Xamarin MvvmCross ViewModel 验证
Xamarin MvvmCross ViewModel Validation
我目前正在构建我的第一个 Xamarin MvvmCross 应用程序，我目前正在考虑验证用户对视图模型的输入。
对这个插件进行了大量搜索（包括 MvvmCross 团队）link：
此插件使用了非常旧的 MvvmCross v3 版本。我尝试从这个插件中获取代码并将其直接构建到我的应用程序核心项目中，直到我遇到 Bindings 重大更改。然后我得出结论，为了使用最新版本的 MvvmCross，这个插件实际上需要完全重写。
所以我现在有点卡住了。
目前推荐的在视图模型中执行输入验证的最佳方法是什么？
编辑：在 GitHub https://github.com/kiliman/mvx-samples/tree/master/MvxSamples.Validation
上添加示例项目
我使用 MVVM 验证助手 http://www.nuget.org/packages/MvvmValidation/
这是一个简单易用的验证库。它与 MvvmCross 无关。
下面是我如何使用它，例如，在我的 SigninViewModel 中：
private async void DoSignin()
{
try
{
if (!Validate())
{
return;
}
IsBusy = true;
Result = "";
var success = await SigninService.SigninAsync(Email, Password);
if (success)
{
Result = "";
ShowViewModel<HomeViewModel>();
Close();
return;
}
Result = "Invalid email/password. Please try again.";
}
catch (Exception ex)
{
Result = "Error occured during sign in.";
Mvx.Error(ex.ToString());
}
finally
{
IsBusy = false;
}
}
private bool Validate()
{
var validator = new ValidationHelper();
validator.AddRequiredRule(() => Email, "Email is required.");
validator.AddRequiredRule(() => Password, "Password is required.");
var result = validator.ValidateAll();
Errors = result.AsObservableDictionary();
return result.IsValid;
}
它的好处是您可以将错误作为一个集合获取并将它们绑定到您的视图中。对于 Android，我将错误 [=38=] 设置为键控错误消息。
<EditText
android:minHeight="40dp"
android:layout_margin="4dp"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:inputType="textEmailAddress"
android:hint="Email"
local:MvxBind="Text Email; Error Errors['Email']"
android:id="@+id/EmailEditText" />
<EditText
android:minHeight="40dp"
android:layout_margin="4dp"
android:inputType="textPassword"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="Password"
local:MvxBind="Text Password; Error Errors['Password']"
android:id="@+id/PasswordEditText" />
下面是验证的样子：
编辑：显示助手代码
public static class ValidationResultExtension
{
public static ObservableDictionary<string, string> AsObservableDictionary(this ValidationResult result)
{
var dictionary = new ObservableDictionary<string, string>();
foreach (var item in result.ErrorList)
{
var key = item.Target.ToString();
var text = item.ErrorText;
if (dictionary.ContainsKey(key))
{
dictionary[key] = dictionary.Keys + Environment.NewLine + text;
}
else
{
dictionary[key] = text;
}
}
return dictionary;
}
}
public class ObservableDictionary<TKey, TValue> : IDictionary<TKey, TValue>, INotifyCollectionChanged, INotifyPropertyChanged
{
private const string CountString = "Count";
private const string IndexerName = "Item[]";
private const string KeysName = "Keys";
private const string ValuesName = "Values";
private IDictionary<TKey, TValue> _dictionary;
protected IDictionary<TKey, TValue> Dictionary
{
get { return _dictionary; }
}
public ObservableDictionary()
{
_dictionary = new Dictionary<TKey, TValue>();
}
public ObservableDictionary(IDictionary<TKey, TValue> dictionary)
{
_dictionary = new Dictionary<TKey, TValue>(dictionary);
}
public ObservableDictionary(IEqualityComparer<TKey> comparer)
{
_dictionary = new Dictionary<TKey, TValue>(comparer);
}
public ObservableDictionary(int capacity)
{
_dictionary = new Dictionary<TKey, TValue>(capacity);
}
public ObservableDictionary(IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer)
{
_dictionary = new Dictionary<TKey, TValue>(dictionary, comparer);
}
public ObservableDictionary(int capacity, IEqualityComparer<TKey> comparer)
{
_dictionary = new Dictionary<TKey, TValue>(capacity, comparer);
}
#region IDictionary<TKey,TValue> Members
public void Add(TKey key, TValue value)
{
Insert(key, value, true);
}
public bool ContainsKey(TKey key)
{
return Dictionary.ContainsKey(key);
}
public ICollection<TKey> Keys
{
get { return Dictionary.Keys; }
}
public bool Remove(TKey key)
{
if (key == null)
{
throw new ArgumentNullException("key");
}
TValue value;
Dictionary.TryGetValue(key, out value);
var removed = Dictionary.Remove(key);
if (removed)
{
OnCollectionChanged(NotifyCollectionChangedAction.Remove, new KeyValuePair<TKey, TValue>(key, value));
}
return removed;
}
public bool TryGetValue(TKey key, out TValue value)
{
return Dictionary.TryGetValue(key, out value);
}
public ICollection<TValue> Values
{
get { return Dictionary.Values; }
}
public TValue this[TKey key]
{
get
{
return Dictionary.ContainsKey(key) ? Dictionary[key] : default(TValue);
}
set
{
Insert(key, value, false);
}
}
