我一定不能像我想的那样掌握异步的东西,因为这使我挠头了几个小时。
我要完成的是:
- 将UI切换到"获取数据..."
- 用异步调用获取数据
- 根据异步调用的最终结果
我在视图中的WPF按钮中有以下回调
private void Button_Click(object sender, RoutedEventArgs e)
{
GeneratorButton.IsEnabled = false;
ResultMsg.Visibility = Visibility.Visible; //default text of "Fetching data..."
string tickersString = Tickers.Text;
if (!string.IsNullOrEmpty(tickersString))
{
tickersString = tickersString.ToUpper();
string[] tickers = tickersString.Split(',', ' ');
var stockGeneratorTask = Task.Factory.StartNew<bool>(() => GetStockDataAndGenerateCSV(tickers).Result);
var allTasks = new Task[] { stockGeneratorTask };
var tasksHandler = Task.Factory.ContinueWhenAll(allTasks, completedTasks =>
{
return stockGeneratorTask.Result;
});
if (tasksHandler.Result)
{
ResultMsg.Foreground = Brushes.Green;
ResultMsg.Text = "Your report was successfully generated.";
}
else
{
ResultMsg.Text = "There was an error while generating your report. Please try again later.";
ResultMsg.Foreground = Brushes.Red;
}
}
GeneratorButton.IsEnabled = true;
}
我的期望在用户键入按钮后立即看到"获取数据..."的默认文本。据我了解,正在发生的事情是该程序直接执行了异步任务,而当它返回时,它显示了成功(或错误)消息,但是除非我注释,否则它会跳过"获取数据..."从stockgeneratask声明的宣言中删除代码(没有发生异步调用)。
现在,如果此可见性开关在触发异步任务之前发生了,那么在实际进行异步调用之前,我不应该看到此更改吗?为什么我只在回来后才看到它?
事件处理程序是允许async void
的一个例外。考虑将事件处理程序异步整个过程,而不要混合诸如.Result
之类的阻塞呼叫,这可能会导致僵局。假设GetStockDataAndGenerateCSV
返回Task<bool>
,则应等待它。
private async void Button_Click(object sender, RoutedEventArgs e) {
GeneratorButton.IsEnabled = false;
ResultMsg.Visibility = Visibility.Visible; //default text of "Fetching data..."
var tickersString = Tickers.Text;
if (!string.IsNullOrEmpty(tickersString)) {
tickersString = tickersString.ToUpper();
string[] tickers = tickersString.Split(',', ' ');
if (await GetStockDataAndGenerateCSV(tickers)) {
ResultMsg.Foreground = Brushes.Green;
ResultMsg.Text = "Your report was successfully generated.";
} else {
ResultMsg.Foreground = Brushes.Red;
ResultMsg.Text = "There was an error while generating your report. Please try again later.";
}
}
GeneratorButton.IsEnabled = true;
}
参考异步/等待 - 异步编程中的最佳实践