本文介紹了NSAttributedString和NSMutableAttributedString的簡單用法.
一. NSAttributedString介紹
- 摘自NSAttributedString.h文件
@interface NSAttributedString : NSObject <NSCopying, NSMutableCopying, NSSecureCoding>
- 它由2部分組成
1.文字內容 :NSString *
2.文字屬性:NSDictionary *
文字顏色 - NSForegroundColorAttributeName
字體大小 - NSFontAttributeName
下劃線 - NSUnderlineStyleAttributeName
背景色 - NSBackgroundColorAttributeName
二.NSMutableAttributedString介紹
- 摘自NSAttributedString.h文件
@interface NSMutableAttributedString : NSAttributedString
- NSMutableAttributedString常用的有三種方法:
1.設置range范圍的屬性, 重復設置同一個范圍的屬性, 后面一次設置會覆蓋前面的設置.
- (void)setAttributes:(nullable NSDictionary<NSString *, id> *)attrs range:(NSRange)range;
2.添加range范圍的屬性, 同一個范圍, 可以不斷添加屬性.
- (void)addAttribute:(NSString *)name value:(id)value range:(NSRange)range;
3.一次性添加一個范圍內的多個屬性.
- (void)addAttributes:(NSDictionary<NSString *, id> *)attrs range:(NSRange)range;
三.需求
- 給文本框設置占位文字的字體顏色、背景顏色以及下劃線.
通過xib或者storyboard創建的界面,在界面右側是找不到對應的設置屬性.
四.解決
-
方法1.
通過NSAttributedString實現,自定義一個繼承至UITextField的類,在awakeFromNib方法中寫以下代碼.
NSMutableDictionary *attributes = [NSMutableDictionary dictionary];
attributes[NSForegroundColorAttributeName] = [UIColor yellowColor];
attributes[NSBackgroundColorAttributeName] = [UIColor redColor];
attributes[NSUnderlineStyleAttributeName] = @YES;
self.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"o惜樂o" attributes:attributes];
效果圖如下:
效果圖
- 注意 : 別忘記指定UITextField的Class
如圖:
關聯UITextField的Class
-
方法2:
通過NSMutableAttributedString實現.代碼如下:
NSMutableAttributedString *string = [[NSMutableAttributedString alloc] initWithString:@"o惜樂o"];
NSMutableDictionary *attributes = [NSMutableDictionary dictionary];
attributes[NSForegroundColorAttributeName] = [UIColor yellowColor];
attributes[NSBackgroundColorAttributeName] = [UIColor redColor];
attributes[NSUnderlineStyleAttributeName] = @YES;
[string setAttributes:attributes range:NSMakeRange(0, 4)];
self.attributedPlaceholder = string;
-
方法3:
NSMutableAttributedString *string = [[NSMutableAttributedString alloc] initWithString:@"o惜樂o"];
[string addAttribute:NSForegroundColorAttributeName value:[UIColor yellowColor] range:NSMakeRange(0, 4)];
[string addAttribute:NSBackgroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, 4)];
[string addAttribute:NSUnderlineStyleAttributeName value:@YES range:NSMakeRange(0, 4)];
self.attributedPlaceholder = string;
-
方法4:
重寫drawPlaceholderInRect方法
NSMutableDictionary *attributes = [NSMutableDictionary dictionary];
attributes[NSForegroundColorAttributeName] = [UIColor whiteColor];
attributes[NSBackgroundColorAttributeName] = [UIColor redColor];
attributes[NSFontAttributeName] = self.font;
attributes[NSUnderlineStyleAttributeName] = @YES;
CGPoint placeholderPoint = CGPointMake(0, (rect.size.height - self.font.lineHeight) * 0.5);
[self.placeholder drawAtPoint:placeholderPoint withAttributes:attributes];
-
方法5:
通過視圖分層可以看出,UITextField中包含UITextFieldLabel.
視圖分層
- 而占位視圖是通過什么來顯示呢?
根據self.subviews.lastObject.class,可知占位圖是通過UITextFieldLabel顯示的,根據self.subviews.lastObject.superClass可知UITextFieldLabel的父類是UILabel,所以可以使用.textColor方法去顯示文字顏色.但是,不能保證self.subviews.lastObject.class方法中取到的一定是UITextFieldLabel.所以運行時就上場了. - 因為UITextFieldLabel在UITextField.h頭文件中找不到具體內容,只是簡單的@class聲明一下,所以需要利用運行時,查看UITextField的成員變量或屬性,結果,你高興的發現了這個家伙 -- placeholderLabel,這時候可以理解為placeholderLabel屬性指向UITextFieldLabel所對應的內容,所以占位視圖也是placeholderLabel啦!!!那么,也可以通過
.textColor設置顏色.
unsigned int count;
Ivar *ivarList = class_copyIvarList([UITextField class], &count);
for (int i = 0; i < count; i++)
{
Ivar ivar = ivarList[i];
NSString *str = [NSString stringWithUTF8String:ivar_getName(ivar)];
NSLog(@"%@", str);
}
free(ivarList);
- 用KVC最終得出:
static NSString * const kPlaceholderColorKey = @"placeholderLabel.textColor";
static NSString * const kPlaceholderBGColorKey = @"placeholderLabel.backgroundColor";
[self setValue:[UIColor yellowColor] forKeyPath:kPlaceholderColorKey];
[self setValue:[UIColor redColor] forKeyPath:kPlaceholderBGColorKey];
設置下劃線無法用KCV實現,如果非要用,還是會繞回第一種寫法
NSMutableDictionary *attributes = [NSMutableDictionary dictionary];
attributes[NSUnderlineStyleAttributeName] = @YES;
NSAttributedString *attributeText = [[NSAttributedString alloc] initWithString:@"o惜樂o" attributes:attributes];
[self setValue:attributeText forKeyPath:kPlaceholderUnderLineKey];
- 說明:
UITextFieldLabel的父類為UILabel.UILabel中有TextColor屬性,而UILabel繼承自UIView,UIView中有backgroundColor屬性.所以UITextFieldLabel就可以設置文字顏色和背景顏色.而placeholderLabel是程序內部私有的屬性,指向UITextFieldLabel的內容,所以也能設置文字顏色和背景顏色.
