1 圖片處理

1.1 編輯圖片的幾個方法

第一種

先用UIImage對象加載一張圖片

然後轉化成CGImageRef放到CGContext中去編輯

第二種

用CGImageCreate函數創建CGImageRef

然後把CGImageRef放到CGContext中去編輯

第三種

用CGImageCreateCopy 或者CGImageCreateCopyWithColorSpace函數拷貝

CGImageRefCGImageCreate (

size_t width, //圖片的寬度

size_t height, //圖片的高度

size_t bitsPerComponent, //圖片每個顏色的bits，比如rgb顏色空間，有可能是5 或者8 ==

size_t bitsPerPixel, //每一個像素佔用的buts，15 位24位 32位等等

size_t bytesPerRow, //每一行佔用多少bytes 注意是bytes不是bits 1byte ＝8bit

CGColorSpaceRef colorspace, //顏色空間，比如rgb

CGBitmapInfo bitmapInfo, //layout，像素中bit的佈局，是rgba還是 argb，＝＝

CGDataProviderRef provider, //數據源提供者，url或者內存＝＝

const CGFloat decode[], //一個解碼數組

bool shouldInterpolate, //抗鋸齒參數

CGColorRenderingIntent intent

//圖片渲染相關參數

);

1.2 示例代碼

CGImageRef CGImageCreate(size_t width, size_theight, size_tbitsPerComponent, size_t bitsPerPixel, size_tbytesPerRow, CGColorSpaceRef space, CGBitmapInfo bitmapInfo, CGDataProviderRefprovider, const CGFloat decode[], boolshouldInterpolate, CGColorRenderingIntent intent);

通過這個方法，我們可以創建出一個CGImageRef類型的對象，下面分別對參數進行解釋：

sizt_t是定義的一個可移植性的單位，在64位機器中爲8字節，32位位4字節。

width：圖片寬度像素

height：圖片高度像素

bitsPerComponent：每個顏色的比特數，例如在rgba-32模式下爲8

bitsPerPixel：每個像素的總比特數

bytesPerRow：每一行佔用的字節數，注意這裏的單位是字節

space：顏色空間模式，例如const CFStringRef kCGColorSpaceGenericRGB 這個函數可以返回一個顏色空間對象。

bitmapInfo：位圖像素佈局，枚舉如下：

typedef CF_OPTIONS(uint32_t, CGBitmapInfo) {

kCGBitmapAlphaInfoMask = 0x1F,

kCGBitmapFloatComponents = (1 << 8),

kCGBitmapByteOrderMask = 0x7000,

kCGBitmapByteOrderDefault = (0 << 12),

kCGBitmapByteOrder16Little = (1 << 12),

kCGBitmapByteOrder32Little = (2 << 12),

kCGBitmapByteOrder16Big = (3 << 12),

kCGBitmapByteOrder32Big = (4 << 12)

}

provider：數據源提供者

decode[]：解碼渲染數組

shouldInterpolate：是否抗鋸齒

intent：圖片相關參數

CGImageRef CGImageMaskCreate(size_t width, size_theight, size_t bitsPerComponent, size_t bitsPerPixel, size_tbytesPerRow, CGDataProviderRef provider, const CGFloat decode[], boolshouldInterpolate)

這個方法用於創建mask圖片圖層，可以設置其顯示部分與不顯示部分達到特殊的效果，參數意義同上。

CGImageRef CGImageCreateCopy(CGImageRefimage)

這個方法可以複製一個CGImageRef對象

CGImageRef CGImageCreateWithJPEGDataProvider(CGDataProviderRef source, const CGFloat decode[], boolshouldInterpolate, CGColorRenderingIntent intent)

通過JPEG數據源獲取圖像

CGImageRef CGImageCreateWithPNGDataProvider(CGDataProviderRefsource, const CGFloat decode[], boolshouldInterpolate, CGColorRenderingIntent intent)

通過PNG數據源獲取圖像

CGImageRef CGImageCreateWithImageInRect(CGImageRefimage, CGRectrect)

截取圖像的一個區域重繪圖像

CGImageRef CGImageCreateWithMask(CGImageRef image, CGImageRefmask)

截取mask圖像的某一區域重繪

CGImageRef CGImageCreateWithMaskingColors(CGImageRefimage, const CGFloatcomponents[])

