使用await和一个实现了CancelEventArgs的事件

本文关键字：实现 CancelEventArgs 事件 一个 await 使用 | 更新日期: 2023-09-27 18:10:14

我有一个类似的基类:

public abstract class PageBase
{
    public PageBase() { }
    public Task<object> Refresh(ModelRequirements requirements)
    {
        // does work of talking to server and getting data
    }
    private DataStates _dataState;
    public DataStates DataState()
    {
        get { _dataState = value; }
        set
        {
            var e = new DataStateChangingEventArgs();
            // the following method raises the changing event.
            // it does not return a task, and cannot be awaited.
            OnDataStateChanging(e);
            if (e.Cancel)
                return;
            _dataState = value;
        }
    }
    public event EventHandler<DataStateChangingEventArgs> DataStateChanging;
    protected virtual void OnDataStateChanging(DataStateChangingEventArgs e)
    {
        var dataStateChanging = DataStateChanging;
        if (DataStateChanging != null)
            DataStateChanging(this, e);
    }
}

我实现了一个这样的页面:

public class ContactsSearchPage : PageBase
{
    public ContactsSearchPage() { }
    private ContactModel Model {get; set;}
    protected async override void OnDataStateChanging(DataStateChangingEventArgs e)
    {
        // make new requirements
        var contactRequirements = new ContactRequirements();
        // Because the Refresh is awaited, it returns here and the rest 
        // of the DataState setter executes
        var refreshResult = await Refresh(contactRequirements);
        // set the property
        Model = refreshResult as ContactModel;
        // if the server returned null don't allow the data-state change to proceed
        if (Model == null)
            e.Cancel = true;
    }
}

等待刷新(在OnDataStateChanging覆盖中)是一个问题，因为它返回。没有使ondatastatechange返回任务，有解决方案，这种模式?

使用await和一个实现了CancelEventArgs的事件

期望属性setter将实际设置属性，并且它将在setter返回之前完成此操作。违反此期望将导致混乱。

这个模式有解决方案吗?

我建议把你的属性改成一个getter，和一个处理集合的方法:

public DataStates DataState { get; private set; }
public Task UpdateDataStateAsync()
{
   // ... Use await as necessary

这将使您的API与内部实际发生的匹配，并且更容易理解。

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