• 思路分析:
  • 0.自定义UITextField
  • 1.设置占位文字的颜色找-->placeholderColor,结果发现UITextField没有提供这个属性
  • 2.在storyboard/xib中寻找设置placeholder的属性,也没有发现
  • 3.发现UITextField中有- (void)drawPlaceholderInRect:(CGRect)rect;,这个方法用到QuartzD中的知识,可以试试;
  • 4.打印UITextField的子控件,查看是否有设置placeholder的属性
  • 5.用运行时,查看UITextField中内部的结构,看有没有隐藏属性,利用KVC,可以强制使用任何私有属性
    -

方法一:

• 缺点:只能设置一次状态,不能动态的改变Placeholder的颜色

- (void)drawPlaceholderInRect:(CGRect)rect

{

    // 设置富文本属性

    NSMutableDictionary *dictM = [NSMutableDictionary dictionary];

    dictM[NSFontAttributeName] = self.font;

    dictM[NSForegroundColorAttributeName] = [UIColor redColor];

    CGPoint point = CGPointMake(0, (rect.size.height - self.font.lineHeight) * 0.5);

    [self.placeholder drawAtPoint:point withAttributes:dictM];

}

- (void)awakeFromNib

{

    DXLog(@"%@",self.subviews);

}

// 打印结果发现为空

// 猜测UITextField控件是懒加载的,调用这个方法的时候,它还没有加载storyboard/xib中的控件

// 利用GCD延时设置-->等storyboard/xib中的控件加载完毕在调用这个方法

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.01 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

        DXLog(@"%@",self.subviews);

    });

// 打印结果是数组,里面有`UITextFieldLabel`,好像没有多大用

利用运行时,查看UITextField中内部的结构

// 这个方法调用时刻:当一个控件从xib或者storyBoard中创建之前,就会调用这个方法

- (void)awakeFromNib

{

    unsigned int count = 0;

    Ivar *ivarList = class_copyIvarList([UITextField class], &count);

    for (int i = 0; i<count; i++) {

        Ivar ivar = ivarList[i];

        DXLog(@"%s",ivar_getName(ivar));

    }

    free(ivarList);

}

// 结果一大堆属性,其中有_placeholderLabel

// 利用KVC设置它颜色,结果成功

 UILabel *label = [self valueForKeyPath:@"_placeholderLabel"];

 label.textColor = [UIColor orangeColor];

方法二:有了placeholderLabel.textColor这个属性,在storyboard/xib中利用KVC设置placeholder颜色,如图

方法三:用 setAttributedPlaceholder方法

NSMutableDictionary *dict = [NSMutableDictionary dictionary];

dict[NSForegroundColorAttributeName] = [UIColor redColor];

NSAttributedString *attribute = [[NSAttributedString alloc] initWithString:self.placeholder attributes:dict];

[self setAttributedPlaceholder:attribute];

下面用四种方法,动态的设置placeholderLabel的颜色

方法一:addTarget

// 为了书写方便,便于管理,定义一个不可变的全局变量;

static NSString * const DXPlaceholderColorKey = @"placeholderLabel.textColor";

- (void)awakeFromNib

{

    [self addTarget:self action:@selector(editingDidBegin) forControlEvents:UIControlEventEditingDidBegin];

    [self addTarget:self action:@selector(editingDidEnd) forControlEvents:UIControlEventEditingDidEnd];

}

    - (void)editingDidBegin

{

    [self setValue:[UIColor whiteColor] forKeyPath:DXPlaceholderColorKey];

}

- (void)editingDidEnd

{

    [self setValue:[UIColor grayColor] forKeyPath:DXPlaceholderColorKey];

}

方法二:代理-->遵守协议,自己做自己的代理

- (void)awakeFromNib

{

    self.delegate = self;

}

#pragma mark -------- <UITextFieldDelegate>---------

- (void)textFieldDidBeginEditing:(UITextField *)textField

{

    [self setValue:[UIColor whiteColor] forKeyPath:DXPlaceholderColorKey];

}

- (void)textFieldDidEndEditing:(UITextField *)textField

{

    [self setValue:[UIColor grayColor] forKeyPath:DXPlaceholderColorKey];

}

方法三:通知

- (void)awakeFromNib

{

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(editingDidBegin) name:UITextFieldTextDidBeginEditingNotification object:self];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(editingDidEnd) name:UITextFieldTextDidEndEditingNotification object:self];

}

- (void)dealloc

{

    [[NSNotificationCenter defaultCenter] removeObserver:self];

}

- (void)editingDidBegin

{

    [self setValue:[UIColor whiteColor] forKeyPath:DXPlaceholderColorKey];

}

- (void)editingDidEnd

{

    [self setValue:[UIColor grayColor] forKeyPath:DXPlaceholderColorKey];

}

方法四:重写文本框特有的方法

- (void)awakeFromNib

{

    [self setValue:[UIColor grayColor] forKeyPath:DXPlaceholderColorKey];

}

- (BOOL)becomeFirstResponder

{

    [self setValue:[UIColor whiteColor] forKeyPath:DXPlaceholderColorKey];

    return [super becomeFirstResponder];

}

- (BOOL)resignFirstResponder

{

    [self setValue:[UIColor grayColor] forKeyPath:DXPlaceholderColorKey];

    return [super resignFirstResponder];

}