#endregion IDictionary<TKey,TValue> Members
public void Add(KeyValuePair<TKey, TValue> item)
{
Insert(item.Key, item.Value, true);
}
public void Clear()
{
if (Dictionary.Count > 0)
{
Dictionary.Clear();
OnCollectionChanged();
}
}
public bool Contains(KeyValuePair<TKey, TValue> item)
{
return Dictionary.Contains(item);
}
public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
{
Dictionary.CopyTo(array, arrayIndex);
}
public int Count
{
get { return Dictionary.Count; }
}
public bool IsReadOnly
{
get { return Dictionary.IsReadOnly; }
}
public bool Remove(KeyValuePair<TKey, TValue> item)
{
return Remove(item.Key);
}
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
{
return Dictionary.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return ((IEnumerable)Dictionary).GetEnumerator();
}
public event NotifyCollectionChangedEventHandler CollectionChanged;
public event PropertyChangedEventHandler PropertyChanged;
public void AddRange(IDictionary<TKey, TValue> items)
{
if (items == null)
{
throw new ArgumentNullException("items");
}
if (items.Count > 0)
{
if (Dictionary.Count > 0)
{
if (items.Keys.Any((k) => Dictionary.ContainsKey(k)))
{
throw new ArgumentException("An item with the same key has already been added.");
}
else
{
foreach (var item in items)
{
Dictionary.Add(item);
}
}
}
else
{
_dictionary = new Dictionary<TKey, TValue>(items);
}
OnCollectionChanged(NotifyCollectionChangedAction.Add, items.ToArray());
}
}
private void Insert(TKey key, TValue value, bool add)
{
if (key == null)
{
throw new ArgumentNullException("key");
}
TValue item;
if (Dictionary.TryGetValue(key, out item))
{
if (add)
{
throw new ArgumentException("An item with the same key has already been added.");
}
if (Equals(item, value))
{
return;
}
Dictionary[key] = value;
OnCollectionChanged(NotifyCollectionChangedAction.Replace, new KeyValuePair<TKey, TValue>(key, value), new KeyValuePair<TKey, TValue>(key, item));
}
else
{
Dictionary[key] = value;
OnCollectionChanged(NotifyCollectionChangedAction.Add, new KeyValuePair<TKey, TValue>(key, value));
}
}
private void OnPropertyChanged()
{
OnPropertyChanged(CountString);
OnPropertyChanged(IndexerName);
OnPropertyChanged(KeysName);
OnPropertyChanged(ValuesName);
}
protected virtual void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private void OnCollectionChanged()
{
OnPropertyChanged();
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
}
private void OnCollectionChanged(NotifyCollectionChangedAction action, KeyValuePair<TKey, TValue> changedItem)
{
OnPropertyChanged();
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(action, changedItem));
}
}
private void OnCollectionChanged(NotifyCollectionChangedAction action, KeyValuePair<TKey, TValue> newItem, KeyValuePair<TKey, TValue> oldItem)
{
OnPropertyChanged();
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(action, newItem, oldItem));
}
}
private void OnCollectionChanged(NotifyCollectionChangedAction action, IList newItems)
{
OnPropertyChanged();
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(action, newItems));
}
}
}
确实没有固定的推荐，这是您最满意的。我发现很多选项特别冗长（即需要大量样板代码，即使有一些辅助库）。
我登陆的图书馆是FluentValidation for writing the rules (and they have a lot of common ones built-in and great ways for re-use/customization, including context-specific rules), and to reduce a lot of the complication and lines of code required, wrote a little helper library of my own which can be seen here (complete with example): FluentValidation MVVM Plugin
那里的示例使用了 Prism，但它完全不依赖于任何 MVVM 框架。
下面是示例：
Class 到 build/validate:
public class Email
{
public string RecipientEmailAddress { get; set; }
public string RecipientName { get; set; }
}
ViewModel 中的属性使用我的库中提供的 Validatable 对象，以及 Fody.PropertyChanged（这也将为 INPC 节省大量样板代码） :
public Validatable<string> RecipientName { get; set; } = new Validatable<string>(nameof(Email.RecipientName));
public Validatable<string> EmailAddress { get; set; } = new Validatable<string>(nameof(Email.RecipientEmailAddress));
为 class:
创建 FluentValidation AbstractValidator
public class EmailValidator : AbstractValidator<Email>
{
public EmailValidator()
{
RuleFor(e => e.RecipientEmailAddress)
.Cascade(CascadeMode.StopOnFirstFailure)
.NotEmpty()
.EmailAddress();
RuleFor(e => e.RecipientName)
.NotEmpty();
When(e => e.RecipientName != null, () =>
{
RuleFor(e => e.RecipientName)
.MinimumLength(3).WithMessage("How you bout to enter a FULL 'name' with less than 3 chars!?")
