iOS疯狂详解之imageIO完成渐进加载图片
一、常见渐进加载图片模式
目前我们看到的渐进加载主要有以下三种实现方式:
1) 依次从web上加载不同尺寸的图片，从小到大。最开始先拉取一个小缩略图做拉伸显示，然后拉取中等规格的图，拉取完毕直接覆盖显示，最后拉取原图，拉取完成后显示原图。
2）直接从web上拉取最大的图片，每接受一点儿数据就显示一点儿图片，这样就会实现从上到下一点点刷新出来的效果。
3）结合第1种和第2种，先拉取一个缩略图做拉伸显示，然后采用第二种方法直接拉取原图，这样即可以实现渐进加载，也可以节省几次中间的网络请求。
今天我们要讨论的是CGImageSource实现从web端渐进加载图片，要达到这个目的我们需要创建一个URLConnnection，然后实现代理，每次接收到数据时更新图片即可。下面主要的实现源码:
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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);
//获得大文件的长度
//获得文件的类型（mimetype=image/jpeg
）;
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框架中方法的运用
CGImageSourceUpdateData(_incrementallyImgSource, (CFDataRef)_recieveData, _isLoadFinished);
CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_incrementallyImgSource,
0
, NULL);
self.image = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
}
@end
</corefoundation></imageio>
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