实现热门话题数据获取服务
知道了怎么解析数据后，我们现在将上面所有的实现封装在方法中。
在GetTrends方法中，使用了一些委托作为参数，以便我们的类可以异步工作。
l Action> onGetTrendsCompleted, 在热门主题数据准备处理时调用。
l Action
l Action onFinally, 总是被调用, 无论是否有错误发生.
因此方法的签名如下：
public static void GetTrends(Action<IEnumerable<Trend>>
onGetTrendsCompleted = null, Action<Exception> onError = null,
Action onFinally = null)
onGetTrendsCompleted = null, Action<Exception> onError = null,
Action onFinally = null)
接下来我们需要WebClient来请求服务器端，以获取json数据。
WebClient webClient = new WebClient();
// register on download complete event
webClient.OpenReadCompleted += delegate(object sender, OpenReadCompletedEventArgs e)
{
...
};
webClient.OpenReadAsync(new Uri(string.Format
(WhatTheTrendSearchQuery, WhatTheTrendApplicationKey)));
// register on download complete event
webClient.OpenReadCompleted += delegate(object sender, OpenReadCompletedEventArgs e)
{
...
};
webClient.OpenReadAsync(new Uri(string.Format
(WhatTheTrendSearchQuery, WhatTheTrendApplicationKey)));
这里的WhatTheTrendSearchQuery的定义如下：
private const string WhatTheTrendSearchQuery =
"http://api.whatthetrend.com/api/v2/trends.json?api_key={0}";
onGetTrendsCompleted, onError, onFinally的事件处理代码如下：
/// <summary>
/// Gets the trends.
/// </summary>
/// <param name="onGetTrendsCompleted">The on get trends completed.</param>
/// <param name="onError">The on error.</param>
public static void GetTrends(Action<IEnumerable<Trend>>
onGetTrendsCompleted = null, Action<Exception> onError = null,
Action onFinally = null)
{
WebClient webClient = new WebClient();
// register on download complete event
webClient.OpenReadCompleted +=
delegate(object sender, OpenReadCompletedEventArgs e)
{
try
{
// report error
if (e.Error != null)
{
if (onError != null)
{
onError(e.Error);
}
return;
}
// convert json result to model
Stream stream = e.Result;
DataContractJsonSerializer dataContractJsonSerializer =
new DataContractJsonSerializer(typeof(TrendsResults));
TrendsResults trendsResults =
(TrendsResults)dataContractJsonSerializer.ReadObject(stream);
// notify completed callback
if (onGetTrendsCompleted != null)
{
onGetTrendsCompleted(trendsResults.trends);
}
}
finally
{
// notify finally callback
if (onFinally != null)
{
onFinally();
}
}
};
webClient.OpenReadAsync(new Uri(string.Format
(WhatTheTrendSearchQuery, WhatTheTrendApplicationKey)));
}
/// Gets the trends.
/// </summary>
/// <param name="onGetTrendsCompleted">The on get trends completed.</param>
/// <param name="onError">The on error.</param>
public static void GetTrends(Action<IEnumerable<Trend>>
onGetTrendsCompleted = null, Action<Exception> onError = null,
Action onFinally = null)
{
WebClient webClient = new WebClient();
// register on download complete event
webClient.OpenReadCompleted +=
delegate(object sender, OpenReadCompletedEventArgs e)
{
try
{
// report error
if (e.Error != null)
{
if (onError != null)
{
onError(e.Error);
}
return;
}
// convert json result to model
Stream stream = e.Result;
DataContractJsonSerializer dataContractJsonSerializer =
new DataContractJsonSerializer(typeof(TrendsResults));
TrendsResults trendsResults =
(TrendsResults)dataContractJsonSerializer.ReadObject(stream);
// notify completed callback
if (onGetTrendsCompleted != null)
{
onGetTrendsCompleted(trendsResults.trends);
}
}
finally
{
// notify finally callback
if (onFinally != null)
{
onFinally();
}
}
};
webClient.OpenReadAsync(new Uri(string.Format
(WhatTheTrendSearchQuery, WhatTheTrendApplicationKey)));
}
使用热门话题服务
最后为了在页面上显示10大热门信息，我们可以在MainPage.xmal.cs中放入如下的代码，以便实现数据和列表控件的绑定。
private void Button_Click(object sender, RoutedEventArgs e)
{
TwitterService.GetTrends(
(items) => { listbox.ItemsSource = items; },
(exception) => { MessageBox.Show(exception.Message); },
null
);
}
{
TwitterService.GetTrends(
(items) => { listbox.ItemsSource = items; },
(exception) => { MessageBox.Show(exception.Message); },
null
);
}
