iOS瘋狂詳解之imageIO完成漸進加載圖片

1、常見漸進加載圖片模式

目前咱們看到的漸進加載主要有如下三種實現方式:

1) 依次從web上加載不一樣尺寸的圖片，從小到大。最開始先拉取一個小縮略圖作拉伸顯示，而後拉取中等規格的圖，拉取完畢直接覆蓋顯示，最後拉取原圖，拉取完成後顯示原圖。

2）直接從web上拉取最大的圖片，每接受一點兒數據就顯示一點兒圖片，這樣就會實現從上到下一點點刷新出來的效果。

3）結合第1種和第2種，先拉取一個縮略圖作拉伸顯示，而後採用第二種方法直接拉取原圖，這樣便可以實現漸進加載，也能夠節省幾回中間的網絡請求。

今天咱們要討論的是CGImageSource實現從web端漸進加載圖片，要達到這個目的咱們須要建立一個URLConnnection，而後實現代理，每次接收到數據時更新圖片便可。下面主要的實現源碼:

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// //  SvIncrementallyImage.m //  SvIncrementallyImage // //  Created by  maple on 6/27/13. //  Copyright (c) 2013 maple. All rights reserved. //   # import "SvIncrementallyImage.h" # import <imageio imageio.h= "" > # import <corefoundation corefoundation.h= "" >   @interface SvIncrementallyImage () {      NSURLRequest    *_request;      NSURLConnection *_conn;            CGImageSourceRef _incrementallyImgSource;            NSMutableData   *_recieveData;      long long       _expectedLeght;      bool            _isLoadFinished; }   @property (nonatomic, retain) UIImage *image; @property (nonatomic, retain) UIImage *thumbImage;   @end   @implementation SvIncrementallyImage   @synthesize imageURL = _imageURL; @synthesize image    = _image; @synthesize thumbImage = _thumbImage;   - (id)initWithURL:(NSURL *)imageURL {      self = [ super init];      if (self) {          _imageURL = [imageURL retain];                    _request = [[NSURLRequest alloc] initWithURL:_imageURL];          _conn    = [[NSURLConnection alloc] initWithRequest:_request delegate:self];                    _incrementallyImgSource = CGImageSourceCreateIncremental(NULL);                    _recieveData = [[NSMutableData alloc] init];          _isLoadFinished = false ;      }            return self; }   #pragma mark - #pragma mark NSURLConnectionDataDelegate   - ( void )connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {      _expectedLeght = response.expectedContentLength;      NSLog(@ "expected Length: %lld" , _expectedLeght);      //得到大文件的長度     NSString *mimeType = response.MIMEType;  NSLog(@"MIME TYPE %@", mimeType);     //得到文件的類型（mimetype=image/jpeg ）;      NSArray *arr = [mimeType componentsSeparatedByString:@"/"]; //判斷有沒有image  是否是image類型      if (arr.count < 1 || ![[arr objectAtIndex: 0 ] isEqual:@ "image" ]) {          NSLog(@ "not a image url" );          [connection cancel];          [_conn release]; _conn = nil;      } }   - ( void )connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {      NSLog(@ "Connection %@ error, error info: %@" , connection, error); }   - ( void )connectionDidFinishLoading:(NSURLConnection *)connection {      NSLog(@ "Connection Loading Finished!!!" );            // if download image data not complete, create final image      if (!_isLoadFinished) {          CGImageSourceUpdateData(_incrementallyImgSource, (CFDataRef)_recieveData, _isLoadFinished);          CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_incrementallyImgSource, 0 , NULL);          self.image = [UIImage imageWithCGImage:imageRef];          CGImageRelease(imageRef);      } }   - ( void )connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {      [_recieveData appendData:data];            _isLoadFinished = false ;      if (_expectedLeght == _recieveData.length) {          _isLoadFinished = true ;      }      //imageIO框架中方法的運用      CGImageSourceUpdateData(_incrementallyImgSource, (CFDataRef)_recieveData, _isLoadFinished);      CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_incrementallyImgSource, 0 , NULL);      self.image = [UIImage imageWithCGImage:imageRef];      CGImageRelease(imageRef); }   @end </corefoundation></imageio>