通過顏色分量數組創建位圖

CGImageRef CGImageCreateCopyWithColorSpace(CGImageRefimage, CGColorSpaceRef space)

通過顏色空間模式複製位圖

CGImageRef CGImageRetain(CGImageRefimage)

引用+1

void CGImageRelease(CGImageRefimage)

引用-1

bool CGImageIsMask(CGImageRefimage)

返回是否爲Mask圖層

size_t CGImageGetWidth(CGImageRefimage)

獲取寬度像素

size_t CGImageGetHeight(CGImageRefimage)

獲取高度像素

下面這些方法分別獲取相應屬性

size_t CGImageGetBitsPerComponent(CGImageRefimage)

size_t CGImageGetBitsPerPixel(CGImageRefimage)

size_t CGImageGetBytesPerRow(CGImageRefimage)

CGColorSpaceRef CGImageGetColorSpace(CGImageRef image)CG_EXTERN CGImageAlphaInfo CGImageGetAlphaInfo(CGImageRefimage)

CGDataProviderRef CGImageGetDataProvider(CGImageRefimage)

const CGFloat *CGImageGetDecode(CGImageRefimage)

bool CGImageGetShouldInterpolate(CGImageRefimage)

CGColorRenderingIntent CGImageGetRenderingIntent(CGImageRefimage)

CGBitmapInfo CGImageGetBitmapInfo(CGImageRefimage)

1.3 PNG與JPEG優劣比較

存儲速度：JPG更快

壓縮比：JPG更大；

圖片質量：JPG更好

JPG不支持透明效果；

UIImageJPEGRepresentation方法在耗時上比較少而UIImagePNGRepresentation耗時操作時間比較長；

UIImageJPEGRepresentation函數需要兩個參數:圖片的引用和壓縮係數.而UIImagePNGRepresentation只需要圖片引用作爲參數.通過在實際使用過程中,比較發現: UIImagePNGRepresentation(UIImage* image) 要比UIImageJPEGRepresentation(UIImage* image, 1.0) 返回的圖片數據量大很多.譬如,同樣是讀取攝像頭拍攝的同樣景色的照片, UIImagePNGRepresentation()返回的數據量大小爲199K ,而 UIImageJPEGRepresentation(UIImage* image, 1.0)返回的數據量大小隻爲140KB,比前者少了50多KB.如果對圖片的清晰度要求不高,還可以通過設置 UIImageJPEGRepresentation函數的第二個參數,大幅度降低圖片數據量.譬如,剛纔拍攝的圖片, 通過調用UIImageJPEGRepresentation(UIImage* image, 1.0)讀取數據時,返回的數據大小爲140KB,但更改壓縮係數後,通過調用UIImageJPEGRepresentation(UIImage* image, 0.5)讀取數據時,返回的數據大小隻有11KB多,大大壓縮了圖片的數據量 ,而且從視角角度看,圖片的質量並沒有明顯的降低.因此,在讀取圖片數據內容時,建議優先使用UIImageJPEGRepresentation,並可根據自己的實際使用場景,設置壓縮係數,進一步降低圖片數據量大小.

1.4 圖片縮放

圖片縮放的三個函數

http://www.cnblogs.com/pengyingh/articles/2355052.html

程序中一個界面用到了好多張大圖，內存報警告了，所以做了一下圖片縮放，在網上找了別人寫的代碼

//把圖片做等比縮放，生成一個新圖片

- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize sourceImage:(UIImage*)sourceImage {

// UIGraphicsBeginImageContext(targetSize);

// [sourceImage drawInRect:CGRectMake(0,0, targetSize.width, targetSize.height)];

// UIImage* scaledImage =UIGraphicsGetImageFromCurrentImageContext();

// UIGraphicsEndImageContext();

// return scaledImage;

UIImage*newImage = nil;

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);

UIGraphicsBeginImageContext(targetSize);// this will crop

CGRect thumbnailRect = CGRectZero;

thumbnailRect.origin = thumbnailPoint;

thumbnailRect.size.width = scaledWidth;

thumbnailRect.size.height = scaledHeight;

[sourceImage drawInRect:thumbnailRect];

newImage =UIGraphicsGetImageFromCurrentImageContext();

if(newImage== nil)

