我应该如何使用 Avalonia(ReactiveUI) 控制命令的可执行性？

Posted 2023-03-31

【中文标题】我应该如何使用 Avalonia(ReactiveUI) 控制命令的可执行性？

【英文标题】：How should I make a controlling executability of command using Avalonia(ReactiveUI)?

【发布时间】：2021-08-25 23:21:32

【问题描述】：

我正在尝试根据本指南实现控制 ReactiveUI 命令的可执行性：guide. 但是我遇到了一个异常：“由于对象的当前状态，操作无效。” 我应该如何解决这个问题？ 我的代码示例：

public class CreateBookViewModel : ViewModelBase

    IObservable<bool> canExecuteCreateBookCommand;
    private string? name;
    private string? path;
    public ReactiveCommand<Unit, Unit> ChangePathCommand  get; 
    public ReactiveCommand<Unit, EditBookViewModel?> CreateBookCommand  get; 


    public string? Name 
    
        get => name;
        set => this.RaiseAndSetIfChanged(ref name, value);
    
    public string? Path
    
        get => path;
        set => this.RaiseAndSetIfChanged(ref path, value);
    

    public CreateBookViewModel()
    
        canExecuteCreateBookCommand = this.WhenAnyValue(x => x.path, x => x.name, (name, path) =>
            !string.IsNullOrWhiteSpace(name) && !string.IsNullOrWhiteSpace(path));
        ChangePathCommand = ReactiveCommand.CreateFromTask(RunChangePath);
        CreateBookCommand = ReactiveCommand.Create(RunCreateBook, canExecuteCreateBookCommand);
    

    private async Task RunChangePath()
    
       var dialog = new OpenFolderDialog();
       Path = await dialog.ShowAsync(CreateBookWindow.Instance);
    

    private  EditBookViewModel? RunCreateBook()
    
        if(name!= null && path!= null)
        
            EditBookViewModel book = new EditBookViewModel(name, path);
            return book;
        
        return null;
    

【参考方案1】：

在this.WhenAnyValue 中，您的选择器表达式指向字段而不是属性。将其更改为 this.WhenAnyValue(x => x.Path, x => x.Name, (name, path) => !string.IsNullOrWhiteSpace(name) && !string.IsNullOrWhiteSpace(path));.