iOS开发 UITextField Category 设置placeHolder字体以及颜色

方法一：
新建一category
.h文件

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface UITextField (ZKChangePlacholder)

- (void)setPlaceholderFont:(UIFont *)font;
- (void)setPlaceholderTextColor:(UIColor *)color;
- (void)setPlaceholderFont:(UIFont *)font textColor:(UIColor *)color;

@end

NS_ASSUME_NONNULL_END

.m文件

#import "UITextField+ZKChangePlacholder.h"
 
@implementation UITextField (ZKChangePlacholder)

- (void)setPlaceholderFont:(UIFont *)font{
    [self setPlaceholderFont:font textColor:nil];
}
- (void)setPlaceholderTextColor:(UIColor *)color{
    [self setPlaceholderFont:nil textColor:color];
}
- (void)setPlaceholderFont:(UIFont *)font textColor:(UIColor *)color{
    if (!self.placeholder || [[self.placeholder stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0) {
        return;
    }
    NSMutableAttributedString *mutAttStr = [[NSMutableAttributedString alloc]initWithString:self.placeholder];
    if (font) {
        [mutAttStr addAttribute:NSFontAttributeName value:font range:NSMakeRange(0, self.placeholder.length)];
    }
    if (color) {
        [mutAttStr addAttribute:NSForegroundColorAttributeName value:color range:NSMakeRange(0, self.placeholder.length)];
    }
    [self setAttributedPlaceholder:mutAttStr];
}

@end

使用

[textField setPlaceholderFont:[UIFont xxxxxx]textColor:[UIColor xxxxxx]];

方法二：

 UITextField *textField = [[UITextField alloc] init];
 textField.frame = CGRectMake(100, 100,200, 40);
 textField.borderStyle = UITextBorderStyleRoundedRect; // 边框类型
 textField.font = [UIFont systemFontOfSize:14];
 // 就下面这两行是重点
 NSAttributedString *attrString = [[NSAttributedString alloc] initWithString:@"请输入占位文字" attributes:
        @{NSForegroundColorAttributeName:[UIColor redColor],
                     NSFontAttributeName:textField.font,
          NSBackgroundColorAttributeName:[UIColor yellowColor]
             }];
    
  
 textField.attributedPlaceholder =attrString;
 [self.view addSubview:textField];

方法三：
自定义一个 XXTextField 继承自 UITextField；
重写自定义 XXTextField 的 drawPlaceholderInRect: 方法；
在 drawPlaceholderInRect 方法中设置 placeholder 的属性。

- (void)drawPlaceholderInRect:(CGRect)rect {
    
    // 计算占位文字的 Size
    NSDictionary *attributes = @{
                                 NSForegroundColorAttributeName : [UIColor redColor],
                                 NSFontAttributeName : [UIFont systemFontOfSize:20]
                                 };
    CGSize placeholderSize = [self.placeholder sizeWithAttributes:attributes];
    
    [self.placeholder drawInRect:CGRectMake(0, (rect.size.height - placeholderSize.height)/2, rect.size.width, rect.size.height) withAttributes: attributes];
}

方法四：
利用 Runtime，找到并修改 UITextfield 的私有属性

实现步骤：
通过获取类的属性列表和成员变量列表的方法打印 UITextfield 所有属性和成员变量；
找到私有的成员变量 _placeholderLabel；
利用 KVC 对 _placeholderLabel 进行修改。

// 打印 UITextfield 的所有属性和成员变量
- (void)printUITextFieldList {
    unsigned int count;
    
    Ivar *ivarList = class_copyIvarList([UITextField class], &count);
    for (unsigned int i = 0; i < count; i++) {
        Ivar myIvar = ivarList[i];
        const char *ivarName = ivar_getName(myIvar);
        NSLog(@"ivar(%d) : %@", i, [NSString stringWithUTF8String:ivarName]);
    }
    
    free(ivarList);
    
    objc_property_t *propertyList = class_copyPropertyList([UITextField class], &count);
    for (unsigned int i = 0; i < count; i++) {
        const char *propertyName = property_getName(propertyList[i]);
        NSLog(@"propertyName(%d) : %@", i, [NSString stringWithUTF8String:propertyName]);
    }
    
    free(propertyList);
}

// 通过修改 UITextfield 的私有属性更改占位颜色和字体
- (void)createLoginTextField {
    UITextField *loginTextField = [[UITextField alloc] init];
    loginTextField.frame = CGRectMake(15,(self.view.bounds.size.height-52-50)/2, self.view.bounds.size.width-60-18,52);
    loginTextField.delegate = self;
    loginTextField.font = [UIFont systemFontOfSize:14];
    loginTextField.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
    loginTextField.textColor = [UIColor blackColor];
    
    loginTextField.placeholder = @"用户名/邮箱";
    [loginTextField setValue:[UIFont systemFontOfSize:15] forKeyPath:@"_placeholderLabel.font"];
    [loginTextField setValue:[UIColor lightGrayColor]forKeyPath:@"_placeholderLabel.textColor"];
    
    [self.view addSubview:loginTextField];
}

补充，使用runtime在iOS13系统下会报错如下图

iOS13系统下报错

解决方法：

    //获取一个实例变量信息
    Ivar ivar = class_getInstanceVariable([UITextField class], "_placeholderLabel");
    //获取成员变量的值
    UILabel *placeLabel = object_getIvar(textField, ivar);
    placeLabel.textColor = [UIColor systemPinkColor];
    placeLabel.font = [UIFont systemFontOfSize:18];

最后一方法转自于此篇华文：https://www.jianshu.com/p/aeecc4b4621c