1.需求说明
项目中经常会遇到各种各样的需求，比如输入框透明，边框以及内部的placeholder为白色，再或者placeholder要求居中。
广大的iOS开发人员可能会想到各种方法，本人只举一些设置placeholder的颜色以及字体大小的常见用法。好，各位同行坐稳了,准备开车。
2 代码演示
2.1 iOS 6.0之前
//颜色设置
[self.textField setValue:color forKeyPath:@"_placeholderLabel.textColor"];
//字体大小
[self.textField setValue:[UIFont boldSystemFontOfSize:fontSize] forKeyPath:@"_placeholderLabel.font"];
设置placeholder的居中方式的时候，通过该方法设置如下，会报错，知道的大神可以帮忙晚上一下.
[textField setValue:[NSNumber numberWithInteger:NSTextAlignmentCenter] forKeyPath:@"_placeholderLabel.textAligment"];
2.2 iOS6之后 attributedPlaceholder属性
苹果官方文档原文对该属性的描述:
Discussion
This property is nil by default. If set, the placeholder string is drawn using a 70% gray color and the remaining style information (except the text color) of the attributed string. Assigning a new value to this property also replaces the value of the placeholder property with the same string data, albeit without any formatting information. Assigning a new value to this property does not affect any other style-related properties of the text field.
译文[1]
该属性默认是空的。如果设置了的话，如果设置了该属性，占位符( placeholder)会按照70%灰度颜色绘制，并按照富文本(attributed string)的样式信息保持样式（不包括文本颜色）。尽管没有任何的样式设置，但是给这个属性分配一个新的值会使用一个新的字符串数据替代占位符中的值。给该属性分配一个新的值并不会对输入框任何一个相关的样式属性造成影响。
在设置placeholder的对齐方式的时候也使用了NSMutableParagraphStyle类。
Overview
The NSMutableParagraphStyle class adds methods to its superclass, NSParagraphStyle, for changing the values of the subattributes in a paragraph style attribute.See the NSParagraphStyle and NSAttributedString specifications for more information.
译文[1]
这个NSMutableParagraphStyle类为它的父类NSParagraphStyle添加方法，用于在段落样式属性中改变子属性的值。更多了解，可以查看NSMutableParagraphStyle和NSAttributedString的说明。
_textField = [[UITextField alloc]initWithFrame:CGRectMake(24*HorizontalScale, 20*HorizontalScale+64, ScreenWidth - 48*HorizontalScale, 80*HorizontalScale)];
_textField.layer.borderColor = [UIColor lightGrayColor].CGColor;
_textField.layer.borderWidth = 1;
_textField.layer.cornerRadius = 4;
//设置光标起始位置
UIView *leftView = [[UIView alloc]initWithFrame:CGRectMake(0, 0,10,_textField.height )];
_textField.leftView = leftView;
_textField.leftViewMode = UITextFieldViewModeAlways;
CGRect frame = [@"输入楼盘名" boundingRectWithSize:CGSizeMake(MAXFLOAT, _textField.height) options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:14]} context:nil];
//设置textFiled的段落格式
NSMutableParagraphStyle *style = [_textField.defaultTextAttributes[NSParagraphStyleAttributeName] mutableCopy];
//设置垂直对齐
style.minimumLineHeight = _textField.font.lineHeight - (_textField.font.lineHeight - [UIFont systemFontOfSize:14.0].lineHeight) / 2.0;
//水平对齐
style.firstLineHeadIndent = (_textField.width - frame.size.width )*0.5 -DYNAMIC(20);
//设置placeholder的样式
_textField.attributedPlaceholder = [[NSAttributedString alloc]initWithString:@"输入楼盘名" attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:14],NSParagraphStyleAttributeName:style,NSForegroundColorAttributeName:[UIColor blueColor]
}];
[self.view addSubview:_textField];
