我有一个搜索方法,可以将搜索建议返回给用户界面。每次用户在搜索框中输入新字符时都会触发此方法。
我添加了一些取消代码来取消之前的搜索请求。这可行,但不是所有时间。
private CancellationTokenSource cancellationTokenSource;
private async Task UserSearch(string searchCriteria)
{
Debug.WriteLine("Searching for {0}....", searchCriteria);
try
{
var cts = new CancellationTokenSource();
this.Suggestions = await this.SearchAsync(searchCriteria, cts.Token);
}
catch (OperationCanceledException)
{
Debug.WriteLine("Search({0}) cancelled", searchCriteria);
}
}
private async Task<IList<string>> SearchAsync(string searchCriteria, CancellationToken cancelToken)
{
CancellationTokenSource previousCts = this.cancellationTokenSource;
CancellationTokenSource linkedCts = CancellationTokenSource.CreateLinkedTokenSource(cancelToken);
this.cancellationTokenSource = linkedCts;
// if previous task running cancel it
if (previousCts != null)
{
previousCts.Cancel();
}
linkedCts.Token.ThrowIfCancellationRequested();
List<string> results =
(await this.searchProvider.SearchAsync(searchCriteria, linkedCts.Token)).ToList();
Debug.WriteLine("Search({0}) returned {1} records", searchCriteria, results.Count);
linkedCts.Dispose();
this.cancellationTokenSource = null;
return results;
}
例如。我得到以下调试消息:
SearchTerm changing to: Di
Searching for Di....
SearchTerm changing to: Dia
Searching for Dia....
Search(Di) cancelled
SearchTerm changing to: Diap
Searching for Diap....
Search(Diap) returned 323 records
Search(Dia) returned 3230 records
正如您所看到的那样,第一个搜索被取消但第二个搜索没有被删除,并且在最后一次搜索后返回给用户的结果不正确。
如何确保以前的任务始终被取消?
答案 0 :(得分:1)
我认为你可能会使你的解决方案变得复杂一点。您需要做的就是查看是否存在尚未取消的现有操作并取消它。然后执行新搜索。未经测试,但我认为应该这样做。
private CancellationTokenSource cancellationTokenSource;
private async Task UserSearch(string searchCriteria)
{
Debug.WriteLine("Searching for {0}....", searchCriteria);
try
{
if(cancellationTokenSource != null &&
!cancellationTokenSource.IsCancellationRequested)
{
cancellationTokenSource.Cancel();
}
cancellationTokenSource = new CancellationTokenSource();
this.Suggestions = await this.searchProvider.SearchAsync(searchCriteria, linkedCts.Token);
Debug.WriteLine("Search({0}) returned {1} records", searchCriteria, results.Count);
}
catch (OperationCanceledException)
{
Debug.WriteLine("Search({0}) cancelled", searchCriteria);
}
}
答案 1 :(得分:0)
您为时太晚取消了以前的查询,请尽快查询(直接在收到用户输入后,而不是在下一个查询中)。
答案 2 :(得分:0)
我认为问题是对 this.cancellationTokenSource 的多线程访问。如果说线程2太晚取消了线程1( searchProvider.SearchAsync 已完成),则可以在赋值后清除this.cancellationTokenSource(即线程2执行 this.cancellationTokenSource = linkedCts; 和之后的线程1调用 this.cancellationTokenSource = null; )。这将有效地完全禁用线程2的取消
因此,你最好在下一个搜索开始之前取消一个搜索,就像@Ned Stoyanov的建议一样