c# - 在 WPF 应用程序中正确实现任务

Question

我正在寻找一些关于掌握 WPF 中的 Task 的建议，并且想知道是否有人可以查看我的代码并指出我做错了什么？

基本上，应用程序从 UI 获取邮政编码，用于实例化 Task 服务，该服务将获取经度/纬度，可通过实例访问，以用于其他服务或 UI 本身。

我想我可能有一个竞争条件，我希望在 ResultTextBlock.Text 设置为零时纠正它，但是通过实例化我看到了这些值设置。

如有任何关于Task 实现和布线的建议，我们将不胜感激。

服务代码

class PostcodeService
{
    string _result;
    string _postcode;

    HttpResponseMessage _response;        
    RootObject rootObject;

    public double Latitude { get; private set; }
    public double Longitude { get; private set; }        

    public PostcodeService(string postcode)
    {
        this._postcode = postcode;
        rootObject = new RootObject();
    }

    public async Task<string> GetLongLatAsync()
    {        
        using (HttpClient client = new HttpClient())
        {
            client.BaseAddress = new Uri("https://api.postcodes.io/postcodes/" + this._postcode);
            client.DefaultRequestHeaders.Accept.Clear();
            client.DefaultRequestHeaders.Accept.Add(
                new MediaTypeWithQualityHeaderValue("application/json"));  

            try
            {
                _response = await client.GetAsync(client.BaseAddress);
                if(_response.IsSuccessStatusCode)
                {
                    //cast result into model and then set long/lat properties which can then be used in the UI
                    _result = await _response.Content.ReadAsStringAsync();                     

                    rootObject = JsonConvert.DeserializeObject<RootObject>(_result);
                    Longitude = Double.Parse(rootObject.result.longitude.ToString());
                    Latitude =  Double.Parse(rootObject.result.latitude.ToString());
                }                                      
            }
            catch(Exception ex)
            {
                ex.ToString();
            }
        }

        TaskCompletionSource<string> tc = new TaskCompletionSource<string>(_result);

        return tc.ToString();
    }
}

界面代码

private void PostcodeButton_Click(object sender, RoutedEventArgs e)
{
    _clearStatus();

    if (_validatePostcode())
    {
        Task T1 = Task.Factory.StartNew(async () =>
        {
            // get long lat from api
            _postcode = new PostcodeService(PostcodeTextBox.Text);
            await _postcode.GetLongLatAsync();
        });

        //Race condition?
        ResultTextBlock.Text = _postcode.Latitude.ToString();
    }
}

Answer 1

您的GetLongLatAsync() 方法应该返回一个字符串:

public async Task<string> GetLongLatAsync()
{
    using (HttpClient client = new HttpClient())
    {
        client.BaseAddress = new Uri("https://api.postcodes.io/postcodes/" + this._postcode);
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(
            new MediaTypeWithQualityHeaderValue("application/json"));

        _response = await client.GetAsync(client.BaseAddress);
        string result = null;
        if (_response.IsSuccessStatusCode)
        {
            //cast result into model and then set long/lat properties which can then be used in the UI
            result = await _response.Content.ReadAsStringAsync();

            rootObject = JsonConvert.DeserializeObject<RootObject>(_result);
            Longitude = Double.Parse(rootObject.result.longitude.ToString());
            Latitude = Double.Parse(rootObject.result.latitude.ToString());
        }
        return result;
    }
}

...您只需在 UI 中等待 GetLongLatAsync():

private async void PostcodeButton_Click(object sender, RoutedEventArgs e)
{
    _clearStatus();
    if (_validatePostcode())
    {
        // get long lat from api
        _postcode = new PostcodeService(PostcodeTextBox.Text);
        string result = await _postcode.GetLongLatAsync();
        ResultTextBlock.Text = result.ToString();
    }
}

您不需要使用 TaskCompletionSource 也不需要启动新的 Task 来调用异步方法。