iOS開發小技巧--自定義帶有占位文字的TextView(兩種方式)

自定義控件注意或框架注意:自己暴露在外面的屬性,一定要重寫setter,保證外界與內部的交互性

一.方案一:通過drawRect:方法將文字畫到textView中,監聽文字改變用的是通知中心(代理也可以監聽文字改變,但是這種方式就成了自己作為自己的代理了,不推薦這種方法)發出的消息

UITextViewTextDidChangeNotification.自己監聽通知.

• 對外界提供兩個屬性

• 內部實現

#import "ChaosPlaceholdTextView.h"

@implementation ChaosPlaceholdTextView

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChange) name:UITextViewTextDidChangeNotification object:nil];
        
        // 外界文字顏色不設置,默認為灰色
        self.placeholdColor = [UIColor grayColor];
    }
    return self;
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)textChange
{
    [self setNeedsDisplay];
}

// 調用drawRect時,會將之前的圖像擦除掉,重新繪制
- (void)drawRect:(CGRect)rect {
    
    if ([self hasText]) return;
    
    rect.origin.y += (64 + 7);
    rect.origin.x += 5;
    rect.size.width -= 2 * rect.origin.x;
    
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSForegroundColorAttributeName] = self.placeholdColor;
    attrs[NSFontAttributeName] = [UIFont systemFontOfSize:17];
    [self.placehold drawInRect:rect withAttributes:attrs];
}

// 設計框架需注意,給外界提供了屬性后,一定重寫出行的setter,這樣既可以時時監聽使用者對屬性的更改,還可以跟好的與外界代碼進行交互
- (void)setPlacehold:(NSString *)placehold
{
    _placehold = placehold;
    // 設置了站位文字后,需要重繪一遍
    [self setNeedsDisplay];
}

- (void)setPlaceholdColor:(UIColor *)placeholdColor
{
    _placeholdColor = placeholdColor;
    [self setNeedsDisplay];
}

// 同時,也要考慮到
- (void)setFont:(UIFont *)font
{
    [super setFont:font];
    
    [self setNeedsDisplay];
}

- (void)setText:(NSString *)text
{
    [super setText:text];
    
    [self setNeedsDisplay];
}

- (void)setAttributedText:(NSAttributedString *)attributedText
{
    [super setAttributedText:attributedText];
    
    [self setNeedsDisplay];
}

@end

• 缺點:由於是畫上去的,當設置了textView的alwaysBounceHorizontal屬性后,不能跟隨着scrollView的滑動而滑動,如下圖

方案二:通過給TextView添加一個Label,也是通過監聽文字改變的通知,修改label的hidden屬性.

#import "ChaosPlaceholdTextView.h"

@interface ChaosPlaceholdTextView()
/** 占位文字label */
@property (nonatomic, weak) UILabel *placeholderLabel;
@end

@implementation ChaosPlaceholdTextView

- (UILabel *)placeholderLabel
{
    if (!_placeholderLabel) {
        // 添加一個用來顯示占位文字的label
        UILabel *placeholderLabel = [[UILabel alloc] init];
        placeholderLabel.numberOfLines = 0;
        placeholderLabel.x = 4;
        placeholderLabel.y = 7;
        [self addSubview:placeholderLabel];
        _placeholderLabel = placeholderLabel;
    }
    return _placeholderLabel;
}

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        // 垂直方向上永遠有彈簧效果
        self.alwaysBounceVertical = YES;
        
        // 默認字體
        self.font = [UIFont systemFontOfSize:15];
        
        // 默認的占位文字顏色
        self.placeholderColor = [UIColor grayColor];
        
        // 監聽文字改變
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:nil];
    }
    return self;
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

/**
 * 監聽文字改變
 */
- (void)textDidChange
{
    // 只要有文字, 就隱藏占位文字label
    self.placeholderLabel.hidden = self.hasText;
}

/**
 * 更新占位文字的尺寸
 */
- (void)updatePlaceholderLabelSize
{
    CGSize maxSize = CGSizeMake(ChaosScreenW - 2 * self.placeholderLabel.x, MAXFLOAT);
    self.placeholderLabel.size = [self.placeholder boundingRectWithSize:maxSize options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName : self.font} context:nil].size;
}

#pragma mark - 重寫setter
- (void)setPlaceholderColor:(UIColor *)placeholderColor
{
    _placeholderColor = placeholderColor;
    
    self.placeholderLabel.textColor = placeholderColor;
}

- (void)setPlaceholder:(NSString *)placeholder
{
    _placeholder = [placeholder copy];
    
    self.placeholderLabel.text = placeholder;
    
    [self updatePlaceholderLabelSize];
}

- (void)setFont:(UIFont *)font
{
    [super setFont:font];
    
    self.placeholderLabel.font = font;
    
    [self updatePlaceholderLabelSize];
}

- (void)setText:(NSString *)text
{
    [super setText:text];
    
    [self textDidChange];
}

- (void)setAttributedText:(NSAttributedString *)attributedText
{
    [super setAttributedText:attributedText];
    
    [self textDidChange];
}

@end