在开发中我们常常需要向服务器发送请求来获得数据, 正常的流程是这样:
- 发送请求
- 网络正常, 将数据刷新到UI
- 无网络，没有数据, 视图空白
这样就会导致同一个URL请求多次，服务器返回的数据可能都是一样的，比如服务器上的某张图片，无论下载多少次，返回的数据都是一样的。这样的情况可能会导致一下问题:
- 重复获取数据，造成用户流量的浪费
- 请求响应速度可能很慢
- 服务器不必要的压力
- 没网络的情况下没有数据
- ...
所以为了解决上面的问题，我们一般会对数据进行缓存处理，给用户更好的用户体验，减轻服务器的压力，实现缓存后的步骤:
- 先判断是否有缓存数据，如果有先加载缓存数据
- 判断有没有网络
- 没网,结束.
- 有网，继续请求，刷新数据，将服务器的数据缓存到硬盘
在iOS中，苹果已经为我们提供了NSURLCache类来实现缓存
但是这里我并没有使用苹果提供的，而是第三方YYCache来实现对网络请求的缓存
使用AFNetworking进行网络请求管理
- 对GET请求进行缓存
#pragma mark - 发送 GET 请求
/**
* GET请求
*
* @param url url
* @param params 请求的参数字典
* @param cache 是否缓存
* @param successBlock 成功的回调
* @param failureBlock 失败的回调
* @param showHUD 是否加载进度指示器
*/
+ (NSURLSessionTask *)getRequestWithUrl:(NSString *)url
params:(NSDictionary *)params
cache:(BOOL)isCache
successBlock:(QCSuccessBlock)successBlock
failureBlock:(QCFailureBlock)failureBlock
showHUD:(BOOL)showHUD{
__block NSURLSessionTask *session = nil;
if (isCache) {
id responseObject = [QCNetworkCache getCacheResponseObjectWithRequestUrl:url params:params];
if (responseObject) {
int code = 0;
NSString *msg = nil;
if (responseObject) {
//这个字段取决于 服务器
code = [responseObject[@"rsCode"] intValue];
msg = responseObject[@"rsMsg"];
}
successBlock ? successBlock(responseObject, code, msg) : 0;
}
}
//没有网络直接返回
if (networkStatus == QCNetworkStatusNotReachable) {
failureBlock ? failureBlock(QC_ERROR) : 0;
return session;
}
if(showHUD) NSLog(@"加载中");
session = [_manager GET:url parameters:params progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"加载完成");
int code = 0;
NSString *msg = nil;
if (responseObject) {
//这个字段取决于 服务器
code = [responseObject[@"rsCode"] intValue];
msg = responseObject[@"rsMsg"];
}
successBlock ? successBlock(responseObject, code, msg) : 0;
//缓存数据
isCache ? [QCNetworkCache cacheResponseObject:responseObject requestUrl:url params:params] : 0;
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"加载完成");
failureBlock ? failureBlock(error) : 0;
}];
[session resume];
return session;
}
保存缓存具体实现
/**
* 对请求进行缓存
*
* @param responseObject 需要缓存的数据
* @param requestUrl 请求url
* @param params 参数
*/
+ (void)cacheResponseObject:(id)responseObject
requestUrl:(NSString *)requestUrl
params:(NSDictionary *)params{
assert(responseObject);
assert(requestUrl);
if (!params) params = @{};
NSString *originString = [NSString stringWithFormat:@"%@-%@",requestUrl,params];
NSString *hash = [self md5:originString];
[cache setObject:responseObject forKey:hash withBlock:^{
NSLog(@"成功 hash = %@", hash);
}];
}
获取已缓存的请求
/**
* 获取已缓存的请求
*
* @param requestUrl 请求地址
* @param params 参数
*
* @return 缓存的数据
*/
+ (id)getCacheResponseObjectWithRequestUrl:(NSString *)requestUrl
params:(NSDictionary *)params{
assert(requestUrl);
if (!params) params = @{};
NSString *originString = [NSString stringWithFormat:@"%@-%@",requestUrl,params];
NSString *hash = [self md5:originString];
id cacheData = [cache objectForKey:hash];
return cacheData;
}
- 对下载请求进行缓存
#pragma mark - 文件下载
/**
* 文件下载 (带缓存)
*
* @param url 下载文件接口地址
* @param progressBlock 下载进度
* @param successBlock 成功回调
* @param failBlock 下载回调
* @param showHUD 是否加载进度指示器
*
* @return 返回的对象可取消请求
*/
+ (NSURLSessionTask *)downloadWithUrl:(NSString *)url
progressBlock:(QCProgressBlock)progressBlock
successBlock:(QCDownloadSuccessBlock)successBlock
failureBlock:(QCFailureBlock)failureBlock
showHUD:(BOOL)showHUD{
__block NSURLSessionTask *session = nil;
NSString *type = nil;
NSArray *subStringArr = nil;
NSURL *fileUrl = [QCNetworkCache getDownloadDataFromCacheWithRequestUrl:url];
if (fileUrl) {
if (successBlock) successBlock(fileUrl);