.Must(name => name.Contains(" ")).WithMessage("Expecting at least first and last name separated by a space!");
});
}
}
在您的 ViewModel 中实施 IValidate：
public void SetupForValidation() // to be called from your ViewModel's constructor
{
// set validators and prop groups
_emailValidator = new EmailValidator();
_emailValidatables = new Validatables(RecipientName, EmailAddress);
// maybe even set some defaults
RecipientName.Value = "Fred Fredovich";
}
public OverallValidationResult Validate(Email email)
{
return _emailValidator.Validate(email).ApplyResultsTo(_emailValidatables);
}
public void ClearValidation(string clearOptions = "")
{
_emailValidatables.Clear(clearOptions);
}
实施命令（以下示例使用 Prism 的 DelegateCommand，但显然这不是必需的）以使用这些方法：
private DelegateCommand<string> _clearValidationCommand;
private DelegateCommand _validateEmailCommand;
public DelegateCommand<string> ClearValidationCommand =>
_clearValidationCommand ?? (_clearValidationCommand = new DelegateCommand<string>(ClearValidation)); // already defined above in step 4 as part of the interface requirements
public DelegateCommand ValidateEmailCommand =>
_validateEmailCommand ?? (_validateEmailCommand = new DelegateCommand(ExecuteValidateEmailCommand));
public void ExecuteValidateEmailCommand()
{
var email = _emailValidatables.Populate<Email>(); // this conveniently creates a new Email instance with the values from our Validatable objects (populated by the user via the View)
var overallValidationResult = Validate(email); // remember, this will also populate each individual Validatable's IsValid status and Errors list.
if (overallValidationResult.IsValidOverall)
{
// do something with the validated email instance
}
else
{
// do something else
}
if (overallValidationResult.NonSplitErrors.Any())
{
// do something with errors that don't pertain to any of our Validatables (which is not possible in our little example here)
}
}
最后，视图（在本例中为 XAML）：
<Entry
Placeholder="Email"
Text="{Binding EmailAddress.Value}">
<Entry.Behaviors>
<!-- Note this behavior is included in the Prism Library -->
<behaviors:EventToCommandBehavior
Command="{Binding ClearValidationCommand}"
CommandParameter="RecipientEmailAddress"
EventName="Focused" />
</Entry.Behaviors>
</Entry>
<Label
Style="{StaticResource ErrorLabelStyle}"
Text="{Binding EmailAddress.FirstError}" />
<Button
Command="{Binding ValidateEmailCommand}"
Text="Validate" />
这可能是最常见的用例 - 我们有：
- 接受用户输入的条目（只显示 1 个而不是每个 属性
- 为简洁起见）
- 将执行验证的按钮
- 一个标签，显示条目下可能存在的许多错误中的第一个，或者 none 当然
- 如果验证成功
- 用户再次激活条目后清除验证错误标签的行为（可能是为了修复错误）
但您也可以使用一个按钮来一次清除所有验证，甚至连同实际值一起清除（清除整个表单）等 - 只需通读 [=76] 中的完整示例=] 到 repo，以及使用它的完整工作的 Xamarin 示例项目（其中包括一些更高级的示例，例如使用基于上下文的规则）。
希望这对您有所帮助...
