c# – 如何使用约定使用Caliburn.Micro操作实现延迟

我有时需要延迟绑定执行(想想一个调用服务器的搜索框,你只希望它只在用户暂停一秒而不是每次击键时执行).

延迟WPF绑定没有问题 – 您只需使用绑定指定延迟：
< TextBlock Text =“{Binding Name,Delay = 500}”/>.

每当我需要在我使用Caliburn.Micro的Message.Attach的情况下延迟执行时,我通常以这种方式实现它(消息通过DoSomething操作附加到TextChanged事件)：

private int doingSomething;

public async void DoSomething()
{
    int current = ++doingSomething;
    await Task.Delay(500);
    if (current != doingSomething) //method was reentered
        return;

    await DoWorkCallServerEtc();
}

这很好用,但它不能很好地扩展并打破DRY原则(我需要在需要延迟的地方再次写入).

我的问题是,我能以某种方式使用Caliburn.Micro为此编写一个约定吗？
或者可能采用另一种更具可扩展性的方法

解决方法:

正如你在documentation page中所读到的那样

Actions feature leverages System.Windows.Interactivity for it’s
trigger mechanism.

这意味着

<TextBox Name="textBox" Margin="5"
    cal:Message.Attach="[Event TextChanged] = [Action DoAction(textBox.Text)]" />

相当于：

<TextBox Margin="5" Name="textBox">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="TextChanged">
            <cal:ActionMessage MethodName="DoAction">
                <cal:Parameter Value="{Binding ElementName=textBox, Path=Text}" />
            </cal:ActionMessage>
        </i:EventTrigger>
    </i:Interaction.Triggers>
</TextBox>

负责执行DoAction方法的对象是EventTrigger.AventTrigger立即触发,没有延迟.所以我们需要创建自己的DelayedEventTrigger;类似的东西：

public class DelayedEventTrigger : System.Windows.Interactivity.EventTrigger
{
    private EventArgs args;
    private DispatcherTimer dispatcherTimer;

    public static readonly DependencyProperty DelayProperty =
        DependencyProperty.Register("Delay", typeof(int), typeof(DelayedEventTrigger), new PropertyMetadata(1000));

    public int Delay
    {
        get { return (int)base.GetValue(DelayProperty); }
        set { base.SetValue(DelayProperty, value); }
    }

    protected override void OnEvent(EventArgs eventArgs)
    {
        if (dispatcherTimer != null)
        {
            dispatcherTimer.Stop();
        }
        args = eventArgs;
        dispatcherTimer = new DispatcherTimer();
        dispatcherTimer.Interval = TimeSpan.FromMilliseconds(Delay);
        dispatcherTimer.Tick += new EventHandler(OnDispatcherTimerTick);
        dispatcherTimer.Start();
    }

    protected override void OnDetaching()
    {
        if (dispatcherTimer != null)
        {
            dispatcherTimer.Stop();
            dispatcherTimer = null;
        }
        base.OnDetaching();
    }

    private void OnDispatcherTimerTick(object sender, EventArgs e)
    {
        dispatcherTimer.Stop();
        InvokeActions(args);
    }
}

其默认延迟为1秒(1000毫秒).所以现在我们可以在我们的XAML中使用它：

<TextBox Margin="5" Name="textBox">
    <i:Interaction.Triggers>
        <local:DelayedEventTrigger Delay="800" EventName="TextChanged">
            <cal:ActionMessage MethodName="DoDelayAction">
                <cal:Parameter Value="{Binding ElementName=textBox, Path=Text}" />
            </cal:ActionMessage>
        </local:DelayedEventTrigger>
    </i:Interaction.Triggers>
</TextBox>

在我看来,不需要使用约定(您可以显式使用DelayedEventTrigger),但是如果您需要,可以在Bootstrapper类中配置Caliburn Parser：

protected override void Configure()
{
    base.Configure();

    Parser.CreateTrigger = delegate(DependencyObject target, string triggerText)
    {
        System.Windows.Interactivity.EventTrigger eventTrigger;
        if (triggerText == null)
        {
            ElementConvention elementConvention = ConventionManager.GetElementConvention(target.GetType());
            return elementConvention.CreateTrigger();
        }
        string eventName = triggerText.Replace("[", String.Empty).Replace("]", String.Empty);
        if (eventName.StartsWith("Delayed", StringComparison.OrdinalIgnoreCase))
        {
            eventName = eventName.Replace("DelayedEvent", String.Empty).Trim();
            eventTrigger = new DelayedEventTrigger();
        }
        else
        {
            eventName = eventName.Replace("Event", String.Empty).Trim();
            eventTrigger = new System.Windows.Interactivity.EventTrigger();
        }

        eventTrigger.EventName = eventName;
        return eventTrigger;
    };     
}

通过添加此代码,您可以使用此约定：

<TextBox Name="textBox" Margin="5"
    cal:Message.Attach="[DelayedEvent TextChanged] = [Action DoDelayAction(textBox.Text)]" />

我希望它可以帮到你.

标签：c,wpf,async-await,caliburn-micro
来源： https://codeday.me/bug/20190623/1270155.html