return session;
}
//没有网络直接返回
if (networkStatus == QCNetworkStatusNotReachable) {
failureBlock ? failureBlock(QC_ERROR) : 0;
return session;
}
if(showHUD) NSLog(@"加载中");
if (url) {
subStringArr = [url componentsSeparatedByString:@"."];
if (subStringArr.count > 0) {
type = subStringArr[subStringArr.count - 1];
}
}
//响应内容序列化为二进制
_manager.responseSerializer = [AFHTTPResponseSerializer serializer];
session = [_manager GET:url parameters:nil progress:^(NSProgress * _Nonnull downloadProgress) {
progressBlock ? progressBlock((float)downloadProgress.completedUnitCount/(float)downloadProgress.totalUnitCount) : 0;
} success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"加载完成");
if (successBlock) {
NSData *data = (NSData *)responseObject;
[QCNetworkCache saveDownloadData:data requestUrl:url];
NSURL *downFileUrl = [QCNetworkCache getDownloadDataFromCacheWithRequestUrl:url];
successBlock(downFileUrl);
}
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"加载完成");
failureBlock ? failureBlock(error) : 0;
}];
[session resume];
return session;
}
对下载的数据进行缓存
/**
* 对下载的数据进行缓存
*
* @param data 下载的数据
* @param requestUrl 请求url
*/
+ (void)saveDownloadData:(NSData *)data
requestUrl:(NSString *)requestUrl {
assert(data);
assert(requestUrl);
NSString *fileName = nil;
NSString *type = nil;
NSArray *strArray = nil;
strArray = [requestUrl componentsSeparatedByString:@"."];
if (strArray.count > 0) {
type = strArray[strArray.count - 1];
}
if (type) {
fileName = [NSString stringWithFormat:@"%@.%@",[self md5:requestUrl],type];
}else {
fileName = [NSString stringWithFormat:@"%@",[self md5:requestUrl]];
}
NSString *directoryPath = nil;
directoryPath = [[NSUserDefaults standardUserDefaults] objectForKey:downloadDirKey];
if (!directoryPath) {
directoryPath = [[[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject] stringByAppendingPathComponent:@"QCNetworking"] stringByAppendingPathComponent:@"download"];
[[NSUserDefaults standardUserDefaults] setObject:directoryPath forKey:downloadDirKey];
[[NSUserDefaults standardUserDefaults] synchronize];
}
NSError *error = nil;
if (![[NSFileManager defaultManager] fileExistsAtPath:directoryPath isDirectory:nil]) {
[[NSFileManager defaultManager] createDirectoryAtPath:directoryPath withIntermediateDirectories:YES attributes:nil error:&error];
}
if (error) {
NSLog(@"创建目录错误: %@",error.localizedDescription);
return;
}
NSString *filePath = [directoryPath stringByAppendingPathComponent:fileName];
[[NSFileManager defaultManager] createFileAtPath:filePath contents:data attributes:nil];
}
获取已缓存的下载数据
/**
* 获取已缓存的下载数据
*
* @param requestUrl 请求url
*
* @return 缓存的url路径
*/
+ (NSURL *)getDownloadDataFromCacheWithRequestUrl:(NSString *)requestUrl {
assert(requestUrl);
NSData *data = nil;
NSString *fileName = nil;
NSString *type = nil;
NSArray *strArray = nil;
NSURL *fileUrl = nil;
strArray = [requestUrl componentsSeparatedByString:@"."];
if (strArray.count > 0) {
type = strArray[strArray.count - 1];
}
if (type) {
fileName = [NSString stringWithFormat:@"%@.%@",[self md5:requestUrl],type];
}else {
fileName = [NSString stringWithFormat:@"%@",[self md5:requestUrl]];
}
NSString *directoryPath = [[NSUserDefaults standardUserDefaults] objectForKey:downloadDirKey];
if (directoryPath){
NSString *filePath = [directoryPath stringByAppendingPathComponent:fileName];
data = [[NSFileManager defaultManager] contentsAtPath:filePath];
}
if (data) {
NSString *path = [directoryPath stringByAppendingPathComponent:fileName];
fileUrl = [NSURL fileURLWithPath:path];
}
return fileUrl;
}