如何将图像添加到电子邮件行为

Question

我想知道如何将image 添加到行为中，实际上我正在尝试编写能够更改条目背景的电子邮件行为，但同时我想为其添加图像。

我的xml：

<StackLayout>
      <Entry Placeholder="Enter a System.Double">
          <Entry.Behaviors>
              <local:CustomBehavior />
          </Entry.Behaviors>
      </Entry>
</StackLayout> 

我的行为类：

public class CustomBehavior: Behavior<Entry>
{
    private const string digitRegex = @"^(?("")("".+?(?<!\\)""@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])@))" +
            @"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9][\-a-z0-9]{0,22}[a-z0-9]))$";

    protected override void OnAttachedTo(Entry entry)
    {
        entry.TextChanged += OnEntryTextChanged;
        base.OnAttachedTo(entry);
    }

    protected override void OnDetachingFrom(Entry entry)
    {
        entry.TextChanged -= OnEntryTextChanged;
        base.OnDetachingFrom(entry);
    }

    void OnEntryTextChanged(object sender, TextChangedEventArgs e)
    {
        Entry entry;
        bool isValid;
        entry =(Entry)sender;
        isValid = Regex.IsMatch(e.NewTextValue, digitRegex);
        entry.BackgroundColor = isValid ? Color.Default : Color.Red;
    }
}

Answer 1

第一个。根据您的要求，您必须在布局中添加单独的图片：

<StackLayout
      Orientation="Horizontal">
      <Entry Placeholder="Enter a System.Double">
          <Entry.Behaviors>
              <local:CustomBehavior x:Name="customValidator"/>
          </Entry.Behaviors>
      </Entry>
      <Image
          HeightRequest="24"
          WidthRequest="24"
          Aspect="AspectFit"
          IsVisible="{Binding Source={x:Reference customValidator},
                        Path=IsVisible}"
          Style="{Binding Source={x:Reference customValidator},
                        Path=IsValid,
                        Converter={StaticResource boolToStyleImage}}"/>
</StackLayout> 

注意 x:Name="" 属性，因为这是在此 xaml 文件中引用该自定义行为所必需的

第二次。在您的“CustomBehavior”上为两个字段创建 BindableProperties，您将在这两个字段上绑定您的条目的图像状态

public class CustomBehavior: Behavior<Entry>
{
    private const string digitRegex = @"^(?("")("".+?(?<!\\)""@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])@))" +
        @"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9][\-a-z0-9]{0,22}[a-z0-9]))$";

    static readonly BindablePropertyKey IsValidPropertyKey = BindableProperty.CreateReadOnly ("IsValid", typeof (bool), typeof (CustomBehavior), false);
    public static readonly BindableProperty IsValidProperty = IsValidPropertyKey.BindableProperty;

    static readonly BindablePropertyKey IsVisiblePropertyKey = BindableProperty.CreateReadOnly ("IsVisible", typeof (bool), typeof (CustomBehavior), false);
    public static readonly BindableProperty IsVisibleProperty = IsVisiblePropertyKey.BindableProperty;

    private const string FRIEND = "friend";
    private const string FRIENDS = "friends";

    public bool IsValid
    {
        get { return (bool)base.GetValue (IsValidProperty); }
        private set { base.SetValue (IsValidPropertyKey, value); }
    }

    public bool IsVisible
    {
        get { return (bool)base.GetValue (IsVisibleProperty); }
        private set { base.SetValue (IsVisiblePropertyKey, value); }
    }

    protected override void OnAttachedTo(Entry entry)
    {
        entry.TextChanged += OnEntryTextChanged;
        base.OnAttachedTo(entry);
    }

    protected override void OnDetachingFrom(Entry entry)
    {
        entry.TextChanged -= OnEntryTextChanged;
        base.OnDetachingFrom(entry);
    }

    void OnEntryTextChanged(object sender, TextChangedEventArgs e)
    {
        if (e.NewTextValue.Length > 0)
        {
            IsVisible = true;
            Entry entry =(Entry)sender;
            IsValid = Regex.IsMatch(e.NewTextValue, digitRegex);

            if(IsValid) // Check only if we have a valid email
            {
                // Here we validate if the email contains our requirements
                String email = entry.Text;
                int pos = email.IndexOf("@"); // Exclude the domain
                string username = email.Substring(0, pos);
                if(username.Contains(FRIEND) || username.Contains(FRIENDS))
                {
                    IsValid = true;
                }else
                    IsValid = false;
                }
            }
        }else
            IsVisible = false;
    }
}

3d。创建一个简单的 ValueConverter 类，它将一个布尔值转换为我们的“T”类型的对象之一，具体取决于我们将此转换器附加到的对象。

namespace YourApp
public class BooleanToObjectConverter<T> : IValueConverter
{
    public T FalseObject { set; get; }

    public T TrueObject { set; get; }

    public object Convert (object value, Type targetType,
                          object parameter, CultureInfo culture)
    {
        return (bool)value ? this.TrueObject : this.FalseObject;
    }

    public object ConvertBack (object value, Type targetType,
                              object parameter, CultureInfo culture)
    {
        return ((T)value).Equals (this.TrueObject);
    }
}

4th. 将此样式添加到 App.xaml 文件的 ResourceDictionary 标记中，这将声明 TrueObject（有效电子邮件的样式）和 FalseObject（无效电子邮件的样式）。

将“your_wrong_image_here.png”和“your_correct_image_here.png”替换为您想要的图片

<Application 
    xmlns="http://xamarin.com/schemas/2014/forms" 
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
    x:Class="YourApp.App"
    xmlns:statics="clr-namespace:YourApp">
    <Application.Resources>
        <!-- Application resource dictionary -->
        <ResourceDictionary>
        <statics:BooleanToObjectConverter x:Key="boolToStyleImage" 
x:TypeArguments="Style">
            <statics:BooleanToObjectConverter.FalseObject>
                <Style TargetType="Image">
                    <Setter Property="HeightRequest" Value="24" />
                    <Setter Property="Source" 
Value="your_wrong_image_here.png" />
                </Style>
            </statics:BooleanToObjectConverter.FalseObject>

            <statics:BooleanToObjectConverter.TrueObject>
                <Style TargetType="Image">
                    <Setter Property="HeightRequest" Value="24" />
                    <Setter Property="Source" 
Value="your_correct_image_here.png" />
                </Style>
            </statics:BooleanToObjectConverter.TrueObject>
       </statics:BooleanToObjectConverter>
       </ResourceDictionary>
    </Application.Resources>
</Application>

这应该可以满足您的需求，只是要小心复制粘贴错误，因为您的项目中有不同的类名！