UIImageView自适应图片大小

 窗口大小获取:

 CGRect screenBounds = [ [UIScreenmainScreen]bounds];//返回的是带有状态栏的Rect

 CGRect rect = [ [UIScreenmainScreen]applicationFrame];//不包含状态栏的Rect

 UIImageView：

 一 ：圆角以及自适应图片大小

  UIImage* image = [UIImage imageNamed:@"image.png"];

  UIImageView* imageView = [[[UIImageView alloc] initWithImage:image] autorelease];

  imageView.frame = CGRectMake(, , , );

 imageView.layer.cornerRadius = ;

  imageView.layer.masksToBounds = YES;

 //自适应图片宽高比例

 imageView1.contentMode = UIViewContentModeScaleAspectFit;

 二 图片自适应UIImageView

 - (UIImage *)rescaleImageToSize:(CGSize)size {

 CGRect rect = CGRectMake(0.0, 0.0, size.width, size.height);

 UIGraphicsBeginImageContext(rect.size);

 [self drawInRect:rect];  // scales image to rect

 UIImage *resImage = UIGraphicsGetImageFromCurrentImageContext();

 UIGraphicsEndImageContext();

 return resImage;

 }

 - (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize;   //图片缩放裁剪

 - (UIImage*)transformWidth:(CGFloat)width height:(CGFloat)height; //改变大小

 + (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2; //合并图片

 + (UIImage *)imageFromImage:(UIImage *)image inRect:(CGRect)rect; //裁剪部分图片

 + (void)imageSavedToPhotosAlbum:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo;  //保存图片到媒体库

 关于图片缩放的线程安全和非线程安全操作.

 非线程安全的操作只能在主线程中进行操作,对于大图片的处理肯定会消耗大量的时间,如下面的方法

 方法 ： 使用 UIKit

 + (UIImage*)imageWithImage :( UIImage*)image scaledToSize :(CGSize)newSize;
 {
 // Create a graphics image context
 UIGraphicsBeginImageContext(newSize);

 // Tell the old image to draw in this new context, with the desired
 // new size
 [image drawInRect:CGRectMake(,,newSize.width,newSize.height)];

 // Get the new image from the context
 UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();

 // End the context
 UIGraphicsEndImageContext();

 // Return the new image.
 return newImage;

 }

 此方法很简单， 但是，这种方法不是线程安全的情况下.

 方法 ： 使用 CoreGraphics

 + (UIImage*)imageWithImage :( UIImage*)sourceImage scaledToSize :(CGSize)newSize;
 {

 CGFloat targetWidth = targetSize.width;
 CGFloat targetHeight = targetSize.height;
 CGImageRef imageRef = [sourceImage CGImage];
 CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
 CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);
 if (bitmapInfo == kCGImageAlphaNone) {
 bitmapInfo = kCGImageAlphaNoneSkipLast;

 }

 CGContextRef bitmap;

 if (sourceImage.imageOrientation == UIImageOrientationUp ||sourceImage.imageOrientation == UIImageOrientationDown) {
 bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo)

 } else {

 bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
 }

 if (sourceImage.imageOrientation == UIImageOrientationLeft) {
 CGContextRotateCTM (bitmap, radians());
 CGContextTranslateCTM (bitmap, , -targetHeight);

 } else if (sourceImage.imageOrientation ==UIImageOrientationRight) {
 CGContextRotateCTM (bitmap, radians(-));
 CGContextTranslateCTM (bitmap, -targetWidth, );

 } else if (sourceImage.imageOrientation == UIImageOrientationUp) {

 // NOTHING

 } else if (sourceImage.imageOrientation == UIImageOrientationDown){

 CGContextTranslateCTM (bitmap, targetWidth, targetHeight);
 CGContextRotateCTM (bitmap, radians(-.));

 }

 CGContextDrawImage(bitmap, CGRectMake(, , targetWidth,targetHeight), imageRef);
 CGImageRef ref = CGBitmapContextCreateImage(bitmap);
 UIImage* newImage = [UIImage imageWithCGImage:ref];
 CGContextRelease(bitmap);
 CGImageRelease(ref);
 return newImage;
 }

 这种方法的好处是它是线程安全，加上它负责的 （使用正确的颜色空间和位图信息，处理图像方向） 的小东西，UIKit 版本不会。
 如何调整和保持长宽比 （如 AspectFill 选项）？
 它是非常类似于上述，方法，它看起来像这样：

 + (UIImage*)imageWithImage :( UIImage*)sourceImage scaledToSizeWithSameAspectRatio :( CGSize)targetSize;
 {
 CGSize imageSize = sourceImage.size;
 CGFloat width = imageSize.width;
 CGFloat height = imageSize.height;
 CGFloat targetWidth = targetSize.width;
 CGFloat targetHeight = targetSize.height;
 CGFloat scaleFactor = 0.0;
 CGFloat scaledWidth = targetWidth;
 CGFloat scaledHeight = targetHeight;
 CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
 if (CGSizeEqualToSize(imageSize, targetSize) == NO) {
 CGFloat widthFactor = targetWidth / width;
 CGFloat heightFactor = targetHeight / height;
 if (widthFactor > heightFactor) {
 scaleFactor = widthFactor; // scale to fit height
 }
 else {
 scaleFactor = heightFactor; // scale to fit width
 }
 scaledWidth  = width * scaleFactor;
 scaledHeight = height * scaleFactor;
 // center the image
 if (widthFactor > heightFactor) {
 thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
 }
 else if (widthFactor < heightFactor) {
 thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
 }
 }
 CGImageRef imageRef = [sourceImage CGImage];
 CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
 CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);
 if (bitmapInfo == kCGImageAlphaNone) {
 bitmapInfo = kCGImageAlphaNoneSkipLast;
 }
 CGContextRef bitmap;
 if (sourceImage.imageOrientation == UIImageOrientationUp ||sourceImage.imageOrientation == UIImageOrientationDown) {
 bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
 } else {
 bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
 }

 // In the right or left cases, we need to switch scaledWidth and scaledHeight,
 // and also the thumbnail point
 if (sourceImage.imageOrientation == UIImageOrientationLeft) {
 thumbnailPoint = CGPointMake(thumbnailPoint.y, thumbnailPoint.x);
 CGFloat oldScaledWidth = scaledWidth;
 scaledWidth = scaledHeight;
 scaledHeight = oldScaledWidth;
 CGContextRotateCTM (bitmap, radians());
 CGContextTranslateCTM (bitmap, , -targetHeight);
 } else if (sourceImage.imageOrientation ==UIImageOrientationRight) {
 thumbnailPoint = CGPointMake(thumbnailPoint.y, thumbnailPoint.x);
 CGFloat oldScaledWidth = scaledWidth;
 scaledWidth = scaledHeight;
 scaledHeight = oldScaledWidth;
 CGContextRotateCTM (bitmap, radians(-));
 CGContextTranslateCTM (bitmap, -targetWidth, );
 } else if (sourceImage.imageOrientation == UIImageOrientationUp) {

 // NOTHING

 } else if (sourceImage.imageOrientation == UIImageOrientationDown){
 CGContextTranslateCTM (bitmap, targetWidth, targetHeight);
 CGContextRotateCTM (bitmap, radians(-.));
 }

 CGContextDrawImage(bitmap, CGRectMake(thumbnailPoint.x,thumbnailPoint.y, scaledWidth, scaledHeight), imageRef);
 CGImageRef ref = CGBitmapContextCreateImage(bitmap);
 UIImage* newImage = [UIImage imageWithCGImage:ref];
 CGContextRelease(bitmap);
 CGImageRelease(ref);
 return newImage;
 }