我为我的视图模型构建了一个基类。以下是部分代码:
public class BaseViewModel<TModel> : DependencyObject, INotifyPropertyChanged, IDisposable, IBaseViewModel<TModel>, IDataErrorInfo
{
public TModel Model { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (this._disposed)
{
return;
}
if (disposing)
{
this.Model = default(TModel);
}
this._disposed = true;
}
}
好的,所以我想,让我们在基类中添加一些验证,这使我得到了以下文章:Prism IDataErrorInfo validation with DataAnnotation on ViewModel Entities。所以我将以下方法/属性(IDataErrorInfo)添加到我的基类:
string IDataErrorInfo.Error
{
get { return null; }
}
string IDataErrorInfo.this[string columnName]
{
get { return ValidateProperty(columnName); }
}
protected virtual string ValidateProperty(string columnName)
{
// get cached property accessors
var propertyGetters = GetPropertyGetterLookups(GetType());
if (propertyGetters.ContainsKey(columnName))
{
// read value of given property
var value = propertyGetters[columnName](this);
// run validation
var results = new List<ValidationResult>();
var vc = new ValidationContext(this, null, null) { MemberName = columnName };
Validator.TryValidateProperty(value, vc, results);
// transpose results
var errors = Array.ConvertAll(results.ToArray(), o => o.ErrorMessage);
return string.Join(Environment.NewLine, errors);
}
return string.Empty;
}
private static Dictionary<string, Func<object, object>> GetPropertyGetterLookups(Type objType)
{
var key = objType.FullName ?? "";
if (!PropertyLookupCache.ContainsKey(key))
{
var o = objType.GetProperties()
.Where(p => GetValidations(p).Length != 0)
.ToDictionary(p => p.Name, CreatePropertyGetter);
PropertyLookupCache[key] = o;
return o;
}
return (Dictionary<string, Func<object, object>>)PropertyLookupCache[key];
}
private static Func<object, object> CreatePropertyGetter(PropertyInfo propertyInfo)
{
var instanceParameter = System.Linq.Expressions.Expression.Parameter(typeof(object), "instance");
var expression = System.Linq.Expressions.Expression.Lambda<Func<object, object>>(
System.Linq.Expressions.Expression.ConvertChecked(
System.Linq.Expressions.Expression.MakeMemberAccess(
System.Linq.Expressions.Expression.ConvertChecked(instanceParameter, propertyInfo.DeclaringType),
propertyInfo),
typeof(object)),
instanceParameter);
var compiledExpression = expression.Compile();
return compiledExpression;
}
private static ValidationAttribute[] GetValidations(PropertyInfo property)
{
return (ValidationAttribute[])property.GetCustomAttributes(typeof(ValidationAttribute), true);
}
好的,这让我想到了这个问题。事情是验证工作完美,但是假设我有一个带有StringLength属性的属性(在我的视图模型中称为:Person)。一旦打开应用程序,就会触发StringLength属性。用户甚至没有机会做任何事情。一旦应用程序启动,验证就会触发。
public class PersonViewModel : BaseViewModel<BaseProxyWrapper<PosServiceClient>>
{
private string _password = string.Empty;
[StringLength(10, MinimumLength = 3, ErrorMessage = "Password must be between 3 and 10 characters long")]
public string Password
{
get { return this._password; }
set
{
if (this._password != value)
{
this._password = value;
this.OnPropertyChanged("Password");
}
}
}
}
我注意到这是由IDataErrorInfo.this[string columnName]
属性引起的,而后者又调用了ValidateProperty
方法。但是,我不知道如何解决这个问题?
答案 0 :(得分:2)
可能有两个问题......
您是否使用公共属性填充yopur Person
实例?
e.g。
new Person { Password = null }
这将触发密码的属性更改通知,并将验证它。
一些开发人员还在构造函数中设置属性......
public class Person {
public Person() {
this.Password = null;
}
}
建议的做法是使用私人字段......
public class Person {
public Person() {
_password = null;
}
public Person(string pwd) {
_password = pwd;
}
}
OR
您可以在我们的视图模型库中创建一个标记IsLoaded
。确保在加载UI后(可能在UI.Loaded
事件中)将其设置为true。在IDataErrorInfo.this[string columnName]
中检查此属性是否为true,然后才验证值。否则返回null。
[编辑]
以下更改完成了这项工作:
public class PersonViewModel : BaseViewModel<BaseProxyWrapper<PosServiceClient>>
{
private string _password;
[StringLength(10, MinimumLength = 3, ErrorMessage = "Password must be between 3 and 10 characters long")]
public string Password
{
get { return this._password; }
set
{
if (this._password != value)
{
this._password = value;
this.OnPropertyChanged("Password");
}
}
}
public PersonViewModel(BaseProxyWrapper<PosServiceClient> model)
: base(model)
{
this._username = null;
}
}
答案 1 :(得分:0)
我过去做过的事情是将更新源触发器更改为显式,创建一个在TextBox失去焦点时更新源的行为,然后将该行为附加到TextBox。