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私は、文字列値の配列を単一の文字列オブジェクトに変換する簡単なコンバーターを持っています。つまり、区切り文字を使用してすべての文字列を結合します。アプリケーションが実行されると、値コンバータのブレークポイントにヒットします。これは、連結された文字列をラベルに期待通りに表示していません。値のコンバーターが動作しない
ビュー：背後に
<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="mvvm.Views.LoginPage"
xmlns:converters="clr-namespace:XFApp.Core.Converters;assembly=XFApp.Core">
<ContentPage.Resources>
<ResourceDictionary>
<converters:ValidationErrorConverter x:Key="validationErrorConverter" />
</ResourceDictionary>
</ContentPage.Resources>
<StackLayout Padding="10,100,10,10">
<StackLayout>
<Label
Text="{Binding Errors, Converter={StaticResource validationErrorConverter}}" />
<Label Text="User name:" />
<Entry x:Name="entryUsername" Keyboard="Email" Text="{Binding Username, Mode=TwoWay}" Style="{StaticResource EntryStyle}" />
<Label Text="Password:" />
<Entry x:Name="entryPassword" IsPassword="true" Text="{Binding Password, Mode=TwoWay}" Style="{StaticResource EntryStyle}" />
</StackLayout>
<Button VerticalOptions="EndAndExpand" Text="LOGIN" Command="{Binding AuthenticateUserCommand}" />
</StackLayout>
</ContentPage>
コードの表示：
using mvvm.ViewModels;
using Xamarin.Forms;
namespace mvvm.Views
{
public partial class LoginPage : ContentPage
{
LoginViewModel viewModel = new LoginViewModel();
public LoginPage()
{
InitializeComponent();
this.BindingContext = viewModel;
}
}
}
のViewModel：
using System.Windows.Input;
using Xamarin.Forms;
using mvvm.Models;
using System.Collections.Generic;
using XFApp.Core.ViewModels;
namespace mvvm.ViewModels
{
public class LoginViewModel : ViewModelBase
{
private string _username;
private string _password;
private bool _isValid;
private IList<string> _errors;
public LoginViewModel()
{
_username = "";
_password = "";
_errors = new List<string>();
}
public IList<string> Errors
{
set { SetProperty(ref _errors, value); }
get { return _errors; }
}
public string Username {
set {
SetProperty(ref _username, value);
((Command)AuthenticateUserCommand).ChangeCanExecute();
}
get { return _username; }
}
public string Password
{
set {
SetProperty(ref _password, value);
((Command)AuthenticateUserCommand).ChangeCanExecute();
}
get { return _password; }
}
public bool IsValid
{
set { SetProperty(ref _isValid, value); }
get { return _isValid; }
}
public ICommand AuthenticateUserCommand => new Command(
execute:() => {
AuthenticateUserAsync();
}
//,
//canExecute:() => {
// return (Username.Length > 0);
//}
);
private bool Validate()
{
if (_username == "")
{
_errors.Add("An e-mail address is required.");
Errors = _errors;
}
if (_password == "")
{
_errors.Add("A password is required.");
Errors = _errors;
}
return _errors.Count == 0;
}
private async void AuthenticateUserAsync()
{
Errors.Clear();
IsValid = true;
bool isValid = Validate();
bool isAuthenticated = false;
Token token = null;
if (!isValid)
{
IsValid = false;
return;
}
token = await Services.UserService.IsValidUser(_username, _password);
if (token != null)
isAuthenticated = true;
if (isAuthenticated)
{
//new Messenger().Subscribe<LoginFailedMessage>(this, loginPage.LoginFailed);
//MainPage = new NavigationPage(new mvvmPage());
}
else
{
//Errors.Clear();
//Errors.Add("Invalid credentials.");
}
}
}
}
コンバータ：
using System;
using System.Collections.Generic;
using System.Globalization;
using Xamarin.Forms;
namespace XFApp.Core.Converters
{
public class ValidationErrorConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
List<string> errors = value as List<string>;
return errors != null && errors.Count > 0 ? string.Join("\r\n", errors.ToArray()) : "";
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
ViewModelBase：私はオブジェクトの一覧を表示するために関連するビューモデルのコードにいくつかの変更を行った後
using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
namespace XFApp.Core.ViewModels
{
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected bool SetProperty<T>(ref T storage, T value,
[CallerMemberName] string propertyName = null)
{
if (Object.Equals(storage, value))
return false;
storage = value;
OnPropertyChanged(propertyName);
return true;
}
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
}