iPhone; uisearchbar 异步请求，在发送新请求之前取消

Question

大家好我希望在我的应用程序中添加一个搜索栏，用户可以在其中搜索城市和国家/地区 - 结果来自在线 API。

因此，当用户开始输入四个以上字符时，系统会向在线 API 发送搜索请求，并获取国家/地区、城市信息。这里的问题是；当用户键入时，会进行调用，但之前的任何调用尚未结束 - 导致应用程序感觉缓慢......

重申

1. 用户输入，比如说“唱歌”
2. 发送请求，并检索其中包含 Sing 的所有城市
3. 但即使在检索列表之前，用户也会继续输入“Singa”
4. 应用程序会等待第一个请求的结果，甚至有时，结果是一些垃圾。

我希望你们明白我的意思，我只需要取消任何待处理的请求并发送一个新的请求。我怎样才能实现这个目标？

一种方法是仅在用户单击“搜索”时检索列表 - 但我希望它更具交互性。

谢谢

Answer 1

我在这个问题上取得了一些积极的进展......正如 rog 提到的，使用 NSURLCOnnection 在发送新请求之前实现了取消。我的代码如下

- (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText
{
    if([searchText length]<4) return;
    else{
        //[tableData removeAllObjects];// remove all data that belongs to previous search
        //make the call
        url=[NSString stringWithFormat:@"http://xml.customweather.com/xml?client=clinique_test&client_password=f@c3$toF&product=search&search=%@",searchBar.text];      
        NSURLRequest *request=[NSURLRequest requestWithURL:[NSURL URLWithString:url] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:5.0];
        NSLog(@"%@",url);
        if(connection!=nil){ //cancel if in process
            NSLog(@"connection cancelled");
            [connection cancel];
        }
        connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];   
        NSLog(@"Making request");


    }
}

- (void)connection:(NSURLConnection *)theConnection didReceiveData:(NSData *)incrementalData {
    if (data==nil) {
        data =
        [[NSMutableData alloc] initWithCapacity:2048];
    }
    [data appendData:incrementalData];


    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
}

- (void)connectionDidFinishLoading:(NSURLConnection*)theConnection {
    NSString *res=[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@",res);           
    [connection release];
    connection=nil; 
    [data release];
    data=nil;
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
    /* MY custom function goes here*/

    }   
}

这对我来说效果很好 - 示例控制台输出是

2010-11-29 15:46:52.535 searchBar1[2931:207] Making request
2010-11-29 15:46:52.678 searchBar1[2931:207] connection cancelled
2010-11-29 15:46:52.690 searchBar1[2931:207] Making request
2010-11-29 15:46:52.871 searchBar1[2931:207] connection cancelled
2010-11-29 15:46:52.876 searchBar1[2931:207] Making request
2010-11-29 15:46:53.063 searchBar1[2931:207] connection cancelled
2010-11-29 15:46:53.069 searchBar1[2931:207] Making request
2010-11-29 15:46:53.367 searchBar1[2931:207] connection cancelled
2010-11-29 15:46:53.372 searchBar1[2931:207] Making request
2010-11-29 15:46:53.529 searchBar1[2931:207] connection cancelled
2010-11-29 15:46:53.535 searchBar1[2931:207] Making request
2010-11-29 15:46:54.354 searchBar1[2931:207] <?xml version="1.0" encoding="UTF-8"?>
<cw_citylist size="1" search_type="city">
<city id="75281"  name="Singapore"  state=""  state_name=""  country="SN"  country_name="Singapore"  lat="1.28"  long="103.84"  population="2930200"  timezone="8"  timezone_code="SGT"  timezone_id="Asia/Singapore"  localtime="Mon, 29 Nov 2010 15:50:43 SGT"  region="Indonesia"  weather_id="75281" />
</cw_citylist>
2010-11-29 15:46:54.360 searchBar1[2931:207] Searching for ... city
2010-11-29 15:46:54.364 searchBar1[2931:207] Found in Singapore, Singapore
2010-11-29 15:46:54.368 searchBar1[2931:207] contacts error in num of row
2010-11-29 15:46:54.374 searchBar1[2931:207] Array value is Singapore,Singapore

如果您发现当我在搜索栏中输入字符时请求被取消。