IOS学习笔记（二）取图片

实现动态选取矩形区域内image的功能：

主要思路：因为要随着用户的矩形区域选择，动态显示图片，还要把选择的矩形区域用虚线标识出来，所以要用到重绘（drawRect），then，就需要定义一个UIView的子视图，重写drawRect方法。显示选择区域的部分，用touchBegan，touchMove，touchEnd方法实现。

MyImageView.h

@interface MyImageView : UIView
@property CGPoint startPoint;
@property CGRect rectangle;
@property(strong,nonatomic)NSMutableArray *lineArray;
@property(strong,nonatomic)UIImage *image;
//-(void)setBackgroundImage;
@end

MyImageView.m

@implementation MyImageView
@synthesize startPoint = _startPoint;
@synthesize rectangle = _rectangle;
@synthesize lineArray = _lineArray;
@synthesize image = _image;
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
//        UIImage *image = [UIImage imageNamed:@"iphone.jpg"];
//        //CGPoint drawPoint = CGPointMake(0, 0);
//        [image drawInRect:self.frame];
    }
    return self;
}

// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    //UIGraphicsBeginImageContext
    // Drawing code
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGFloat dashPhase = 5.0;//dash:破折号 phase:相位
    CGFloat dashPattern[10] = {10.0,10.0};//
    size_t dashCount = 2;//dashPattern中的数的个数
    CGContextSetLineDash(context, dashPhase, dashPattern, dashCount);
    //CGPoint drawPoint = CGPointMake(0, 0);
    CGContextAddRect(context, self.rectangle);
    CGContextSetRGBStrokeColor(context,0,0, 0, 0.5);
    CGContextSetLineWidth(context, 0.5);
    CGContextStrokePath(context);
    
    
    CGPoint drawPoint = self.frame.origin;
    [self.image drawAtPoint:drawPoint];
    CGContextStrokePath(context);
    
}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSMutableArray *pointArray = [[NSMutableArray alloc]init];
    UITouch *touch = [touches anyObject];
    self.startPoint = [touch locationInView:self];
    NSValue *pointValue = [NSValue valueWithCGPoint:self.startPoint];
    [pointArray addObject:pointValue];
    [self.lineArray addObject:pointArray];
    [pointArray release];
    
}
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
//    UIGraphicsBeginImageContext(self.rectangle.size);
//    UIGraphicsGetCurrentContext();
//    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
//    self.image = image;
    UIImage *image = [UIImage imageNamed:@"iphone.jpg"];
    CGImageRef sourceImageRef = [image CGImage];  
    CGImageRef newImageRef = CGImageCreateWithImageInRect(sourceImageRef, self.rectangle);  
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];  
    self.image = newImage;
    [self setNeedsDisplay];
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint endPoint = [touch locationInView:self];
    NSValue *pointValue = [NSValue valueWithCGPoint:endPoint];
    NSMutableArray *pointArray = [self.lineArray lastObject];
    [pointArray addObject:pointValue];
    float dx =  endPoint.x - self.startPoint.x;
    float dy = endPoint.y - self.startPoint.y;
    if(dx > 0 && dy > 0)
    {
        self.rectangle = CGRectMake(self.startPoint.x, self.startPoint.y, dx, dy);
        [self setNeedsDisplay];
    }
    
}
@end