iOS开发之在列表上方添加水印的方法

#import <UIKit/UIKit.h>

@interface watermarkView : UIImageView

/**
 设置水印

 @param frame 水印大小
 @param markText 水印显示的文字
 */
- (instancetype)initWithFrame:(CGRect)frame WithText:(NSString *)markText;

@end

#import "watermarkView.h"

#define HORIZONTAL_SPACE 30//水平间距
#define VERTICAL_SPACE 50//竖直间距
#define CG_TRANSFORM_ROTATION (M_PI_2 / 3)//旋转角度(正旋45度 || 反旋45度)

@implementation watermarkView

- (instancetype)initWithFrame:(CGRect)frame WithText:(NSString *)markText{
 if(self = [super initWithFrame:frame]){
  
  UIFont *font = [UIFont systemFontOfSize:14];
  
  UIColor *color = YTHColorAlpha(152, 152, 152, 0.1);
  
  //原始image的宽高
  CGFloat viewWidth = frame.size.width;
  CGFloat viewHeight = frame.size.height;
  
  //为了防止图片失真，绘制区域宽高和原始图片宽高一样
  UIGraphicsBeginImageContext(CGSizeMake(viewWidth, viewHeight));
  
  //sqrtLength：原始image的对角线length。在水印旋转矩阵中只要矩阵的宽高是原始image的对角线长度，无论旋转多少度都不会有空白。
  CGFloat sqrtLength = sqrt(viewWidth*viewWidth + viewHeight*viewHeight);
  //文字的属性
  NSDictionary *attr = @{
        //设置字体大小
        NSFontAttributeName: font,
        //设置文字颜色
        NSForegroundColorAttributeName :color,
        };
  NSString* mark = markText;
  NSMutableAttributedString *attrStr = [[NSMutableAttributedString alloc] initWithString:mark attributes:attr];
  //绘制文字的宽高
  CGFloat strWidth = attrStr.size.width;
  CGFloat strHeight = attrStr.size.height;
  
  //开始旋转上下文矩阵，绘制水印文字
  CGContextRef context = UIGraphicsGetCurrentContext();
  
  //将绘制原点（0，0）调整到原image的中心
  CGContextConcatCTM(context, CGAffineTransformMakeTranslation(viewWidth/2, viewHeight/2));
  //以绘制原点为中心旋转
  CGContextConcatCTM(context, CGAffineTransformMakeRotation(CG_TRANSFORM_ROTATION));
  //将绘制原点恢复初始值，保证当前context中心和源image的中心处在一个点(当前context已经旋转，所以绘制出的任何layer都是倾斜的)
  CGContextConcatCTM(context, CGAffineTransformMakeTranslation(-viewWidth/2, -viewHeight/2));
  
  //计算需要绘制的列数和行数
  int horCount = sqrtLength / (strWidth + HORIZONTAL_SPACE) + 1;
  int verCount = sqrtLength / (strHeight + VERTICAL_SPACE) + 1;
  
  //此处计算出需要绘制水印文字的起始点，由于水印区域要大于图片区域所以起点在原有基础上移
  CGFloat orignX = -(sqrtLength-viewWidth)/2;
  CGFloat orignY = -(sqrtLength-viewHeight)/2;
  
  //在每列绘制时X坐标叠加
  CGFloat tempOrignX = orignX;
  //在每行绘制时Y坐标叠加
  CGFloat tempOrignY = orignY;
  for (int i = 0; i < horCount * verCount; i++) {
   [mark drawInRect:CGRectMake(tempOrignX, tempOrignY, strWidth, strHeight) withAttributes:attr];
   if (i % horCount == 0 && i != 0) {
    tempOrignX = orignX;
    tempOrignY += (strHeight + VERTICAL_SPACE);
   }else{
    tempOrignX += (strWidth + HORIZONTAL_SPACE);
   }
  }
  //根据上下文制作成图片
    UIImage *finalImg = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  CGContextRestoreGState(context);
  
  self.image = finalImg;
 }
 
 return self;
}

-(UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event{
 
 //1.判断自己能否接收事件
 if(self.userInteractionEnabled == NO || self.hidden == YES || self.alpha <= 0.01) {
  return nil;
 }
 //2.判断当前点在不在当前View.
 if (![self pointInside:point withEvent:event]) {
  return nil;
 }
 //3.从后往前遍历自己的子控件.让子控件重复前两步操作,(把事件传递给,让子控件调用hitTest)
 int count = (int)self.subviews.count;
 for (int i = count - 1; i >= 0; i--) {
  //取出每一个子控件
  UIView *chileV = self.subviews[I];
  //把当前的点转换成子控件坐标系上的点.
  CGPoint childP = [self convertPoint:point toView:chileV];
  UIView *fitView = [chileV hitTest:childP withEvent:event];
  //判断有没有找到最适合的View
  if(fitView){
   return fitView;
  }
 }
 
 //4.没有找到比它自己更适合的View.那么它自己就是最适合的View
 return self;
}

//作用:判断当前点在不在它调用View,(谁调用pointInside,这个View就是谁)
//什么时候调用:它是在hitTest方法当中调用的.
//注意:point点必须得要跟它方法调用者在同一个坐标系里面
-(BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event{
 NSLog(@"%s",__func__);
 return NO;
}

 //加水印
 watermarkView *watermark = [[watermarkView alloc] initWithFrame:CGRectMake(0, 0, KScreenW, KScreenH) WithText:@"测试"];
 [self.view addSubview:watermark];