通過NSAttributeString方法來更改占位文字的屬性
(void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
//文字屬性
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
dict[NSForegroundColorAttributeName] = [UIColor grayColor];
//帶有屬性的文字（富文本屬性）NSAttributeString
NSAttributedString *attr = [[NSAttributedString alloc] initWithString:@"手機號" attributes:dict];
self.phoneField.attributedPlaceholder = attr;
} 

//畫出占位文字- (void)drawPlaceholderInRect:(CGRect)rect {
[self.placeholder drawInRect:CGRectMake(0, 13, self.size.width, 25) withAttributes:@{
NSForegroundColorAttributeName : [UIColor grayColor],
NSFontAttributeName : [UIFont systemFontOfSize:14]
}];
}

(void)initialize {
unsigned int count = 0;
Ivar *ivars = class_copyIvarList([UITextField class] , &count);
for (int i = 0; i < count; i++) {
//取出成員變量
Ivar ivar = *(ivars + i);
//打印成員變量名字
DDZLog(@"%s",ivar_getName(ivar));
}
}

- (void)awakeFromNib {
//修改占位文字顏色
[self setValue:[UIColor grayColor] forKeyPath:@"_placeholderLabel.textColor"]; //設置光標顏色和文字顏色一致
self.tintColor = self.textColor;
}

//獲得焦點時
- (BOOL)becomeFirstResponder {
//改變占位文字顏色
[self setValue:self.textColor forKeyPath:@"_placeholderLabel.textColor"]; return [super becomeFirstResponder];
}
//失去焦點時
- (BOOL)resignFirstResponder {
//改變占位文字顏色
[self setValue:[UIColor grayColor] forKeyPath:@"_placeholderLabel.textColor"]; return [super resignFirstResponder];
}