iOS

已知：iOS客户端，在某个界面，连网时，需向后台请求数据，断网时，读取本地数据

问题：数据量大时，如何处理这么庞大的数据？

解决方法：先读取本地数据，再从线上请求数据，与本地数据比较，更新本地数据，再次从读取本地数据。

    [self loadFromDb];
    if (![[Helper isExistenceNetwork] isEqualToString:@"NotReachable"]) {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            [self loadFromService];
        });
    }

#pragma mark - 读取数据库

- (void)loadFromDb
{
    FMDatabase *db = [FMDatabase databaseWithPath:dbPath];
    if (![db open]) {
        NSLog(@"Could not open db.");
        return;
    }
    
    FMResultSet *blogListResult;

    blogListResult = [db executeQueryWithFormat:@"select语句];

    blogsData = [[NSMutableDictionary alloc] init];
    oldListSource = [[NSMutableArray alloc] init];
    
    while ([blogListResult next]) {
        NSMutableDictionary *blogsDic = [[NSMutableDictionary alloc] init];
    
       // 组装数据

        [blogsDic setObject:STATUS_DELETE forKey:@"status"];
        NSString *key =[NSString stringWithFormat:@"%@", [blogsDic objectForKey:@"id"]];
        [blogsData setObject:blogsDic forKey:key];
        [blogsListSource addObject:blogsDic];
        [oldListSource addObject:blogsDic];
    }
    
    [db close];
    [self reloadSource];
}

- (void)requestFinished:(ASIHTTPRequest *)request
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSDictionary *result = [[[NSString alloc] initWithData:[request responseData] encoding:NSUTF8StringEncoding] objectFromJSONString];
        NSArray *blogListAry = [result objectForKey:@"blogList"];

        BOOL isChanged = NO;
        FMDatabase *db = [FMDatabase databaseWithPath:dbPath];
        if (![db open]) {
            NSLog(@"Could not open db.");
            return;
        }
        
        if ([blogListAry count] != [oldListSource count]) {
            isChanged = YES;
        }
        
        for (int i = 0; i < [blogListAry count]; i++) {
            NSDictionary *blogs = [blogListAry objectAtIndex:i];
            if ([blogsData objectForKey:[NSString stringWithFormat:@"%@", [blogs objectForKey:@"id"]]]) {
                NSMutableDictionary *oldSpace = [blogsData objectForKey:[NSString stringWithFormat:@"%@", [blogs objectForKey:@"id"]]];
                //更新本地数据库
                isChanged = YES;
　　　　　　　　　　//改变oldSpace中key的值也就相当于改变了oldListSource中key的值
                [oldSpace setObject:STATUS_NORMAL forKey:@"status"];
            }else{
                //插入本地数据库
                isChanged = YES;
            }
        }
        
        if (isChanged) {
            for (int i = 0; i < [oldListSource count]; i++) {
                NSMutableDictionary *oSpace = [oldListSource objectAtIndex:i];
                if ([[oSpace objectForKey:@"status"] isEqualToString:STATUS_DELETE]) {
　　　　　　　　　　　　//删除数据库多余的数据
                }
            }
            dispatch_async(dispatch_get_main_queue(), ^{
                [self loadFromDb];
            });
        }
    });
}

OK，第一篇博客写完了。