使用KVC自定义UISearchBar的UI

KVC 如果名称错误会崩溃
按钮在输入文本没有获得响应者是isEnabled = false 的, 所以需要处理下
动态改变取消按钮文本有问题 待解决

self.searchBar.resignFirstResponder()
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now()+0.1) {
            (self.searchBar.value(forKey: "cancelButton") as! UIButton).isEnabled = true
        }
``` 

From: <http://www.jianshu.com/p/a4cfdcf0f7e1>

在日常工作中对于UISearchBar的操作主要集中在： 

  * 设置UISearchBar中textfiled的边框及圆角
  * 设置占位文字的大小及颜色
  * 设置输入文字的大小及颜色
  * 修改搜索图标
  * 修改取消按钮的文本
  * ....

实现的方式有很多，就设置边框而言：可以设置背景图片实现效果；或者直接用UITextField来代替UISearchBar等等。但是以上的操作主要是集中在UISearchBar内部的UITextField上，因此获取到UISearchBar内部的UITextField便可以实现以上的效果： 

  * 通过KVC获取子视图
    
    UISearchBar *searchBar = [[UISearchBar alloc]init];
    // 获取内部子视图
    UITextField *searchField = [searchBar valueForKey:@"_searchField"]; 
    UIView *backgroundView = [searchBar valueForKey:@"_background"];
    UIButton *cancelButton = [searchBar valueForKey:@"_cancelButton"];

  * 改变输入框文本
    
    UITextField *searchField = [searchBar valueForKey:@"_searchField"]; 
    
    // 设置输入文字的大小及颜色
    searchField.font = font(12);
    searchField.textColor = UIColorRgb(32,32,32);
    
    // 设置占位文字的大小及颜色
    [searchField setValue:UIColorRgb(197,197,197) forKeyPath:@"_placeholderLabel.textColor"];

  * 设置输入框边框及圆角
    
    UITextField *searchField = [searchBar valueForKey:@"_searchField"]; 
    
    // 设置边框及圆角
    searchField.layer.cornerRadius = 4.0f;
    searchField.layer.masksToBounds = YES;
    searchField.layer.borderWidth = 0.5f;
    searchField.layer.borderColor = UIColorRgbAlpha(95,96,108,0.2).CGColor;

  * 设置输入框内搜索图标
    
    UITextField *searchField = [searchBar valueForKey:@"_searchField"]; 
    
    // 设置searchField上的搜索图标
    UIImage *image = [UIImage imageNamed:@"search"];
    UIImageView *iView = [[UIImageView alloc] initWithImage:image];
    iView.frame = CGRectMake(0, 0, 15, 15);
    searchField.leftView = iView;

  * 改变取消按钮的title
    
    UIButton*cancelButton = [searchBar valueForKey:@"_cancelButton"]；
    [cancelButton setTitle:@"Close"forState:UIControlStateNormal];


---

KVC或者textField的clear属性

``` 
 UIButton *button = [textField valueForKey:@"_clearButton"];
   [button setImage:[UIImage imageNamed:@"icon_blueclear"] forState:UIControlStateNormal];

    field.clearButtonMode = UITextFieldViewModeWhileEditing;
    
    //swift 3
    let clearBtn = self.textField.value(forKey: "_clearButton") as! UIButton
            clearBtn.setImage(UIImage(named:"sy-ss"), for: UIControlState.normal)
            clearBtn.setImage(UIImage(named:"sy-ss"), for: UIControlState.highlighted)