c_cpp 多行占位符文本视图

Posted 2021-05-14

#import "LCTextView.h"

@interface LCTextView()
@property (strong, nonatomic) UILabel *placeholderLabel;
@end

@implementation LCTextView

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    self.placeholderLabel = nil;
}

- (instancetype)initWithCoder:(NSCoder *)aDecoder
{
    if(self = [super initWithCoder:aDecoder]){
        self.contentOffset = CGPointZero;
        self.contentInset = UIEdgeInsetsZero;
        self.textContainerInset = UIEdgeInsetsMake(0,0,0,0);
        self.textContainer.lineFragmentPadding = 0;
        
        UILabel *placeholderLabel = [[UILabel alloc] init];
        placeholderLabel.translatesAutoresizingMaskIntoConstraints = NO;
        placeholderLabel.font = self.font;
        placeholderLabel.numberOfLines = 0;
        self.placeholderLabel = placeholderLabel;
        [self addSubview:placeholderLabel];

        NSArray *H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[label(==textView)]|" options:0 metrics:nil views:@{@"label": placeholderLabel, @"textView": self}];
        NSArray *V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[label]" options:0 metrics:nil views:@{@"label": placeholderLabel}];
        NSArray *constaints = [H arrayByAddingObjectsFromArray:V];
        [self addConstraints:constaints];
        
        [self _updatePlaceholderLabelUI:placeholderLabel text:@""];
        [self setPlaceholderColor:[UIColor lightGrayColor]];

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChangeNotifiaciton:) name:UITextViewTextDidChangeNotification object:self];
    }
    return self;
}

- (void)setText:(NSString *)text
{
	if([self.text isEqualToString:text]){
		return;
	}
	
	[self _updatePlaceholderLabelUI:self.placeholderLabel text:text];
	[super setText:text];
}

- (void)setPlaceholder:(NSString *)placeholder
{
    self.label.text = placeholder;
	[self _updatePlaceholderLabelUI:self.placeholderLabel text:self.text];
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor
{
    self.label.textColor = placeholderColor;
}

- (void)_updatePlaceholderLabelUI:(UILabel *)label text:(NSString *)text
{
    label.hidden = ![text isEqualToString:@""];
}

#pragma mark - Notification

- (void)textChangeNotifiaciton:(NSNotification *)n
{
	[self _updatePlaceholderLabelUI:self.placeholderLabel text:self.text];
}

@end

@interface LCTextView : UITextView
@property (strong, nonatomic) NSString *placeholder;
@property (strong, nonatomic) UIColor *placeholderColor;
- (void)textChangeNotifiaciton:(NSNotification *)n;
@end