绑定Alpha Android

Question

我尝试绑定到一个ImageView阿尔法属性，我创建了一个转换器来设置布尔值。但我不认为设定的价值。

这是我的转换器

public class BooleanToOpacity : MvxValueConverter<bool,int>
{
    protected override int Convert(bool value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var boolean = value as bool?;

        if (boolean.Value == true)
        {
            return 1;
        }
        else
        {
            return 127;
        }                
    }

    protected override bool ConvertBack(int value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value > 127)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

我使用一个整数值，因为Alpha值是0到255。

这是我的行到绑定值。

   local:MvxBind="alpha TwitterPost, Converter=BooleanToOpacity" />

Mvx追踪我这个

   MvxBind:Warning: 11.56 Failed to create target binding for binding alpha for TwitterPost
   [0:] MvxBind:Warning: 11.56 Failed to create target binding for binding alpha for TwitterPost
   10-21 15:54:22.280 I/mono-stdout(12096): MvxBind:Warning: 11.56 Failed to create target binding for binding alpha for TwitterPost

有什么想法吗？

提前谢谢。

Answer 1

在C#中，"Alpha“没有可用的Xamarin.Android属性，因此Mvx框架不知道如何绑定到它。

如果您愿意，可以为此创建一个自定义绑定--比如：

    public class ImageViewAlphaTargetBinding : MvxAndroidTargetBinding
    {
        public ImageViewAlphaTargetBinding (ImageView target) : base(target)
        {
        }

        protected override void SetValueImpl(object target, object value)
        {
            var imageView = (ImageView)target;
            imageView.SetMyProperty((int)value);
        }

        public override Type TargetType
        {
            get { return typeof(int); }
        }
    }

在Setup.cs注册：

protected override void FillTargetFactories(Cirrious.MvvmCross.Binding.Bindings.Target.Construction.IMvxTargetBindingFactoryRegistry registry)
{
    registry.RegisterCustomBindingFactory<ImageView>(
                    "Alpha",
                    v=> new ImageViewAlphaTargetBinding (v) );
    base.FillTargetFactories(registry);
}

或者，您可以从ImageView继承并提供公开Alpha属性的自定义视图。

有关这两种选项的更多信息，请参见：

• 自定义绑定http://slodge.blogspot.co.uk/2013/06/n28-custom-bindings-n1-days-of-mvvmcross.html
• 继承以添加属性- http://slodge.blogspot.co.uk/2013/07/n33-animating-data-bound-text-changes.html

Answer 2

<ImageView android:layout_width="match_parent"
        android:layout_height="match_parent"
        local:MvxBind="Alpha IsImageEnable , Converter = BoolToAlpha" />


public class BoolToAlphaValueConverter : BaseValueConverter<bool, Single>
    {
        protected override Single Convert(bool value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            Single alphavalue;
            if (value)
            {
                alphavalue = 1.0f;
            }
            else {
                alphavalue = 0.35f;
            }
            return alphavalue;
        }

    }