NSLog(@"could not scale image");

//pop thecontext to get back to the default

UIGraphicsEndImageContext();

return newImage;

}

//把圖片按照新大小進行裁剪，生成一個新圖片

- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize image:(UIImage *)sourceImage

{

// UIImage*sourceImage = self;

UIImage*newImage = nil;

CGSizeimageSize = sourceImage.size;

CGFloat width= imageSize.width;

CGFloat height= imageSize.height;

CGFloattargetWidth = targetSize.width;

CGFloattargetHeight = 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;

// centerthe image

if (widthFactor > heightFactor)

{

thumbnailPoint.y = (targetHeight -scaledHeight) *0.5;

}

else

if(widthFactor < heightFactor)

{

thumbnailPoint.x =(targetWidth - scaledWidth) *0.5;

}

UIGraphicsBeginImageContext(targetSize);// this will crop

CGRect thumbnailRect = CGRectZero;

thumbnailRect.origin = thumbnailPoint;

thumbnailRect.size.width = scaledWidth;

thumbnailRect.size.height = scaledHeight;

[sourceImage drawInRect:thumbnailRect];

newImage =UIGraphicsGetImageFromCurrentImageContext();

if (newImage== nil)

NSLog(@"could not scale image");

//pop thecontext to get back to the default

UIGraphicsEndImageContext();

return newImage;

}

- (UIImage*)generatePhotoThumbnail:(UIImage *)image

{

// Create a thumbnail version of the image for the eventobject.

CGSize size =image.size;

CGSize croppedSize;

CGFloat ratio=64.0;//這個是設置轉換後圖片的尺寸大小

CGFloat offsetX =0.0;

CGFloat offsetY =0.0;

// check the size of the image, we want to make it

// a square with sides the size of the smallest dimension

if(size.width > size.height) {

offsetX = (size.height - size.width) /2;

croppedSize = CGSizeMake(size.height, size.height);

}else{

offsetY = (size.width - size.height) /2;

croppedSize = CGSizeMake(size.width, size.width);

}

// Crop the image before resize

CGRect clippedRect = CGRectMake(offsetX *-1, offsetY * -1, croppedSize.width, croppedSize.height);

//裁剪圖片

CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], clippedRect);

// Donecropping

// Resize the image

CGRect rect = CGRectMake(0.0,0.0,ratio, ratio);

UIGraphicsBeginImageContext(rect.size);

[[UIImage imageWithCGImage: imageRef] drawInRect: rect];

UIImage *thumbnail =UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

// DoneResizing

return thumbnail;

}

實際應用簡化

-(UIImage *)generatePhotoThumbnail:(UIImage *)image

{

CGRect rect=CGRectMake(0,0,60,78);

//裁剪圖片

CGImageRefimageRef=CGImageCreateWithImageInRect([image CGImage], CGRectMake(0,0,140,182));

UIGraphicsBeginImageContext(rect.size);

[[UIImage imageWithCGImage:imageRef]drawInRect:rect];

//如果不裁剪圖片可以直接畫

//[image drawInRect:CGRectMake(0, 0,theSize.width, theSize.height)];

UIImage*thumbnail=UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

returnthumbnail;

}

附：

UIImage類並沒有提供縮放圖片需要用到的API，是不是覺得很吃驚？沒關係，我們自己來添加一個。

定義縮放圖片的Category

// UIImage+Scale.h

@interfaceUIImage (scale)

-(UIImage*)scaleToSize:(CGSize)size;

@end

實現這個Category的定義

// UIImage+Scale.m

#import"UIImage+Scale.h"

@implementation UIImage (scale)

-(UIImage*)scaleToSize:(CGSize)size

{

// 創建一個bitmap的context

// 並把它設置成爲當前正在使用的context

UIGraphicsBeginImageContext(size);

// 繪製改變大小的圖片

[self drawInRect: CGRectMake(0,0, size.width, size.height)];

// 從當前context中創建一個改變大小後的圖片

UIImage* scaledImage =UIGraphicsGetImageFromCurrentImageContext();

// 使當前的context出堆棧

UIGraphicsEndImageContext();

// 返回新的改變大小後的圖片

return scaledImage;

}

@end

如何使用

// 創建圖片

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

// 更改圖片大小

UIImage *scaledImage=[image scaleToSize:CGSizeMake(25.0f,35.0f)]

