强制INotifyDataErrorInfo验证

Question

我完全按照以下链接中的描述实现了INotifyDataErrorInfo:

http://blog.micic.ch/net/easy-mvvm-example-with-inotifypropertychanged-and-inotifydataerrorinfo

我有一个TextBox绑定到我的模型中的字符串属性.

XAML

<TextBox Text="{Binding FullName,
                        ValidatesOnNotifyDataErrors=True,
                        NotifyOnValidationError=True,
                        UpdateSourceTrigger=PropertyChanged}" />

模型

private string _fullName;
public string FullName
{
    get { return _fullName; }
    set
    {
        // Set raises OnPropertyChanged
        Set(ref _fullName, value);

        if (string.IsNullOrWhiteSpace(_fullName))
            AddError(nameof(FullName), "Name required");
        else
            RemoveError(nameof(FullName));                
    }
}

INotifyDataError代码

private Dictionary<string, List<string>> _errors = new Dictionary<string, List<string>>();

public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;

// get errors by property
public IEnumerable GetErrors(string propertyName)
{
    if (_errors.ContainsKey(propertyName))
        return _errors[propertyName];
    return null;
}

public bool HasErrors => _errors.Count > 0;

// object is valid
public bool IsValid => !HasErrors;

public void AddError(string propertyName, string error)
{
    // Add error to list
    _errors[propertyName] = new List<string>() { error };
    NotifyErrorsChanged(propertyName);
}

public void RemoveError(string propertyName)
{
    // remove error
    if (_errors.ContainsKey(propertyName))
        _errors.Remove(propertyName);
    NotifyErrorsChanged(propertyName);
}

public void NotifyErrorsChanged(string propertyName)
{
    // Notify
    if (ErrorsChanged != null)
       ErrorsChanged(this, new DataErrorsChangedEventArgs(propertyName));
}

现在这一切都运行正常,但只有在我的TextBox中输入内容时才会验证.我想要一些方法来按需验证,甚至没有触摸文本框,比如按一下按钮.

我已经尝试过为我的所有属性提升PropertyChanged,如本问题所述,但它没有检测到错误.我不知何故需要调用我的属性设置器,以便可以检测到错误.我正在寻找一个MVVM解决方案.

Answer 1

你使用的INotifyDataErrorInfo实现有点瑕疵恕我直言.它依赖于附加到对象的状态(列表)中保存的错误.存储状态的问题有时在移动的世界中,您没有机会在需要时更新它.这是另一个MVVM实现,它不依赖于存储状态,但可以动态计算错误状态.

由于您需要将验证代码放在一个集中的GetErrors方法中(您可以创建从此中心方法调用的每个属性验证方法),而不是在属性设置器中,因此处理的方式有所不同.

public class ModelBase : INotifyPropertyChanged, INotifyDataErrorInfo
{
    public event PropertyChangedEventHandler PropertyChanged;
    public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;

    public bool HasErrors
    {
        get
        {
            return GetErrors(null).OfType<object>().Any();
        }
    }

    public virtual void ForceValidation()
    {
        OnPropertyChanged(null);
    }

    public virtual IEnumerable GetErrors([CallerMemberName] string propertyName = null)
    {
        return Enumerable.Empty<object>();
    }

    protected void OnErrorsChanged([CallerMemberName] string propertyName = null)
    {
        OnErrorsChanged(this, new DataErrorsChangedEventArgs(propertyName));
    }

    protected virtual void OnErrorsChanged(object sender, DataErrorsChangedEventArgs e)
    {
        var handler = ErrorsChanged;
        if (handler != null)
        {
            handler(sender, e);
        }
    }

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        OnPropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    protected virtual void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        var handler = PropertyChanged;
        if (handler != null)
        {
            handler(sender, e);
        }
    }
}

