TextView添加placeholder属性

@interface SSTextView : UITextView  {

    BOOL _shouldDrawPlaceholder;

}

 

 

/**

 The string that is displayed when there is no other text in the text view.

 

 The default value is `nil`.

 */

@property (nonatomic) NSString *placeholder;

 

/**

 The color of the placeholder.

 

 The default is `[UIColor lightGrayColor]`.

 */

@property (nonatomic) UIColor *placeholderColor;

 

 

@end

 

 

 

 

#import "SSTextView.h"

 

@interfaceSSTextView ()

- (void)_initialize;

- (void)_updateShouldDrawPlaceholder;

- (void)_textChanged:(NSNotification *)notification;

@end

 

 

@implementation SSTextView

 

#pragma mark - Accessors

 

@synthesize placeholder = _placeholder;

@synthesize placeholderColor = _placeholderColor;

 

- (void)setText:(NSString *)string {

    [super setText:string];

    [self_updateShouldDrawPlaceholder];

}

 

 

- (void)setPlaceholder:(NSString *)string {

    if ([string isEqual:_placeholder]) {

        return;

    }

    

    _placeholder = string;

    

    [self_updateShouldDrawPlaceholder];

}

 

 

#pragma mark - NSObject

 

- (void)dealloc {

    [[NSNotificationCenterdefaultCenter] removeObserver:selfname:UITextViewTextDidChangeNotificationobject:self];

    

}

 

 

#pragma mark - UIView

 

- (id)initWithCoder:(NSCoder *)aDecoder {

    if ((self = [super initWithCoder:aDecoder])) {

        [self _initialize];

    }

    returnself;

}

 

 

- (id)initWithFrame:(CGRect)frame {

    if ((self = [super initWithFrame:frame])) {

        [self _initialize];

    }

    returnself;

}

 

 

- (void)drawRect:(CGRect)rect {

    [super drawRect:rect];

    

 - (void)drawRect:(CGRect)rect {

    [super drawRect:rect];

    

    if (_shouldDrawPlaceholder) {

        [_placeholderColorset];

        

        [_placeholderdrawInRect:CGRectMake(8.0f, 5.0f, self.frame.size.width - 16.0f, self.frame.size.height - 16.0f) withAttributes:[NSDictionarydictionaryWithObject:self.placeholderColorforKey:NSForegroundColorAttributeName]];

        

    }

}

}

 

 

#pragma mark - Private

 

- (void)_initialize {

    [[NSNotificationCenterdefaultCenter] addObserver:selfselector:@selector(_textChanged:) name:UITextViewTextDidChangeNotificationobject:self];

    

    self.placeholderColor = [UIColorcolorWithWhite:0.702falpha:1.0f];

    _shouldDrawPlaceholder = NO;

}

 

 

- (void)_updateShouldDrawPlaceholder {

    BOOL prev = _shouldDrawPlaceholder;

    _shouldDrawPlaceholder = self.placeholder && self.placeholderColor && self.text.length == 0;

    

    if (prev != _shouldDrawPlaceholder) {

        [selfsetNeedsDisplay];

    }

}

 

 

- (void)_textChanged:(NSNotification *)notificaiton {

    [self_updateShouldDrawPlaceholder];    

}

 

 

@end