iPhone/iOS图片相关(读取、保存、绘制、其它相关)

一.读取图片

1.从资源(resource)读取

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UIImage* image=[UIImage imageNamed:@"1.jpg"];

2.从网络读取

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NSURL *url=[NSURL URLWithString:@"http://www.sinaimg.cn/qc/photo_auto/chezhan/2012/50/00/15/80046_950.jpg"];
UIImage *imgFromUrl =[[UIImage alloc]initWithData:[NSData dataWithContentsOfURL:url]];

3.从手机本地读取

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//读取本地图片非resource
NSString *aPath3=[NSString stringWithFormat:@"%@/Documents/%@.jpg",NSHomeDirectory(),@"test"];
UIImage *imgFromUrl3=[[UIImage alloc]initWithContentsOfFile:aPath3];
UIImageView* imageView3=[[UIImageView alloc]initWithImage:imgFromUrl3];

4.从现有的context中获得图像

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//add ImageIO.framework and #import <ImageIO/ImageIO.h>
CGImageSourceRef source = CGImageSourceCreateWithURL((CFURLRef)url, NULL);
CGImageRef img= CGImageSourceCreateImageAtIndex(source,0,NULL);
CGContextRef ctx=UIGraphicsGetCurrentContext();
CGContextSaveGState(ctx);
//transformCTM的2种方式
//CGContextConcatCTM(ctx, CGAffineTransformMakeScale(.2, -0.2));
//CGContextScaleCTM(ctx,1,-1);
//注意坐标要反下,用ctx来作为图片源
CGImageRef capture=CGBitmapContextCreateImage(ctx);
CGContextDrawImage(ctx, CGRectMake(160, 0, 160, 230), [image CGImage]);
CGContextDrawImage(ctx, CGRectMake(160, 230, 160, 230), img);
CGImageRef capture2=CGBitmapContextCreateImage(ctx);

5.用Quartz的CGImageSourceRef来读取图片

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CGImageSourceRef source = CGImageSourceCreateWithURL((CFURLRef)url, NULL);
CGImageRef img= CGImageSourceCreateImageAtIndex(source,0,NULL);

二.保存图片

1.转换成NSData来保存图片（imgFromUrl是UIImage）

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//保存图片 2种获取路径都可以
//NSArray*paths=NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
//NSString*documentsDirectory=[paths objectAtIndex:0];
//NSString*aPath=[documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.jpg",@"test"]];
"%@/Documents/%@.jpg",NSHomeDirectory(),@"test"];
NSData *imgData = UIImageJPEGRepresentation(imgFromUrl,0);
[imgData writeToFile:aPath atomically:YES];

2.用Quartz的CGImageDestinationRef来输出图片，这个方式不常见，所以不做介绍，详细可以看apple文档Quartz 2D Programming Guide

三.绘制图(draw|painting)

1.UIImageView方式加入到UIView层

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UIImageView* imageView=[[UIImageView alloc]initWithImage:image];
imageView.frame=CGRectMake(0, 0, 320, 480);
[self addSubview:imageView];
[imageView release];

2.[img drawAtPoint]系列方法

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[image4 drawAtPoint:CGPointMake(100, 0)];

3.CGContextDrawImage

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CGContextDrawImage(ctx, CGRectMake(160, 0, 160, 230), [image CGImage]);

4.CGLayer
这个是apple推荐的一种offscreen的绘制方法，相比bitmapContext更好，因为它似乎会利用iphone硬件(drawing-card)加速

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CGLayerRef cg=CGLayerCreateWithContext(ctx, CGSizeMake(320, 480), NULL);
//需要将CGLayerContext来作为缓存context，这个是必须的
CGContextRef layerContext=CGLayerGetContext(cg);
CGContextDrawImage(layerContext, CGRectMake(160, 230, 160, 230), img);
CGContextDrawLayerAtPoint(ctx, CGPointMake(0, 0), cg);

5.CALayer的contents

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UIImage* image=[UIImage imageNamed:@"1.jpg"];
CALayer *ly=[CALayer layer];
ly.frame=CGRectMake(0, 0, 320, 460);
ly.contents=[image CGImage];
[self.layer addSublayer:ly];

四.其它

1.CGImage和UIImage互换
这样就可以随时切换UIKit和Quartz之间类型，并且选择您熟悉的方式来处理图片.
CGImage cgImage=[uiImage CGImage];
UIImage* uiImage=[UIImage imageWithCGImage:cgImage];

2.UIImage resizableImageWithCapInsets的问题
假设一张44x29的图片，同样的Insets=UIEdgeInsetsMake(10,10,10,10)在@2x情况和非@2x情况下，表现会有不同，非@2x是OK正常的，但是如果同样尺寸的图片变成@2x,则导致在切换过渡的时候会很卡，应该是在不同的重绘导致的，表面原因是因为Insets设置的是点，在@2x情况下拉伸，其实拉升的像素是上面20，下面也是20，但是图片其实只有29，所以导致不正确，只要将insets设置成=UIEdgeInsetsMake(5,10,5,10)就正常了，所以以后要注意了。