1.5 參考鏈接

IOS-圖片操作集合

http://blog.csdn.net/ch_soft/article/details/7685753

UIImagePNGRepresentation存在緩慢問題

http://blog.sina.com.cn/s/blog_95a3991f010162ws.html

UIImage變爲NSData並進行壓縮

http://www.cnblogs.com/robinkey/archive/2013/01/21/2869930.html

UIImageJPEGRepresentation和UIImagePNGRepresentation

http://blog.csdn.net/mideveloper/article/details/11473627

png有透明通道，JPEG無

http://blog.163.com/chentong1115@126/blog/static/45314732200972323921819/

透明PNG圖片有黑邊的解決方法

http://www.minroad.com/?p=9

用UIImage和UIButton畫出的按鈕，使用透明的png圖片，爲什麼會出現白邊

http://segmentfault.com/q/1010000000095447

JPG、PNG和GIF圖片的基本原理及優化方法

http://www.mahaixiang.cn/Photoshop/400.html

JPEG原理詳細

http://blog.chinaunix.net/uid-27002868-id-3220554.html

IOS開發中圖片資源使用png還是jpg格式

http://www.cnblogs.com/wengzilin/p/3485298.html

(good)ios開發圖片格式的選擇:png和jpg

http://m.blog.csdn.net/blog/awaylin113/22712317

IOS開發之保存圖片到Documents目錄及PNG，JPEG格式相互轉換

http://blog.csdn.net/sanpintian/article/details/7418755

iOS過濾png圖片透明部分點擊事件

http://www.cocoachina.com/industry/20121127/5192.html

JPEG壓縮原理

http://blog.csdn.net/xfortius/article/details/8904012

png壓縮原理

http://blog.csdn.net/zykun/article/details/1825086

iOS開發，圖片使用png好還是jpg好？

http://www.cocoachina.com/bbs/read.php?tid=110115

2 繪製文本

2.1 NSMutableAttributedString繪製

CGRect textViewRect = CGRectMake(ICON_SPACE, _imageHeight + ICON_SPACE, _postContentTextView.frame.size.width, _labelSize);

NSMutableAttributedString *str = [[NSMutableAttributedString alloc] initWithString: vm.contentText];

[str addAttribute:NSForegroundColorAttributeName value: kContentTextColor range:NSMakeRange(0,[vm.contentText length])];

[str addAttribute: NSFontAttributeName value: kContentTextFont range:NSMakeRange(0,[vm.contentText length])];

[str addAttribute: NSBackgroundColorDocumentAttribute value: [UIColor whiteColor] range: NSMakeRange(0, [vm.contentText length])];

[str drawInRect: textViewRect];

2.2 參考資料

IOS開發（78）之繪製文本

http://www.2cto.com/kf/201305/212045.html

iOS界面上繪製不同字體顏色大小的字符串

http://blog.csdn.net/wsk_123_123/article/details/23277457

初探NSAttributedString和NSMutableAttributedString的使用-LiuWJ

http://www.tuicool.com/articles/Fvqia2

iOS字符屬性NSAttributedString描述

http://my.oschina.net/lanrenbar/blog/395909

NSAttributedString詳解

http://www.cnblogs.com/zhw511006/archive/2012/09/21/2696700.html

3 異步繪製

3.1 異步繪製示例

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

CGRect drawRect = _bgImageView.frame;

UIGraphicsBeginImageContextWithOptions(drawRect.size, YES, 0);

CGContextRef context = UIGraphicsGetCurrentContext();

if(!context) {

return;

}

[[UIColor whiteColor] set];

CGContextFillRect(context, drawRect);

CGRect imgRect = CGRectZero;

if ([vm.contentImgPath length] > 0) {

imgRect =CGRectMake(0, 0, BODY_HEIGTH, _imageHeight);

[vm.contentImage drawInRect: contentImageView.frame blendMode: kCGBlendModeNormal alpha:1];

}

CGRect textViewRect = CGRectZero;

if ([vm.contentText length] > 0) {

NSMutableAttributedString*str;

if (!isContentDisplayCompletly) {

if (vm.digestText) {

str = [[NSMutableAttributedString alloc] initWithString: vm.digestText attributes: contentTextView.typingAttributes];