我目前正在构建我的第一个 Xamarin MvvmCross 应用程序，我目前正在考虑验证用户对视图模型的输入。
对这个插件进行了大量搜索（包括 MvvmCross 团队）link：
此插件使用了非常旧的 MvvmCross v3 版本。我尝试从这个插件中获取代码并将其直接构建到我的应用程序核心项目中，直到我遇到 Bindings 重大更改。然后我得出结论，为了使用最新版本的 MvvmCross，这个插件实际上需要完全重写。
所以我现在有点卡住了。
目前推荐的在视图模型中执行输入验证的最佳方法是什么？
编辑：在 GitHub https://github.com/kiliman/mvx-samples/tree/master/MvxSamples.Validation
上添加示例项目我使用 MVVM 验证助手 http://www.nuget.org/packages/MvvmValidation/
这是一个简单易用的验证库。它与 MvvmCross 无关。
下面是我如何使用它，例如，在我的 SigninViewModel 中：
private async void DoSignin()
{
try
{
if (!Validate())
{
return;
}
IsBusy = true;
Result = "";
var success = await SigninService.SigninAsync(Email, Password);
if (success)
{
Result = "";
ShowViewModel<HomeViewModel>();
Close();
return;
}
Result = "Invalid email/password. Please try again.";
}
catch (Exception ex)
{
Result = "Error occured during sign in.";
Mvx.Error(ex.ToString());
}
finally
{
IsBusy = false;
}
}
private bool Validate()
{
var validator = new ValidationHelper();
validator.AddRequiredRule(() => Email, "Email is required.");
validator.AddRequiredRule(() => Password, "Password is required.");
var result = validator.ValidateAll();
Errors = result.AsObservableDictionary();
return result.IsValid;
}
它的好处是您可以将错误作为一个集合获取并将它们绑定到您的视图中。对于 Android，我将错误 [=38=] 设置为键控错误消息。
<EditText
android:minHeight="40dp"
android:layout_margin="4dp"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:inputType="textEmailAddress"
android:hint="Email"
local:MvxBind="Text Email; Error Errors['Email']"
android:id="@+id/EmailEditText" />
<EditText
android:minHeight="40dp"
android:layout_margin="4dp"
android:inputType="textPassword"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="Password"
local:MvxBind="Text Password; Error Errors['Password']"
android:id="@+id/PasswordEditText" />
下面是验证的样子：
编辑：显示助手代码
public static class ValidationResultExtension
{
public static ObservableDictionary<string, string> AsObservableDictionary(this ValidationResult result)
{
var dictionary = new ObservableDictionary<string, string>();
foreach (var item in result.ErrorList)
{
var key = item.Target.ToString();
var text = item.ErrorText;
if (dictionary.ContainsKey(key))
{
dictionary[key] = dictionary.Keys + Environment.NewLine + text;
}
else
{
dictionary[key] = text;
}
}
return dictionary;
}
}
public class ObservableDictionary<TKey, TValue> : IDictionary<TKey, TValue>, INotifyCollectionChanged, INotifyPropertyChanged
{
private const string CountString = "Count";
private const string IndexerName = "Item[]";
private const string KeysName = "Keys";
private const string ValuesName = "Values";
private IDictionary<TKey, TValue> _dictionary;
protected IDictionary<TKey, TValue> Dictionary
{
get { return _dictionary; }
}
public ObservableDictionary()
{
_dictionary = new Dictionary<TKey, TValue>();
}
public ObservableDictionary(IDictionary<TKey, TValue> dictionary)
{
_dictionary = new Dictionary<TKey, TValue>(dictionary);
}
public ObservableDictionary(IEqualityComparer<TKey> comparer)
{
_dictionary = new Dictionary<TKey, TValue>(comparer);
}
public ObservableDictionary(int capacity)
{
_dictionary = new Dictionary<TKey, TValue>(capacity);
}
public ObservableDictionary(IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer)
{
_dictionary = new Dictionary<TKey, TValue>(dictionary, comparer);
}
public ObservableDictionary(int capacity, IEqualityComparer<TKey> comparer)
{
_dictionary = new Dictionary<TKey, TValue>(capacity, comparer);
}
#region IDictionary<TKey,TValue> Members
public void Add(TKey key, TValue value)
{
Insert(key, value, true);
}
public bool ContainsKey(TKey key)
{
return Dictionary.ContainsKey(key);
}
public ICollection<TKey> Keys
{
get { return Dictionary.Keys; }
}
public bool Remove(TKey key)
{
if (key == null)
{
throw new ArgumentNullException("key");
}
TValue value;
Dictionary.TryGetValue(key, out value);
var removed = Dictionary.Remove(key);
if (removed)
{
OnCollectionChanged(NotifyCollectionChangedAction.Remove, new KeyValuePair<TKey, TValue>(key, value));
}
return removed;
}
public bool TryGetValue(TKey key, out TValue value)
{
return Dictionary.TryGetValue(key, out value);
}
public ICollection<TValue> Values
{
get { return Dictionary.Values; }
}
public TValue this[TKey key]
{
get
{
return Dictionary.ContainsKey(key) ? Dictionary[key] : default(TValue);
}
set
{
Insert(key, value, false);
}
}
#endregion IDictionary<TKey,TValue> Members
public void Add(KeyValuePair<TKey, TValue> item)
