在ios中我们UITextField有Placeholder的功能,但是UITextView却没有这个方法,有时候我们也需要实现这样的Placeholder功能,StackOverFlow给我们提供了一个重写UITextView的方法,少量代码就实现了这个功能,值得学习一下。。
#import <UIKit/UIKit.h> @interface UIPlaceHolderTextView : UITextView @property (nonatomic, retain) NSString *placeholder; @property (nonatomic, retain) UIColor *placeholderColor; -(void)textChanged:(NSNotification*)notification; @end
#import "UIPlaceHolderTextView.h" @interface UIPlaceHolderTextView () @property (nonatomic, retain) UILabel *placeHolderLabel; @end @implementation UIPlaceHolderTextView CGFloat const UI_PLACEHOLDER_TEXT_CHANGED_ANIMATION_DURATION = 0.25; - (void)dealloc { [[NSNotificationCenter defaultCenter] removeObserver:self]; #if __has_feature(objc_arc) #else [_placeHolderLabel release]; _placeHolderLabel = nil; [_placeholderColor release]; _placeholderColor = nil; [_placeholder release]; _placeholder = nil; [super dealloc]; #endif } - (void)awakeFromNib { [super awakeFromNib]; // Use Interface Builder User Defined Runtime Attributes to set // placeholder and placeholderColor in Interface Builder. if (!self.placeholder) { [self setPlaceholder:@""]; } if (!self.placeholderColor) { [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; } [UIView animateWithDuration:UI_PLACEHOLDER_TEXT_CHANGED_ANIMATION_DURATION animations:^{ 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 = NSLineBreakByWordWrapping; _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
时间: 2024-10-11 02:26:50