}else

str = [[NSMutableAttributedString alloc] initWithString: vm.contentText attributes: contentTextView.typingAttributes];

}else

str = [[NSMutableAttributedString alloc] initWithString: vm.contentText attributes: contentTextView.typingAttributes];

[strdrawInRect: contentTextView.frame];

}

if (_subjectTitleHeight> 0) {

CGRect subjectIconFrame = CGRectMake(_subjectButton.frame.origin.x, _subjectButton.frame.origin.y, 16, 16);

UIImage*iconImg = [UIImage imageNamed:@"FlagIcon"];

subjectIconFrame.size = iconImg.size;

[iconImg drawInRect: subjectIconFrame blendMode: kCGBlendModeNormal alpha:1];

CGRect subjectTitleFrame = CGRectMake(subjectIconFrame.origin.x + subjectIconFrame.size.width, subjectIconFrame.origin.y, 100, _subjectTitleHeight);

[_subjectButton.titleLabel.attributedText drawInRect: subjectTitleFrame];

}

UIImage*temp = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

dispatch_async(dispatch_get_main_queue(),^{

_bgImageView.image = nil;

_bgImageView.image=temp;

[self setHidden:NO];

});

3.2 DrawRect之後注意用hitTest:withEvent:方法處理事件接收

//用戶觸摸時第一時間加載內容

- (UIView*)hitTest:(CGPoint)point withEvent:(UIEvent*)event{

UIView*result = [super hitTest: point withEvent: event];

CGPoint buttonPoint = [_subjectButton convertPoint: point fromView: self];

if ([_subjectButton pointInside:buttonPointwithEvent:event]){

return _subjectButton;

}

returnresult;

}

3.3 參考鏈接

[iOS Animation]-CALayer繪圖效率-異步繪製

http://my.oschina.net/u/2438875/blog/507545?fromerr=R4LnEaJ5

CGDataProviderCreateWithData對內存數據的釋放

http://www.taofengping.com/2012/11/04/cgdataprovidercreatewithdata_memory_release/#.VnJQ6jaitZF

IOS中使用像素位圖(CGImageRef)對圖片進行處理

http://my.oschina.net/u/2340880/blog/406437?p={{currentPage-1}}

4 Asyncdisplaykit

4.1 參考鏈接

Asyncdisplaykit指南（一）

http://www.th7.cn/Program/IOS/201410/302413.shtml

AsyncDisplayKit教程：達到60FPS的滾動幀率

http://www.cocoachina.com/swift/20141124/10298.html

http://asyncdisplaykit.org/guide/

AsyncDisplayKit入門指南

http://www.cocoachina.com/ios/20141020/9975.html

5 開發技巧

5.1 常見問題

5.1.1 CGBitmapContextCreateImage繪製後內存泄露導致內存告警

CGBitmapContextCreateImage繪製的圖片會造成內存無法釋放，應該換用CGDataProviderCreateWithCFData。

5.1.1.1 方案一：修改源代碼，入緩存前壓縮

http://my.oschina.net/u/1244672/blog/510379

SDWebImage有一個SDWebImageDownloaderOperation類來執行下載操作的。裏面有個下載完成的方法：

- (void)connectionDidFinishLoading:(NSURLConnection*)aConnection {

SDWebImageDownloaderCompletedBlock completionBlock = self.completedBlock;

@synchronized(self) {

CFRunLoopStop(CFRunLoopGetCurrent());

self.thread = nil;

self.connection= nil;

[[NSNotificationCenter defaultCenter] postNotificationName: SDWebImageDownloadStopNotificati onobject: nil];

}

if (![[NSURLCache sharedURLCache] cachedResponseForRequest:_request]) {

responseFromCached= NO;

}

if(completionBlock)

{

if(self.options & SDWebImageDownloaderIgnoreCachedResponse &&responseFromCached) {

completionBlock(nil, nil, nil, YES);

}

else {

UIImage *image= [UIImage sd_imageWithData: self.imageData];

NSString *key= [[SDWebImageManager sharedManager] cacheKeyForURL: self.request.URL];

image = [self scaledImageForKey: key image: image];

// Do notforce decoding animated GIFs

if (!image.images) {

image = [UIImage decodedImageWithImage: image];