{
Insert(item.Key, item.Value, true);
}
public void Clear()
{
if (Dictionary.Count > 0)
{
Dictionary.Clear();
OnCollectionChanged();
}
}
public bool Contains(KeyValuePair<TKey, TValue> item)
{
return Dictionary.Contains(item);
}
public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
{
Dictionary.CopyTo(array, arrayIndex);
}
public int Count
{
get { return Dictionary.Count; }
}
public bool IsReadOnly
{
get { return Dictionary.IsReadOnly; }
}
public bool Remove(KeyValuePair<TKey, TValue> item)
{
return Remove(item.Key);
}
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
{
return Dictionary.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return ((IEnumerable)Dictionary).GetEnumerator();
}
public event NotifyCollectionChangedEventHandler CollectionChanged;
public event PropertyChangedEventHandler PropertyChanged;
public void AddRange(IDictionary<TKey, TValue> items)
{
if (items == null)
{
throw new ArgumentNullException("items");
}
if (items.Count > 0)
{
if (Dictionary.Count > 0)
{
if (items.Keys.Any((k) => Dictionary.ContainsKey(k)))
{
throw new ArgumentException("An item with the same key has already been added.");
}
else
{
foreach (var item in items)
{
Dictionary.Add(item);
}
}
}
else
{
_dictionary = new Dictionary<TKey, TValue>(items);
}
OnCollectionChanged(NotifyCollectionChangedAction.Add, items.ToArray());
}
}
private void Insert(TKey key, TValue value, bool add)
{
if (key == null)
{
throw new ArgumentNullException("key");
}
TValue item;
if (Dictionary.TryGetValue(key, out item))
{
if (add)
{
throw new ArgumentException("An item with the same key has already been added.");
}
if (Equals(item, value))
{
return;
}
Dictionary[key] = value;
OnCollectionChanged(NotifyCollectionChangedAction.Replace, new KeyValuePair<TKey, TValue>(key, value), new KeyValuePair<TKey, TValue>(key, item));
}
else
{
Dictionary[key] = value;
OnCollectionChanged(NotifyCollectionChangedAction.Add, new KeyValuePair<TKey, TValue>(key, value));
}
}
private void OnPropertyChanged()
{
OnPropertyChanged(CountString);
OnPropertyChanged(IndexerName);
OnPropertyChanged(KeysName);
OnPropertyChanged(ValuesName);
}
protected virtual void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private void OnCollectionChanged()
{
OnPropertyChanged();
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
}
private void OnCollectionChanged(NotifyCollectionChangedAction action, KeyValuePair<TKey, TValue> changedItem)
{
OnPropertyChanged();
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(action, changedItem));
}
}
private void OnCollectionChanged(NotifyCollectionChangedAction action, KeyValuePair<TKey, TValue> newItem, KeyValuePair<TKey, TValue> oldItem)
{
OnPropertyChanged();
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(action, newItem, oldItem));
}
}
private void OnCollectionChanged(NotifyCollectionChangedAction action, IList newItems)
{
OnPropertyChanged();
if (CollectionChanged != null)
{
CollectionChanged(this, new NotifyCollectionChangedEventArgs(action, newItems));
}
}
}
确实没有固定的推荐，这是您最满意的。我发现很多选项特别冗长（即需要大量样板代码，即使有一些辅助库）。
我登陆的图书馆是FluentValidation for writing the rules (and they have a lot of common ones built-in and great ways for re-use/customization, including context-specific rules), and to reduce a lot of the complication and lines of code required, wrote a little helper library of my own which can be seen here (complete with example): FluentValidation MVVM Plugin
那里的示例使用了 Prism，但它完全不依赖于任何 MVVM 框架。
下面是示例：
Class 到 build/validate:
public class Email
{
public string RecipientEmailAddress { get; set; }
public string RecipientName { get; set; }
}
ViewModel 中的属性使用我的库中提供的 Validatable 对象，以及 Fody.PropertyChanged（这也将为 INPC 节省大量样板代码） :
public Validatable<string> RecipientName { get; set; } = new Validatable<string>(nameof(Email.RecipientName));
public Validatable<string> EmailAddress { get; set; } = new Validatable<string>(nameof(Email.RecipientEmailAddress));
为 class:
创建 FluentValidation AbstractValidatorpublic class EmailValidator : AbstractValidator<Email>
{
public EmailValidator()
{
RuleFor(e => e.RecipientEmailAddress)
.Cascade(CascadeMode.StopOnFirstFailure)
.NotEmpty()
.EmailAddress();
RuleFor(e => e.RecipientName)
.NotEmpty();
When(e => e.RecipientName != null, () =>
{
RuleFor(e => e.RecipientName)
.MinimumLength(3).WithMessage("How you bout to enter a FULL 'name' with less than 3 chars!?")
