最近做一个项目,需要用到UITableView异步加载图片的例子,看到网上有一个EGOImageView的很好的例子。
但是由于,EGOImageView的实现比较复杂,于是自己就动手做了一个AsynImageView,同样可以实现EGOImageView的效果。
而且自己写的代码比较清晰,容易理解,同样可以实现指定placehoderImage以及指定imageURL,来进行图片的异步加载。
同时,如果图片已经请求过,则不会再重复请求网络,会直接读取本地缓存文件。
效果如下:
具体实现思路如下:
AsynImageView.h的文件内容:
1. #import <UIKit/UIKit.h>
2.
3. @interface AsynImageView : UIImageView
4. {
5. NSURLConnection *connection;
6. NSMutableData *loadData;
7. }
8. //图片对应的缓存在沙河中的路径
9. @property (nonatomic, retain) NSString *fileName;
10.
11. //指定默认未加载时,显示的默认图片
12. @property (nonatomic, retain) UIImage *placeholderImage;
13. //请求网络图片的URL
14. @property (nonatomic, retain) NSString *imageURL;
15.
16. @end
AsynImageView.m中的文件内容:
1. #import "AsynImageView.h"
2. #import <QuartzCore/QuartzCore.h>
3.
4. @implementation AsynImageView
5.
6. @synthesize imageURL = _imageURL;
7. @synthesize placeholderImage = _placeholderImage;
8.
9. @synthesize fileName = _fileName;
10.
11. - (id)initWithFrame:(CGRect)frame
12. {
13. self = [super initWithFrame:frame];
14. if (self) {
15. // Initialization code
16.
17. self.layer.borderColor = [[UIColor whiteColor] CGColor];
18. self.layer.borderWidth = 2.0;
19. self.backgroundColor = [UIColor grayColor];
20.
21. }
22. return self;
23. }
24.
25. //重写placeholderImage的Setter方法
26. -(void)setPlaceholderImage:(UIImage *)placeholderImage
27. {
28. if(placeholderImage != _placeholderImage)
29. {
30. [_placeholderImage release];
31.
32. _placeholderImage = placeholderImage;
33. //指定默认图片
34. }
35. }
36.
37. //重写imageURL的Setter方法
38. -(void)setImageURL:(NSString *)imageURL
39. {
40. if(imageURL != _imageURL)
41. {
42. //指定默认图片
43. [_imageURL release];
44. _imageURL = [imageURL retain];
45. }
46.
47. if(self.imageURL)
48. {
49. //确定图片的缓存地址
50. NSArray *path=NSSearchPathForDirectoriesInDomains(NSDocumentationDirectory, NSUserDomainMask, YES);
51. NSString *docDir=[path objectAtIndex:0];
52. "AsynImage"];
53.
54. NSFileManager *fm = [NSFileManager defaultManager];
55. if(![fm fileExistsAtPath:tmpPath])
56. {
57. [fm createDirectoryAtPath:tmpPath withIntermediateDirectories:YES attributes:nil error:nil];
58. }
59. "/"];
60. "%@/%@", tmpPath, [lineArray objectAtIndex:[lineArray count] - 1]];
61.
62. //判断图片是否已经下载过,如果已经下载到本地缓存,则不用重新下载。如果没有,请求网络进行下载。
63. if(![[NSFileManager defaultManager] fileExistsAtPath:_fileName])
64. {
65. //下载图片,保存到本地缓存中
66. [self loadImage];
67. }
68. else
69. {
70. //本地缓存中已经存在,直接指定请求的网络图片
71. self.image = [UIImage imageWithContentsOfFile:_fileName];
72. }
73. }
74. }
75.
76. //网络请求图片,缓存到本地沙河中
77. -(void)loadImage
78. {
79. //对路径进行编码
80. try {
81. //请求图片的下载路径
82. //定义一个缓存cache
83. NSURLCache *urlCache = [NSURLCache sharedURLCache];
84. /*设置缓存大小为1M*/
85. [urlCache setMemoryCapacity:1*124*1024];
86.
87. //设子请求超时时间为30s
88. NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:self.imageURL] cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:60.0];
89.
90. //从请求中获取缓存输出
91. NSCachedURLResponse *response = [urlCache cachedResponseForRequest:request];
92. if(response != nil)
93. {
94. // NSLog(@"如果又缓存输出,从缓存中获取数据");
95. [request setCachePolicy:NSURLRequestReturnCacheDataDontLoad];
96. }
97.
98. /*创建NSURLConnection*/
99. if(!connection)
100. connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
101. //开启一个runloop,使它始终处于运行状态
102.
103. UIApplication *app = [UIApplication sharedApplication];
104. app.networkActivityIndicatorVisible = YES;
105.
106. [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
107.
108. }
109. catch (NSException *exception) {
110. // NSLog(@"没有相关资源或者网络异常");
111. }
112. @finally {
113. //.....
114. }
115. }
116.
117. #pragma mark - NSURLConnection Delegate Methods
118. //请求成功,且接收数据(每接收一次调用一次函数)
119. -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
120. {
121. if(loadData==nil)
122. {
123. loadData=[[NSMutableData alloc]initWithCapacity:2048];
124. }
125. [loadData appendData:data];
126. }
127.
128. -(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
129. {
130.
131. }
132.
133. -(NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse
134. {
135. return cachedResponse;
136. // NSLog(@"将缓存输出");
137. }
138.
139. -(NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)response
140. {
141. // NSLog(@"即将发送请求");
142. return request;
143. }
144. //下载完成,将文件保存到沙河里面
145. -(void)connectionDidFinishLoading:(NSURLConnection *)theConnection
146. {
147. UIApplication *app = [UIApplication sharedApplication];
148. app.networkActivityIndicatorVisible = NO;
149.
150. //图片已经成功下载到本地缓存,指定图片
151. if([loadData writeToFile:_fileName atomically:YES])
152. {
153. self.image = [UIImage imageWithContentsOfFile:_fileName];
154. }
155.
156. connection = nil;
157. loadData = nil;
158.
159. }
160. //网络连接错误或者请求成功但是加载数据异常
161. -(void)connection:(NSURLConnection *)theConnection didFailWithError:(NSError *)error
162. {
163. UIApplication *app = [UIApplication sharedApplication];
164. app.networkActivityIndicatorVisible = NO;
165.
166. //如果发生错误,则重新加载
167. connection = nil;
168. loadData = nil;
169. [self loadImage];
170. }
171.
172. -(void)dealloc
173. {
174. [_fileName release];
175. [loadData release];
176. [connection release];
177.
178. [_placeholderImage release];
179. [_imageURL release];
180.
181. [super dealloc];
182. }
183.
184. @end
上面的AsynImageView的.h和.m文件,就是所要实现的核心代码。如果想要调用AsynImageView,则只需执行如下代码即可:(需导入#import"AsynImageView.h")
1. asynImgView = [[AsynImageView alloc] initWithFrame:CGRectMake(0, 5, 200, 100)];
2. "place.png"];
3. "http://images.17173.com/2012/news/2012/10/10/lj1010sb10ds.jpg"];
4. [self.view addSubView:asynImgView];
下面是我实现的UITableView异步加载图片的程序链接,就是上面的效果图的程序完整代码,大家可以参考一下:
如有不恰当的地方,还望指点。
另外,图片的缓存可以定期进行清理,在此处没有写出清理代码,可以自行添加。