c# - Caliburn.Micro，MVVM 模式 : CanExecute command doesn't work

Question

这是我的观点:

<StackPanel Orientation="Horizontal" VerticalAlignment="Top">
    <Label>Customer name:</Label>
    <TextBox Text="{Binding Customer.Name, UpdateSourceTrigger=PropertyChanged}" Width="136"/>
    <Button x:Name="UpdateClick">Update</Button>
</StackPanel>

这是我的 View 模型:

private Customer customer;
public Customer Customer
{
    get { return customer; }
    set { customer = value; NotifyOfPropertyChange(() => Customer); }
}

public bool CanUpdateClick 
{ 
    get 
    {
        if (string.IsNullOrEmpty(customer.Name))
        {
            return false;
        }
        return true; 
    } 
}

public void UpdateClick()
{
    //...
}

这是我的模型:

private string name;
public string Name
{
    get { return name; }
    set { name = value; NotifyOfPropertyChange(() => Name); }
}

所以我有 UpdateClick 方法，它工作得很好。我也有 CanUpdateClick 属性，但它不起作用，我不知道为什么？当文本框为空时，UI 上的按钮应该被禁用。请帮忙!

Answer 1

您可以订阅 Customer 类的 PropertyChanged 事件(因为您似乎是 PropertyChangedBase 的子类)并调用 NotifyOfPropertyChanged (() => CanUpdateClick) 当 Name 属性改变时:

// in your view model
// i'm assuming here that Customer is set before your view model is activated
protected override void OnActivate()
{
    base.OnActivate();
    Customer.PropertyChanged += CustomerPropertyChangedHandler;
}

protected override void OnDeactivate(bool close)
{
    base.OnDeactivate(close);
    // unregister handler
    Customer.PropertyChanged -= CustomerPropertyChangedHandler;
}

// event handler
protected void CustomerPropertyChangedHandler(object sender, PropertyChangedEventArgs e)
{
    if (e.PropertyName == nameof(Customer.Name))
    {
        NotifyOfPropertyChange(() => CanUpdateClick);
    }
}

或者，您可以只在 View 模型中创建一个 Name 或 CustomerName 属性来绑定(bind)，然后 a) 使用 Customer.Name 作为您的支持字段或 b) 使用普通支持字段，然后在更新时设置 Customer.Name:

在你看来:

<TextBox Text="{Binding CustomerName, UpdateSourceTrigger=PropertyChanged}" Width="136"/>

下面是如何在 View 模型中实现选项 a:

public string CustomerName
{
    get { return Customer.Name; }
    set
    {
        Customer.Name = value;
        NotifyOfPropertyChange(); // CallerMemberName goodness
        NotifyOfPropertyChange(() => CanUpdateClick);
    }
}