UIImageView和UIImage

1.UIImageView中的视图内容显示模式

UIImageView *imageV=[[UIImageViewalloc]init];

imageV.scaleToFill------默认缩放填充;

imageV.scaleAspectfit-------有留白;

imageV.AspectFill------自适应填充,视图会被裁剪;

2.UIImageView显示圆形图片

圆形图像

设置圆形图像的原理很简单，通过设置UIImageView的圆角属性即可。首先我们需要保证待设置的图片资源大小为方形的（稍后我们会提供图像裁剪方法）。方法一

//设置图像显示控件为圆形
- (void)changeToCirclePicture
{
//设置圆角半径为方形边长一半
[self.imageView.layer setCornerRadius:CGRectGetHeight([self.imageView bounds]) / 2];
[self.imageView.layer setMasksToBounds:YES];

//设置边框宽度和颜色
[self.imageView.layer setBorderWidth:10];
[self.imageView.layer setBorderColor:[[UIColor grayColor] CGColor]];
}

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方法一

UIImageView *imageView1 = [[UIImageViewalloc] initWithImage:[UIImageimageNamed:@"11.png"]];
imageView1.frame = CGRectMake(60,100, 100, 100);
imageView1.layer.masksToBounds =YES;
imageView1.layer.cornerRadius =50;
[self.view addSubview:imageView1];
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方法二:

UIImageView *imageView2 = [[UIImageViewalloc] initWithFrame:CGRectMake(60,250, 100,100)];
UIImage *image2 = [UIImageimageNamed:@"12.png"];
imageView2.image = [self circleImage:image2 withParam:0];//调用下面的方法
[self.view addSubview:imageView2];

-(UIImage*) circleImage:(UIImage*) image withParam:(CGFloat) inset {
UIGraphicsBeginImageContext(image.size);
CGContextRef context =UIGraphicsGetCurrentContext();
//圆的边框宽度为2，颜色为红色
CGContextSetLineWidth(context,2);
CGContextSetStrokeColorWithColor(context, [UIColorredColor].CGColor);
CGRect rect = CGRectMake(inset, inset, image.size.width - inset *2.0f,
image.size.height - inset *2.0f);
CGContextAddEllipseInRect(context, rect);
CGContextClip(context);
//在圆区域内画出image原图
[image drawInRect:rect];
CGContextAddEllipseInRect(context, rect);
CGContextStrokePath(context);
//生成新的image
UIImage *newimg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newimg;
}

3.图像裁剪成正方形显示

虽然我们这个demon中并没有用到图片的裁剪，但是很有可能实践项目中会涉及到图片裁剪成正方形。裁剪算法也很简单，以最短边边长为裁剪正方形的边长，在图像剧中的位置进行裁剪。

//截取居中的方形图像
- (UIImage *)cutPicture:(UIImage *)raw
{
CGSize origImageSize = raw.size;
CGRect newRect = CGRectMake(0, 0, SCREEN_WIDTH, SCREEN_WIDTH);

float ratio = MAX(newRect.size.width / origImageSize.width, newRect.size.height / origImageSize.height);

//开启透明位图上下文
UIGraphicsBeginImageContextWithOptions(newRect.size, NO, 0.0);
//创建圆角矩形的对象，这里设置圆角为0
UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:newRect cornerRadius:0.0];
//裁剪图形上下文
[path addClip];

//让图片在缩略图绘制范围内居中
CGRect projectRect;
projectRect.size.width = ratio * origImageSize.width;
projectRect.size.height = ratio * origImageSize.height;
projectRect.origin.x = (newRect.size.width - projectRect.size.width) / 2.0;
projectRect.origin.y = (newRect.size.height - projectRect.size.height) / 2.0;

//在上下文中绘制图片
[raw drawInRect:projectRect];

//从上下文获取图片，并复制给item
UIImage *smallImage = UIGraphicsGetImageFromCurrentImageContext();

//清理图形上下文
UIGraphicsEndImageContext();

return smallImage;
}

=+++++++++++++++++++++++++++++++++++++++++++++++
UIIMage
1.创建UIIMage

UIImage *img=[UIIMage imageWithCGImage:<#(nonnull CGImageRef)#>];//加载的时候,1个像素就是一个点;

UIImage *img=[UIImage imageWithCGImage:<#(nonnull CGImageRef)#> scale:<#(CGFloat)#> orientation:<#(UIImageOrientation)#>];//可以设置缩放比例

UIImage *img=[UIImage imageNamed:<#(nonnull NSString *)#>];//图片会常驻内存中,直接从内存读取

UIImage *img=[UIImage imageWithContentsOfFile:<#(nonnull NSString *)#>];//不做缓存,从bundle路径中加载.速度慢

UIImage *image=[btn bacgaroundImageForState:UIViewControllerShowDetailTargetDidChangeNotification];//btn是按钮,从按钮中获取图片

//将图片转换成二进制

NSData *data= UIImagePNGRepresentation(img);

2.图片拉伸

UIImage
*resizeImage=[img resizableImageWithCapsets:UIEdgeInsetsMake(self.view.bounds.size.width/2,self.view.bounds.size.width/2,self.view.bounds.size.width/2,self.view.bounds.size.width/2)
resizingmode:UIImageResizingModeStretch];//UIImageResizingModeTitle是平铺,iOS5.0后

UIImage *image=[img stretchableImageWithleftcapWidth:self.view.bounds.size.width*0.5 topcapheight:self.view.bounds.size.height*0.5]; //iOS5.0 前