3.动画图片使用注意

animationImage 设置完毕以后要startAnimation.不会自动启动动画图片。

此外在读取大量动画图片的时候不太适合用这个方法，因为一下子那么多图片容易爆掉。可以用这个方法替代，具体我也没试，方法就是手动切换图片，并非直接使用系统方法而已。

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imgV=[[UIImageView alloc]initWithFrame:CGRectMake(40, 40, 128, 128)];
[self.window addSubview:imgV];
[self performSelectorInBackground:@selector(playAnim)withObject:nil];

[imgV release];
-(void)playAnim{
for (int i=0;i<101;){
usleep(100000);
UIImage *image=[[UIImage alloc]initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:[NSString stringWithFormat:@"%d",i+1 ] ofType:@"tiff"]];
[self performSelectorOnMainThread:@selector(changeImage:) withObject:image waitUntilDone:YES];
i++;

}
}
-(void)changeImage:(UIImage*)image{
imgV.image=image;
}

相关帖子：http://www.cocoachina.com/bbs/read.php?tid=110154

4.UIControl设置UIImage

问题描述主要是有一个很小的叉按钮，需要响应很大的点击区域，这个其实很简单，代码如下：

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UIImage *bg=[UIImage imageNamed:@"heizi1.jpg"];
//图片大于点及区域，缩小下就行
bg=[self scaleImage:bg ToSize:(CGSize){100,100}];
UIButton* button = [[UIButton alloc]initWithFrame:CGRectMake(0, 0, 200, 200)];
//图片大于button，则会被拉伸，如果小于button则居中显示
[button setImage:bg forState:UIControlStateNormal];

此外多说一句，这个icon图片如果要准备2套图,缩放毕竟消耗效率

缩放图片代码

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-(UIImage *)scaleImage:(UIImage *)img ToSize:(CGSize)itemSize{

UIImage *i;
// CGSize itemSize=CGSizeMake(30, 30);
UIGraphicsBeginImageContext(itemSize);
CGRect imageRect=CGRectMake(0, 0, itemSize.width, itemSize.height);
[img drawInRect:imageRect];
i=UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return i;

从view截图出来

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#import <QuartzCore/QuartzCore.h>

-(UIImage *)getImageFromView:(UIView *)orgView{
UIGraphicsBeginImageContext(orgView.bounds.size);
[orgView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return image;
}

从网络下载图片，保存，并用 UIImageView 从保存中显示

//从网络下载图片
-(UIImage *) getImageFromURL:(NSString *)fileURL {
NSLog(@"执行图片下载函数");
UIImage * result;

NSData * data = [NSData dataWithContentsOfURL:[NSURL URLWithString:fileURL]];
result = [UIImage imageWithData:data];

return result;
}

//将所下载的图片保存到本地
-(void) saveImage:(UIImage *)image withFileName:(NSString *)imageName ofType:(NSString *)extension inDirectory:(NSString *)directoryPath {
if ([[extension lowercaseString] isEqualToString:@"png"]) {
[UIImagePNGRepresentation(image) writeToFile:[directoryPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.%@", imageName, @"png"]] options:NSAtomicWrite error:nil];
} else if ([[extension lowercaseString] isEqualToString:@"jpg"] || [[extension lowercaseString] isEqualToString:@"jpeg"]) {
[UIImageJPEGRepresentation(image, 1.0) writeToFile:[directoryPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.%@", imageName, @"jpg"]] options:NSAtomicWrite error:nil];
} else {
//ALog(@"Image Save Failed\\nExtension: (%@) is not recognized, use (PNG/JPG)", extension);
NSLog(@"文件后缀不认识");
}
}

//读取本地保存的图片
-(UIImage *) loadImage:(NSString *)fileName ofType:(NSString *)extension inDirectory:(NSString *)directoryPath {
UIImage * result = [UIImage imageWithContentsOfFile:[NSString stringWithFormat:@"%@/%@.%@", directoryPath, fileName, extension]];

return result;
}

//从网络下载图片，保存，并用 UIImageView 从保存中显示
NSString * documentsDirectoryPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSLog(@"保存路径:%@",documentsDirectoryPath);
//Get Image From URL
UIImage * imageFromURL = [self getImageFromURL:@"http://file.duteba.com/phone/2009/04/5/ftGxL8kcUL.jpg"];

//Save Image to Directory
[self saveImage:imageFromURL withFileName:@"MyImage" ofType:@"jpg" inDirectory:documentsDirectoryPath];

//Load Image From Directory
UIImage * imageFromWeb = [self loadImage:@"MyImage" ofType:@"jpg" inDirectory:documentsDirectoryPath];
[img setImage:imageFromWeb];

//取得目录下所有文件名
NSArray *file = [[[NSFileManager alloc] init] subpathsAtPath:documentsDirectoryPath];
//NSLog(@"%d",[file count]);
NSLog(@"%@",file);
//该片段来自于http://outofmemory.cn