {
    if ([_externalDelegate respondsToSelector:@selector(textViewDidChange:)]) {
        [_externalDelegate textViewDidChange:textView];
    }
}

- (void)textViewDidChangeSelection:(UITextView *)textView {
    if ([_externalDelegate respondsToSelector:@selector(textViewDidChangeSelection:)]) {
        [_externalDelegate textViewDidChangeSelection:textView];
    }
}

@end

One big 'gotcha' which led me to this question was I was trying to override delegate to return _externalDelegate but that caused some strange side effects (there must be internal code that depends on the actual delegate to be returned).