总结:我想在构造函数中调用异步方法。这可能吗?
详细信息:我有一个名为getwritings()的方法，用于解析JSON数据。如果我只是在异步方法中调用getwritings()并将await放在它的左边，那么一切都可以正常工作。然而，当我在我的页面中创建一个LongListView并试图填充它时，我发现getWritings()令人惊讶地返回null, LongListView为空。
为了解决这个问题，我尝试将getWritings()的返回类型更改为Task<List<Writing>>，然后通过getWritings(). result在构造函数中检索结果。然而，这样做最终会阻塞UI线程。
public partial class Page2 : PhoneApplicationPage
{
List<Writing> writings;
public Page2()
{
InitializeComponent();
getWritings();
}
private async void getWritings()
{
string jsonData = await JsonDataManager.GetJsonAsync("1");
JObject obj = JObject.Parse(jsonData);
JArray array = (JArray)obj["posts"];
for (int i = 0; i < array.Count; i++)
{
Writing writing = new Writing();
writing.content = JsonDataManager.JsonParse(array, i, "content");
writing.date = JsonDataManager.JsonParse(array, i, "date");
writing.image = JsonDataManager.JsonParse(array, i, "url");
writing.summary = JsonDataManager.JsonParse(array, i, "excerpt");
writing.title = JsonDataManager.JsonParse(array, i, "title");
writings.Add(writing);
}
myLongList.ItemsSource = writings;
}
}
有点晚了，但我认为很多人都在努力解决这个问题……
我也一直在找这个。为了让你的方法/动作运行异步而不等待或阻塞线程，你需要通过SynchronizationContext来排队，所以我想出了这个解决方案:
我为它做了一个辅助类。
public static class ASyncHelper
{
public static void RunAsync(Func<Task> func)
{
var context = SynchronizationContext.Current;
// you don't want to run it on a threadpool. So if it is null,
// you're not on a UI thread.
if (context == null)
throw new NotSupportedException(
"The current thread doesn't have a SynchronizationContext");
// post an Action as async and await the function in it.
context.Post(new SendOrPostCallback(async state => await func()), null);
}
public static void RunAsync<T>(Func<T, Task> func, T argument)
{
var context = SynchronizationContext.Current;
// you don't want to run it on a threadpool. So if it is null,
// you're not on a UI thread.
if (context == null)
throw new NotSupportedException(
"The current thread doesn't have a SynchronizationContext");
// post an Action as async and await the function in it.
context.Post(new SendOrPostCallback(async state => await func((T)state)), argument);
}
}
使用/例子:
public partial class Form1 : Form
{
private async Task Initialize()
{
// replace code here...
await Task.Delay(1000);
}
private async Task Run(string myString)
{
// replace code here...
await Task.Delay(1000);
}
public Form1()
{
InitializeComponent();
// you don't have to await nothing.. (the thread must be running)
ASyncHelper.RunAsync(Initialize);
ASyncHelper.RunAsync(Run, "test");
// In your case
ASyncHelper.RunAsync(getWritings);
}
}
这适用于Windows。表单和WPF
布莱恩·拉古纳斯展示了一个我非常喜欢的解决方案。更多信息，他的youtube视频
解决方案:
添加一个TaskExtensions方法
public static class TaskExtensions
{
public static async void Await(this Task task, Action completedCallback = null ,Action<Exception> errorCallBack = null )
{
try
{
await task;
completedCallback?.Invoke();
}
catch (Exception e)
{
errorCallBack?.Invoke(e);
}
}
}
用法:
public class MyClass
{
public MyClass()
{
DoSomething().Await();
// DoSomething().Await(Completed, HandleError);
}
async Task DoSomething()
{
await Task.Delay(3000);
//Some works here
//throw new Exception("Thrown in task");
}
private void Completed()
{
//some thing;
}
private void HandleError(Exception ex)
{
//handle error
}
}