这里有两个示例类,演示如何使用它:

public class Customer : ModelBase
{
    private string _name;

    public string Name
    {
        get
        {
            return _name;
        }
        set
        {
            if (_name != value)
            {
                _name = value;
                OnPropertyChanged();
            }
        }
    }

    public override IEnumerable GetErrors([CallerMemberName] string propertyName = null)
    {
        if (string.IsNullOrEmpty(propertyName) || propertyName == nameof(Name))
        {
            if (string.IsNullOrWhiteSpace(_name))
                yield return "Name cannot be empty.";
        }
    }
}

public class CustomerWithAge : Customer
{
    private int _age;
    public int Age
    {
        get
        {
            return _age;
        }
        set
        {
            if (_age != value)
            {
                _age = value;
                OnPropertyChanged();
            }
        }
    }

    public override IEnumerable GetErrors([CallerMemberName] string propertyName = null)
    {
        foreach (var obj in base.GetErrors(propertyName))
        {
            yield return obj;
        }

        if (string.IsNullOrEmpty(propertyName) || propertyName == nameof(Age))
        {
            if (_age <= 0)
                yield return "Age is invalid.";
        }
    }
}

它就像一个带有简单XAML的魅力,如下所示:

<TextBox Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}" />
<TextBox Text="{Binding Age, UpdateSourceTrigger=PropertyChanged}" />

(UpdateSourceTrigger是可选的,如果你不使用它,它只会在焦点丢失时起作用).

使用此MVVM基类,您不必强制进行任何验证.但是,如果你需要它,我在ModelBase中添加了一个ForceValidation示例方法应该可以工作(我已经测试了它,例如像_name这样的成员值,如果没有通过公共setter就会被更改).

Answer 2

最好的选择是使用继电器命令界面。看看这个：

public class RelayCommand : ICommand
{
    Action _TargetExecuteMethod;
    Func<bool> _TargetCanExecuteMethod;

    public RelayCommand(Action executeMethod)
    {
        _TargetExecuteMethod = executeMethod;
    }

    public RelayCommand(Action executeMethod, Func<bool> canExecuteMethod)
    {
        _TargetExecuteMethod = executeMethod;
        _TargetCanExecuteMethod = canExecuteMethod;
    }

    public void RaiseCanExecuteChanged()
    {
        CanExecuteChanged(this, EventArgs.Empty);
    }
    #region ICommand Members

    bool ICommand.CanExecute(object parameter)
    {
        if (_TargetCanExecuteMethod != null)
        {
            return _TargetCanExecuteMethod();
        }
        if (_TargetExecuteMethod != null)
        {
            return true;
        }
        return false;
    }

    public event EventHandler CanExecuteChanged = delegate { };

    void ICommand.Execute(object parameter)
    {
        if (_TargetExecuteMethod != null)
        {
            _TargetExecuteMethod();
        }
    }
    #endregion
}

您可以在视图模型中声明此中继命令，如下所示：

public RelayCommand SaveCommand { get; private set; }

现在，除了注册SaveCommandwithOnSave和 aCanSave方法之外，由于您扩展自，您还INotifyDataErrorInfo可以在构造函数中注册：ErrorsChanged

public YourViewModel()
{
    SaveCommand = new RelayCommand(OnSave, CanSave);
    ErrorsChanged += RaiseCanExecuteChanged;
}

你需要以下方法：

private void RaiseCanExecuteChanged(object sender, EventArgs e)
{
        SaveCommand.RaiseCanExecuteChanged();
}

public bool CanSave()
{
    return !this.HasErrors;
}

private void OnSave()
{
    //Your save logic here.
}

另外，每次调用后PropertyChanged，您都可以调用此验证方法：

    private void ValidateProperty<T>(string propertyName, T value)
    {
        var results = new List<ValidationResult>();
        ValidationContext context = new ValidationContext(this);
        context.MemberName = propertyName;
        Validator.TryValidateProperty(value, context, results);

        if (results.Any())
        {
            _errors[propertyName] = results.Select(c => c.ErrorMessage).ToList();
        }
        else
        {
            _errors.Remove(propertyName);
        }

        ErrorsChanged(this, new DataErrorsChangedEventArgs(propertyName));
    }

通过此设置，如果您的视图模型均从INotifyPropertyChanged和INotifyDataErrorInfo（或从从这两个扩展的基类）扩展，则当您将按钮绑定到上面时SaveCommand，如果存在验证错误，WPF 框架将自动禁用它。

希望这可以帮助。