}

if (CGSizeEqualToSize(image.size, CGSizeZero)) {

completionBlock(nil, nil, [NSError errorWithDomain:@"SDWebImageErrorDomain" code:0userInfo:@{NSLocalizedDescriptionKey : @"Downloaded image has 0pixels"}], YES);

}

else {

completionBlock(image, self.imageData, nil, YES);

}

self.completionBlock= nil;

[self done];

}

其中，UIImage*image = [UIImage sd_imageWithData:self.imageData];就是將data轉換成image。

再看看sd_imageWithData:這個方法：

+ (UIImage*)sd_imageWithData:(NSData *)data {

UIImage*image;

NSString*imageContentType = [NSData sd_contentTypeForImageData: data];

if ([imageContentType isEqualToString:@"image/gif"]) {

image =[UIImage sd_animatedGIFWithData: data];

}

#ifdefSD_WEBP

else if([imageContentType isEqualToString:@"image/webp"])

{

image =[UIImage sd_imageWithWebPData: data];

}

#endif

else {

image =[[UIImage alloc] initWithData: data];

UIImageOrientation orientation = [self sd_imageOrientationFromImageData: data];

if(orientation != UIImageOrientationUp) {

image =[UIImage imageWithCGImage: image.CGImage scale: image.scale orientation: orientation];

}

return image;

}

這個方法在UIImage+MultiFormat裏面，是UIImage的一個類別處理。這句話很重要image =[[UIImage alloc] initWithData: data]; SDWebImage把下載下來的data直接轉成image，然後沒做等比縮放直接存起來使用。所以，我們只需要在這邊做處理即可：

UIImage+MultiFormat添加一個方法：

+(UIImage*)compressImageWith:(UIImage *)image

{

float imageWidth = image.size.width;

float imageHeight = image.size.height;

float width =640;

float height =image.size.height/(image.size.width/width);

float widthScale = imageWidth /width;

float heightScale = imageHeight /height;

// 創建一個bitmap的context

// 並把它設置成爲當前正在使用的context

UIGraphicsBeginImageContext(CGSizeMake(width, height));

if (widthScale> heightScale) {

[image drawInRect: CGRectMake(0, 0, imageWidth /heightScale , height)];

}

else {

[image drawInRect: CGRectMake(0, 0, width , imageHeight /widthScale)];

}

// 從當前context中創建一個改變大小後的圖片

UIImage*newImage = UIGraphicsGetImageFromCurrentImageContext();

// 使當前的context出堆棧

UIGraphicsEndImageContext();

return newImage;

}

然後在：image =[[UIImage alloc] initWithData: data];下面調用以下：

if (data.length/1024 > 1024) {

image = [self compressImageWith: image];

}

當data大於1M的時候做壓縮處理。革命尚未成功，還需要一步處理。在SDWebImageDownloaderOperation的connectionDidFinishLoading方法裏面的：

UIImage *image= [UIImage sd_imageWithData: self.imageData];

//將等比壓縮過的image在賦在轉成data賦給self.imageData

NSData *data =UIImageJPEGRepresentation(image, 1);

self.imageData = [NSMutableData dataWithData: data];

5.1.1.2 方案二：設置全局緩存大小

http://www.myexception.cn/swift/2033029.html

1、首先在appdelegate方法didFinishLaunchingWithOptions

SDImageCache.sharedImageCache().maxCacheSize=1024*1024*8設置一下最大的緩存大小。

2、在appdelegate applicationDidReceiveMemoryWarning里加入

SDImageCache.sharedImageCache().clearMemory()

SDWebImageManager.sharedManager().cancelAll()

5.1.1.3 方案三：定時清理內存緩存

http://www.bubuko.com/infodetail-956863.html

經過嘗試，發現了一個最簡單的完美解決該問題的方法

在使用SDWebImage加載較多圖片造成內存警告時，定期調用

[[SDImageCache sharedImageCache] setValue:nilforKey:@"memCache"];

5.1.1.4 方案四（不推薦）：修復SD庫代碼，不做解壓，直接返回壓縮的原圖

5.1.1.5 方案五（推薦）：使用CGDataProviderRef進行圖形解壓重繪

iOS開發中界面展示大圖片時UIImage的性能有關問題

http://www.myexception.cn/operating-system/578931.html

#import "SDWebImageDecoder.h"