.Must(name => name.Contains(" ")).WithMessage("Expecting at least first and last name separated by a space!");
});
}
}
在您的 ViewModel 中实施 IValidate：
public void SetupForValidation() // to be called from your ViewModel's constructor
{
// set validators and prop groups
_emailValidator = new EmailValidator();
_emailValidatables = new Validatables(RecipientName, EmailAddress);
// maybe even set some defaults
RecipientName.Value = "Fred Fredovich";
}
public OverallValidationResult Validate(Email email)
{
return _emailValidator.Validate(email).ApplyResultsTo(_emailValidatables);
}
public void ClearValidation(string clearOptions = "")
{
_emailValidatables.Clear(clearOptions);
}
实施命令（以下示例使用 Prism 的 DelegateCommand，但显然这不是必需的）以使用这些方法：
private DelegateCommand<string> _clearValidationCommand;
private DelegateCommand _validateEmailCommand;
public DelegateCommand<string> ClearValidationCommand =>
_clearValidationCommand ?? (_clearValidationCommand = new DelegateCommand<string>(ClearValidation)); // already defined above in step 4 as part of the interface requirements
public DelegateCommand ValidateEmailCommand =>
_validateEmailCommand ?? (_validateEmailCommand = new DelegateCommand(ExecuteValidateEmailCommand));
public void ExecuteValidateEmailCommand()
{
var email = _emailValidatables.Populate<Email>(); // this conveniently creates a new Email instance with the values from our Validatable objects (populated by the user via the View)
var overallValidationResult = Validate(email); // remember, this will also populate each individual Validatable's IsValid status and Errors list.
if (overallValidationResult.IsValidOverall)
{
// do something with the validated email instance
}
else
{
// do something else
}
if (overallValidationResult.NonSplitErrors.Any())
{
// do something with errors that don't pertain to any of our Validatables (which is not possible in our little example here)
}
}
最后，视图（在本例中为 XAML）：
<Entry
Placeholder="Email"
Text="{Binding EmailAddress.Value}">
<Entry.Behaviors>
<!-- Note this behavior is included in the Prism Library -->
<behaviors:EventToCommandBehavior
Command="{Binding ClearValidationCommand}"
CommandParameter="RecipientEmailAddress"
EventName="Focused" />
</Entry.Behaviors>
</Entry>
<Label
Style="{StaticResource ErrorLabelStyle}"
Text="{Binding EmailAddress.FirstError}" />
<Button
Command="{Binding ValidateEmailCommand}"
Text="Validate" />
这可能是最常见的用例 - 我们有：
- 接受用户输入的条目（只显示 1 个而不是每个 属性
- 为简洁起见）
- 将执行验证的按钮
- 一个标签，显示条目下可能存在的许多错误中的第一个，或者 none 当然
- 如果验证成功
- 用户再次激活条目后清除验证错误标签的行为（可能是为了修复错误）
但您也可以使用一个按钮来一次清除所有验证，甚至连同实际值一起清除（清除整个表单）等 - 只需通读 [=76] 中的完整示例=] 到 repo，以及使用它的完整工作的 Xamarin 示例项目（其中包括一些更高级的示例，例如使用基于上下文的规则）。
希望这对您有所帮助...