UIView on UITouch 中的擦除函数

Question

我有两个UIView一个在另一个之上，第一个有红色作为backgroundColor，而上面的一个有白色作为backgroundColor，当用户触摸和着色上部UIVIEW下UIView必须可见..这里可能吗...？？

Answer 1

是的，这是可能的，我也在我的项目中这样做了。看看这个链接

希望这对你想做的事情有所帮助;-）

Answer 2

我有针对您此要求的类代码.. 只是尝试理解流程

创建一个像下面这样的UIView类...

请参阅下面的TouchView.h文件..

   //
//  TouchView.h
//
//  Created by Paras Joshi on 23/08/12..
//
#import <UIKit/UIKit.h>
@interface TouchView : UIView {
    // array of all the touch locations
    NSMutableArray *points;
    // image to mask on user gesture
    UIImage *maskImage;
}
@property (nonatomic, retain) UIImage *maskImage;
@property (nonatomic, retain) NSMutableArray *points;
-(void)drawPic:(UIImage *)thisPic;
@end

还有像波纹管这样的TouchView.m文件。

 //  TouchView.m
//
//  Created by Paras Joshi on 23/08/12..
#import "TouchView.h"
// Define method POINT to return the CGPoint value of the object at self.points[index] 
#define POINT(index)    [[self.points objectAtIndex:index] CGPointValue];


@interface TouchView (PrivateMethods)
    -(void)clipImage;
    @end

    @implementation TouchView
    @synthesize points,maskImage;
    // mask will be a sphere of maskWidth X maskHeight
    float maskWidth = 30.0f;
    float maskHeight = 30.0f;

    - (id)initWithFrame:(CGRect)frame {
        self = [super initWithFrame:frame];
        if (self) {
            // Initialization code.
            self.backgroundColor = [UIColor clearColor];
            self.points = [NSMutableArray array];
            // set the 'maskImage'
            maskImage = [[UIImage alloc]init];
    //      maskImage = [UIImage imageNamed:@"house1.jpeg"];
            // listen for 'reset' notification event
    //      [[NSNotificationCenter defaultCenter] addObserver:self
    //                                               selector:@selector(reset:)
    //                                                   name:ResetNotification
    //                                                 object:nil];
        }
        return self;
    }
    -(void)drawPic:(UIImage *)thisPic {
        maskImage = thisPic;
        [maskImage retain];
        [self setNeedsDisplay];
    }
    -(void)reset:(NSNotification *)notification{
        [self.points removeAllObjects];
        [self setNeedsDisplay];
    }
    -(void)drawRect:(CGRect)rect{
        // break if there are no points to mask
        if (!self.points || self.points.count < 2) return; 
        // mask the image
        [self clipImage];
    }
    // clipImage handles creating and adding a path of masks (ellipses), to our drawing context (display) based on gesture input
    - (void) clipImage{
        // grab a reference to the image we're going to mask
        UIImage *image = maskImage;
        // determine the extents of the image so that we do not 
        // do unnecessary drawing ouside the image bounds
    //  CGRect bounds = CGRectMake(0.0f, 0.0f, maskImage.size.width, maskImage.size.height);
        CGRect bounds = CGRectMake(0.0f, 0.0f, 1024, 694);  
        // get the graphics context and init a path to draw our mask to
        CGContextRef context = UIGraphicsGetCurrentContext();
        CGMutablePathRef path = CGPathCreateMutable();
        // add ellipses to every CGPoint in self.points
        for(int i = 0; i < self.points.count - 1; i++){
            // get the CGPoint value stored in self.points[i]
            CGPoint pt = POINT(i);
            // add the ellipse at that point
            CGPathAddEllipseInRect(path, NULL, CGRectMake(pt.x - (maskWidth / 2), pt.y - (maskHeight / 2), maskWidth, maskHeight));
        }
        // add the path of ellipses to our drawing context
        CGContextAddPath(context, path);
        // clip the Core Graphics drawing context to our display
        CGContextClip(context);
        // now add the image to our display (it will only appear wherever the CGPoints of self.points are located)
        [image drawInRect:bounds];
        // finalize drawing
        CGContextClosePath(context);
    }

    - (void)dealloc {
        points = nil;
        // remove event listener
        [[NSNotificationCenter defaultCenter] removeObserver:self];
        [super dealloc];
    }

    #pragma mark -
    #pragma mark Gesture Methods
    -(BOOL) isMultipleTouchEnabled{ return NO; };       
    -(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
        // get the location of the touch
        CGPoint pt = [[touches anyObject] locationInView:self];
        // puch the touch location (pt) onto our array of points
        [self.points addObject:[NSValue valueWithCGPoint:pt]];
        // update display by calling it's 'drawRect' method
        [self setNeedsDisplay];
    }
    -(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
        // get the location of the touch
        CGPoint pt = [[touches anyObject] locationInView:self];
        // puch the touch location (pt) onto our array of points
        [self.points addObject:[NSValue valueWithCGPoint:pt]];
        // update display by calling it's 'drawRect' method
        [self setNeedsDisplay]; 

    }
    @end

只需将此视图添加为主视图的子视图，例如波纹管...

首先在 .h 文件中添加类。

@class TouchView;

然后在.h文件中创建像波纹管这样的对象。

TouchView *viewScratch;

并在.m文件中添加此代码

 - (void)viewDidLoad
   {
     viewScratch = [[TouchView alloc]initWithFrame:CGRectMake(0, 0, 1024, 694)];// set frame which you want...
    [viewScratch clipsToBounds];
    [viewScratch drawPic:[UIImage imageNamed:@"yourImageName"]];
    [self.view addSubview:viewScratch];
   }