@implementationUIImage (ForceDecode)

+ (UIImage*)decodedImageWithImage:(UIImage*)image {

if (image.images) {

// Do not decode animated images

return image;

}

UIImage *decompressedImage;

@autoreleasepool{

//核心代碼，可以解決內存未釋放問題

NSData *data = UIImageJPEGRepresentation(image, 1);

CGDataProviderRef dataProvider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);

CGImageRef imageRef = CGImageCreateWithPNGDataProvider(dataProvider, NULL, NO, kCGRenderingIntentDefault);

// CGImageRef imageRef = image.CGImage;

CGSize imageSize = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));

CGRect imageRect = (CGRect){.origin = CGPointZero, .size=imageSize};

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);

int infoMask = (bitmapInfo & kCGBitmapAlphaInfoMask);

BOOL anyNonAlpha = (infoMask == kCGImageAlphaNone || infoMask == kCGImageAlphaNoneSkipFirst || infoMask ==kCGImageAlphaNoneSkipLast);

// CGBitmapContextCreate doesn't support kCGImageAlphaNone with RGB.

//https://developer.apple.com/library/mac/#qa/qa1037/_index.html

if (infoMask == kCGImageAlphaNone&& CGColorSpaceGetNumberOfComponents(colorSpace)

> 1) {

// Unset the old alpha info.

bitmapInfo &= ~kCGBitmapAlphaInfoMask;

// Set noneSkipFirst.

bitmapInfo |= kCGImageAlphaNoneSkipFirst;

}

// Some PNGs tell us they have alpha but only 3 components. Odd.

else if (!anyNonAlpha && CGColorSpaceGetNumberOfComponents(colorSpace)

== 3) {

// Unset the old alpha info.

bitmapInfo &= ~kCGBitmapAlphaInfoMask;

bitmapInfo |=kCGImageAlphaPremultipliedFirst;

}

// It calculates the bytes-per-row based on the bitsPerComponent and width arguments.

CGContextRef context = CGBitmapContextCreate(NULL,

imageSize.width,

imageSize.height,

CGImageGetBitsPerComponent(imageRef), 0, colorSpace, bitmapInfo);

CGColorSpaceRelease(colorSpace);

// If failed, return undecompressed image

if (!context) return image;

CGContextDrawImage(context, imageRect, imageRef);

CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);

CGContextRelease(context);

decompressedImage = [UIImage imageWithCGImage: decompressedImageRef scale: image.scale orientation: image.imageOrientation];

CGImageRelease(decompressedImageRef);

}

// CVPixelBufferRef pixelBuffer;

// CreateCGImageFromCVPixelBuffer(pixelBuffer,&decompressedImageRef);

// CGImage *cgImage =CGBitmapContextCreateImage(context);

// CFDataRef dataRef =CGDataProviderCopyData(CGImageGetDataProvider(cgImage));

// CGImageRelease(cgImage);

// image->imageRef = dataRef;

// image->image = CFDataGetBytePtr(dataRef);

return decompressedImage;

}

5.1.2 UIImage自定義繪製的四種方法

///方法中會自動做縮放處理

+(void) getBitmapImage: (UIImage *)image Size: (CGSize)imageSize WithCompletionBlock:(HJCallbackBlock)block

{

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

UIGraphicsBeginImageContextWithOptions(imageSize, YES, 0);

CGContextRef context = UIGraphicsGetCurrentContext();

if(!context) {

dispatch_async(dispatch_get_main_queue(), ^{

block(image);

});

}

CGRect rect = CGRectMake(0, 0, imageSize.width, imageSize.height);

//座標系統已經自動考慮了縮放因素，不需要額外處理

[image drawInRect: rect blendMode: kCGBlendModeNormal alpha:1];

UIImage *temp = UIGraphicsGetImageFromCurrentImageContext();

NSData *tempData = UIImageJPEGRepresentation(temp, 1);

UIGraphicsEndImageContext();

//設置SDWebImage庫的緩存

NSString *device = [HJUtility getCurDeviceModel];

if ([device rangeOfString:@"iPhone 4"].length > 0) {

if (tempData.length > 500000) {

tempData =UIImageJPEGRepresentation(temp, 0.4);

}

temp = [UIImage imageWithData: tempData];

