iOS疯狂详解之UITextView加上占位字符

//

//  SSTextView.h

//  SSToolkit

//

//  Created by Sam Soffes on 8/18/10.

//  Copyright 2010-2011 Sam Soffes. All rights reserved.

//

 

/**

 UITextView subclass that adds placeholder support like UITextField has.

 */

@interface SSTextView : UITextView

 

/**

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

 

 The default value is `nil`.

 */

@property (nonatomic, retain) NSString *placeholder;

 

/**

 The color of the placeholder.

 

 The default is `[UIColor lightGrayColor]`.

 */

@property (nonatomic, retain) UIColor *placeholderColor;

 

@end

 

 

//

//  SSTextView.m

//  SSToolkit

//

//  Created by Sam Soffes on 8/18/10.

//  Copyright 2010-2011 Sam Soffes. All rights reserved.

//

 

#import "SSTextView.h"

 

@interface SSTextView ()

- (void)_initialize;

- (void)_updateShouldDrawPlaceholder;

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

@end

 

 

@implementation SSTextView {

    BOOL _shouldDrawPlaceholder;

}

 

 

#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 release];

    _placeholder = [string retain];

 

    [self _updateShouldDrawPlaceholder];

}

 

 

#pragma mark - NSObject

 

- (void)dealloc {

    [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextViewTextDidChangeNotification object:self];

 

    [_placeholder release];

    [_placeholderColor release];

    [super dealloc];

}

 

 

#pragma mark - UIView

 

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

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

        [self _initialize];

    }

    return self;

}

 

 

- (id)initWithFrame:(CGRect)frame {

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

        [self _initialize];

    }

    return self;

}

 

 

- (void)drawRect:(CGRect)rect {

    [super drawRect:rect];

 

    if (_shouldDrawPlaceholder) {

        [_placeholderColor set];

        [_placeholder drawInRect:CGRectMake(8.0f, 8.0f, self.frame.size.width - 16.0f, self.frame.size.height - 16.0f) withFont:self.font];

    }

}

 

 

#pragma mark - Private

 

- (void)_initialize {

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(_textChanged:) name:UITextViewTextDidChangeNotification object:self];

 

    self.placeholderColor = [UIColor colorWithWhite:0.702f alpha:1.0f];

    _shouldDrawPlaceholder = NO;

}

 

 

- (void)_updateShouldDrawPlaceholder {

    BOOL prev = _shouldDrawPlaceholder;

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

 

    if (prev != _shouldDrawPlaceholder) {

        [self setNeedsDisplay];

    }

}

 

 

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

    [self _updateShouldDrawPlaceholder];   

}

 


@end



另外一种实现方式。

#import <Foundation/Foundation.h>

 

 

@interface UIPlaceHolderTextView : UITextView {

    NSString *placeholder;

    UIColor *placeholderColor;

 

@private

    UILabel *placeHolderLabel;

}

 

@property (nonatomic, retain) UILabel *placeHolderLabel;

@property (nonatomic, retain) NSString *placeholder;

@property (nonatomic, retain) UIColor *placeholderColor;

 

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

 

@end

 

//.m file

#import "UIPlaceHolderTextView.h"

 

 

@implementation UIPlaceHolderTextView

 

@synthesize placeHolderLabel;

@synthesize placeholder;

@synthesize placeholderColor;

 

- (void)dealloc

{

    [[NSNotificationCenter defaultCenter] removeObserver:self];

    [placeHolderLabel release]; placeHolderLabel = nil;

    [placeholderColor release]; placeholderColor = nil;

    [placeholder release]; placeholder = nil;

    [super dealloc];

}

 

- (void)awakeFromNib

{

    [super awakeFromNib];

    [self setPlaceholder:@""];

    [self setPlaceholderColor:[UIColor lightGrayColor]];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];

}

 

- (id)initWithFrame:(CGRect)frame

{

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

    {

        [self setPlaceholder:@""];

        [self setPlaceholderColor:[UIColor lightGrayColor]];

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];

    }

    return self;

}

 

- (void)textChanged:(NSNotification *)notification

{

    if([[self placeholder] length] == 0)

    {

        return;

    }

 

    if([[self text] length] == 0)

    {

        [[self viewWithTag:999] setAlpha:1];

    }

    else

    {

        [[self viewWithTag:999] setAlpha:0];

    }

}

 

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

    [super setText:text];

    [self textChanged:nil];

}

 

- (void)drawRect:(CGRect)rect

{

    if( [[self placeholder] length] > 0 )

    {

        if ( placeHolderLabel == nil )

        {

            placeHolderLabel = [[UILabel alloc] initWithFrame:CGRectMake(8,8,self.bounds.size.width - 16,0)];

            placeHolderLabel.lineBreakMode = UILineBreakModeWordWrap;

            placeHolderLabel.numberOfLines = 0;

            placeHolderLabel.font = self.font;

            placeHolderLabel.backgroundColor = [UIColor clearColor];

            placeHolderLabel.textColor = self.placeholderColor;

            placeHolderLabel.alpha = 0;

            placeHolderLabel.tag = 999;

            [self addSubview:placeHolderLabel];

        }

 

        placeHolderLabel.text = self.placeholder;

        [placeHolderLabel sizeToFit];

        [self sendSubviewToBack:placeHolderLabel];

    }

 

    if( [[self text] length] == 0 && [[self placeholder] length] > 0 )

    {

        [[self viewWithTag:999] setAlpha:1];

    }

 

    [super drawRect:rect];

}

 

@end