修改文档

README.md

@@ -1,2 +1,81 @@
 # ASHWebURLProtocol
 iOS WebView缓存
+###首先继承 `NSURLProtocol`
+
+```
++(BOOL)canInitWithRequest:(NSURLRequest *)request
+{
+    
+    ///通过UA 来判断是否UIWebView发起的请求
+    NSString* UA = [request valueForHTTPHeaderField:@"User-Agent"];
+    if ([UA containsString:@" AppleWebKit/"] == NO) {
+        return NO;
+    }
+    
+    if ([request valueForHTTPHeaderField:kHTTPHeaderField]) {
+        return NO;
+    }
+    return YES;
+}
+```
+`NSString* UA = [request valueForHTTPHeaderField:@"User-Agent"];`
+中可以判断是否是`WebView`发出的请求。
+当判断是`WebView`的时候才进行处理。
+
+```
+- (void)startLoading
+{
+    
+    
+    NSString *cachesPath = [self cachePathForRequest:[self request]];
+    ASHCachedData *cache = [NSKeyedUnarchiver unarchiveObjectWithFile:cachesPath];
+    
+    //使用缓存。
+    if (cache) {
+        NSData *data = cache.data;
+        
+        [[self client] URLProtocol:self didReceiveResponse:cache.response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
+        [[self client] URLProtocol:self didLoadData:data];
+        [[self client] URLProtocolDidFinishLoading:self];
+        //        return;
+    }
+    
+    //重新请求。
+    NSMutableURLRequest *newRequest = [self.request mutableCopy];
+
+    [newRequest setValue:@"" forHTTPHeaderField:kHTTPHeaderField];
+    [newRequest setCachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData];
+    
+    self.connection = [NSURLConnection connectionWithRequest:newRequest
+                                                                delegate:self];
+    
+}
+```
+###上面是主要的代码，先使用了缓存，然后再去重新请求，这样就会刷新请求数据.
+
+
+```
+- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
+    [self.client URLProtocolDidFinishLoading:self];
+    
+    NSString *cachesPath = [self cachePathForRequest:[self request]];
+    
+    
+    
+    ASHCachedData *cache = [ASHCachedData new];
+    cache.data = [self data];
+    cache.response = [self response];
+    
+    [NSKeyedArchiver archiveRootObject:cache toFile:cachesPath];
+}
+```
+
+###
+最后一段就是对内容进行保存，当然也可以根据后缀把图片单独用`SDWebImage`保存，可以和原生代码里面的图片共用缓存。
+
+
+###最后还需要注册一下 在 `AppDelegate` 中
+
+```
+[NSURLProtocol  registerClass:[ASHWebNSURLProtocol class]];
+```