}

dispatch_async(dispatch_get_main_queue(), ^{

if(block) {

block(temp);

}

});

//方案二，內存有釋放，掛機

// UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);

// CGContextRef context = UIGraphicsGetCurrentContext();

// CGRect rect = CGRectMake(0, 0, imageSize.width * [UIScreenmainScreen].scale, imageSize.height * [UIScreen mainScreen].scale);

// // draw alpha-mask

//// CGContextSetBlendMode(context, kCGBlendModeNormal);

// CGContextDrawImage(context, rect, image.CGImage);

// // draw tint color, preserving alpha values of original image

//// CGContextSetBlendMode(context, kCGBlendModeSourceIn);

// CGContextFillRect(context, rect);

// //Set the original greyscale template as the overlay of the new image

// UIImage *imgData = [self verticallyFlipImage:image];

// [imgData drawInRect:imageRect];

// UIImage *colouredImage = UIGraphicsGetImageFromCurrentImageContext();

// UIGraphicsEndImageContext();

// colouredImage = [self verticallyFlipImage:colouredImage];

// CGContextRelease(context);

// return colouredImage;

//方案三，CGBitmapContextCreate方案，內存沒釋放

// CGFloat targetWidth = imageSize.width * [UIScreen mainScreen].scale;

// CGFloat targetHeight = imageSize.height * [UIScreen mainScreen].scale;

// CGImageRef imageRef = [image CGImage];

// CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);

// CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);

// CGContextRef bitmapContext;

// bitmapContext = CGBitmapContextCreate(NULL, targetWidth,targetHeight,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef),colorSpaceInfo, bitmapInfo);

// CGContextDrawImage(bitmapContext, CGRectMake(0, 0, targetWidth,targetHeight), imageRef);

// CGImageRef imgref = CGBitmapContextCreateImage(bitmapContext);

// UIImage* newImage = [UIImage imageWithCGImage:imgref];

// CGColorSpaceRelease(colorSpaceInfo);

// CGContextRelease(bitmapContext);

// CGImageRelease(imgref);

// return newImage;

//方案四，CGBitmapContextCreate方案，但是採用CGDataProviderCreateWithCFData方案解決內存佔用問題

// NSData *data = UIImageJPEGRepresentation(image, 1);

// CGDataProviderRef dataProvider =CGDataProviderCreateWithCFData((__bridge CFDataRef)data);

// CGImageRef imageRef = CGImageCreateWithJPEGDataProvider(dataProvider,

// NULL, NO,

// kCGRenderingIntentDefault);

// CGFloat targetWidth = imageSize.width * [UIScreen mainScreen].scale;

// CGFloat targetHeight = imageSize.height * [UIScreen mainScreen].scale;

// // CGImageRef imageRef = [image CGImage];

// CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);

// CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);

// CGContextRef bitmapContext;

// bitmapContext = CGBitmapContextCreate(NULL, targetWidth,targetHeight,CGImageGetBitsPerComponent(imageRef),0, colorSpaceInfo,bitmapInfo);

// CGContextDrawImage(bitmapContext, CGRectMake(0, 0, targetWidth,targetHeight), imageRef);

// // If failed, return undecompressed image

// if (!bitmapContext) return image;

// CGImageRef imgref = CGBitmapContextCreateImage(bitmapContext);

// UIImage* newImage = [UIImage imageWithCGImage:imgref];//[UIImageimageWithCGImage:decompressedImageRef scale:image.scaleorientation:image.imageOrientation];

// CGColorSpaceRelease(colorSpaceInfo);

// CGContextRelease(bitmapContext);

// CGImageRelease(imgref);

// return newImage;

}

5.1.3 繪製時單元格底部出現高度不定的細微黑線

問題原因：

將Text做寬高計算時，高度值容易得出小數數值，而頁面繪製均是基於整數像素點繪製，對於小數點部分，系統會做捨去處理（即便有縮放），固留下高度不定的未繪製區域（爲黑色）。

解決方案：

將計算出來的高度值做向下取整處理即可。

CGRect labelFrame = [content boundingRectWithSize: size options: NSStringDrawingTruncatesLastVisibleLine | NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading attributes:_postContentTextView.typingAttributes context: nil];

labelSize = labelFrame.size;

labelSize.height = ceilf(labelSize.height);