• 使用属性

@property(nonatomic,copy)   NSAttributedString     *attributedPlaceholder;

// 文字属性
NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
attrs[NSForegroundColorAttributeName] = [UIColor grayColor];

// NSAttributedString : 带有属性的文字(富文本技术)
NSAttributedString *placeholder = [[NSAttributedString alloc] initWithString:@"手机号" attributes:attrs];
self.phoneField.attributedPlaceholder = placeholder;

NSMutableAttributedString *placehoder = [[NSMutableAttributedString alloc] initWithString:@"手机号"];
[placehoder setAttributes:@{NSForegroundColorAttributeName : [UIColor whiteColor]} range:NSMakeRange(0, 1)];
[placehoder setAttributes:@{
                            NSForegroundColorAttributeName : [UIColor yellowColor],
                            NSFontAttributeName : [UIFont systemFontOfSize:30]
                            } range:NSMakeRange(1, 1)];
[placehoder setAttributes:@{NSForegroundColorAttributeName : [UIColor redColor]} range:NSMakeRange(2, 1)];
self.phoneField.attributedPlaceholder = placehoder;

• 重写方法

- (void)drawPlaceholderInRect:(CGRect)rect
{
    [self.placeholder drawInRect:CGRectMake(0, 10, rect.size.width, 25) withAttributes:@{
                                                       NSForegroundColorAttributeName : [UIColor grayColor],
                                                       NSFontAttributeName : self.font}];
}

• 使用KVC

[self setValue:[UIColor grayColor] forKeyPath:@"_placeholderLabel.textColor"];

运行时(Runtime)

• 苹果官方一套C语言库
• 能做很多底层操作(比如访问隐藏的一些成员变量\成员方法....)
• 访问成员变量举例

unsigned int count = 0;

// 拷贝出所有的成员变量列表
Ivar *ivars = class_copyIvarList([UITextField class], &count);

for (int i = 0; i<count; i++) {
    // 取出成员变量
    // Ivar ivar = *(ivars + i);
    Ivar ivar = ivars[i];

    // 打印成员变量名字
    XMGLog(@"%s", ivar_getName(ivar));
}

// 释放
free(ivars);

ivars.png

- (void)awakeFromNib
{
    // 设置光标颜色和文字颜色一致
    self.tintColor = self.textColor;
    
    // 不成为第一响应者
    [self resignFirstResponder];
}

/**
 * 当前文本框聚焦时就会调用
 */
- (BOOL)becomeFirstResponder
{
    // 修改占位文字颜色
    [self setValue:self.textColor forKeyPath:@"_placeholderLabel.textColor"];
    return [super becomeFirstResponder];
}

/**
 * 当前文本框失去焦点时就会调用
 */
- (BOOL)resignFirstResponder
{
    // 修改占位文字颜色
    [self setValue:[UIColor grayColor] forKeyPath:@"_placeholderLabel.textColor"];
    return [super resignFirstResponder];
}