Binding

binding之基本概念

binding之数据源和目标控件

binding 之 Data Convert

DataSource的Property和TargetControl的DependencyProperty绑定，若是两个Property的数据类型不一样，则须要转换。

bind.Convert = new DataConverter():IValueConverter
Convert属性的类型是IValueConverter

public interface IValueConverter
    {
        object Convert(object value, Type outType, object parameter, CultureInfo culture);
        object ConvertBack(object value, Type outType, object parameter, CultureInfo culture);
    }

Convert用于将数据源属性转换成目标控件属性。

value:数据源属性值
outType：转换后的数据类型
parameter:额外参数

ConvertBack用于将目标控件属性转换成数据源属性。

示例

后台数据源的SexCode，0表示女，1表示男，绑定到TextBlock。

class Sex
{
    public int SexCode { get; set; }
}
Sex sex = new Sex();
Binding bind = new Binding();
bind.Source = sex;
bind.Path = new PropertyPath("SexCode");
bind.Converter = new DataConvert();
BindingOperations.SetBinding(tbkSex, TextBlock.TextProperty, bind);
class DataConvert : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        int sexCode = (int)value;
        if(sexCode == 0)
        {
            return "女";
        }
        else
        {
            return "男";
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

示例

使用Binding的ConverterParameter的参数，使DataConvert复用，能被多个binding实例使用。

class Sex
{
    public int SexCode { get; set; }
}

class DataConvert : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        bool usage = (bool)parameter;
        if (usage)
        {
            int sexCode = (int)value;
            if (sexCode == 0)
            {
                return "女";
            }
            else if (sexCode == 1)
            {
                return "男";
            }
            else
            {
                return "保密";
            }
        }
        else
        {
            int isCoder = (int)value;
            if(isCoder == 0)
            {
                return false;
            }
            else if(isCoder == 1)
            {
                return true;
            }
            else
            {
                return null;
            }
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}
Sex sex = new Sex { SexCode = 3};
Binding bind = new Binding();
bind.Source = sex;
bind.Path = new PropertyPath("SexCode");
bind.Converter = new DataConvert();
bind.ConverterParameter = true;
BindingOperations.SetBinding(tbkSex, TextBlock.TextProperty, bind);
bind = new Binding();
bind.Source = sex;
bind.Path = new PropertyPath("SexCode");
bind.Converter = new DataConvert();
bind.ConverterParameter = false;
cbxIsCoder.SetBinding(System.Windows.Controls.Primitives.ToggleButton.IsCheckedProperty, bind);

Binding之Data Invalidation

校验是指改变目标控件的属性，会校验属性的新值，合理则更新数据源，不合理则改变控件的样式进行报错，且不更新数据源。
Binding能够有多个校验规则，一条校验规则是一个继承自抽象类的ValidationRule的类实例。Binding的属性ValidationRules,类型是Collection<ValidationRule>。继承抽象类ValidationRule实现其Validation方法，返回类型是ValidationResult，校验失败，则ValidationResult.IsValid = false;ValidationResult.ErrorContent = "错误信息"；校验成功为true和null。

public abstract class ValidationRule
{
    protected ValidationRule(ValidationStep validationStep, bool validatesOnTargetUpdated);
    public abstract ValidationResult Validate(object value, CultureInfo cultureInfo);
}
public class ValidationResult
{
    public ValidationResult(bool isValid, object errorContent);
    public static ValidationResult ValidResult { get; }
    public object ErrorContent { get; }
    public bool IsValid { get; }
}

<TextBox Width="150"
         Validation.Error="ItemError">
  <TextBox.Text>
    <Binding Source="{StaticResource myObject}"
             Path="PropertyB"
             UpdateSourceTrigger="PropertyChanged"
             NotifyOnValidationError="True">
      <Binding.ValidationRules>
        <src:ValueIsNotNull ValidatesOnTargetUpdated="True" />
      </Binding.ValidationRules>
    </Binding>
  </TextBox.Text>
</TextBox>

校验失败，咱们须要改变控件样式，来警告或提醒用户，与该状况相关的类是Invalidation。
控件有个Errors属性，类型是Collection<ValidationError>，每一个校验规则的返回值的ValidationResult的ErrorContent会填充到该集合。
Invalidation.GetErrors(目标控件)[0].ErrorContent.ToString()能拿到第一条检验失败的错误信息。

三种提醒方式

1. 发生错误时，Binding会触发Valiation.ErrorEvent路由事件，沿着目标控件在UI树上向上传播，咱们对目标控件或者UI树位置高于目标控件的控件增添路由事件，在路由事件里面，更改控件的外观属性，ToolTip，弹窗等，来提醒出错。

this.AddHandler(Validation.Error,new RoutedEventHandler(this.ErrorHandler));
或者经过XAML设置 Validation.Error = "ErrorHandler"
2.
ToolTip = "{Binding RelativeSource = {RelativeSource self},Path=(Validation.Errors)[0].ErrorContent.ToString}"
3.设置ErrorTemplate。

<Grid>
    <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
        <TextBox x:Name="textText" MinHeight="70" MinWidth="200" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Validation.Error="textText_Error">
            <TextBox.Resources>
                <local:Student Age="24" x:Key="dataSource"/>
            </TextBox.Resources>
            <TextBox.Text>
                <Binding Source="{StaticResource dataSource}" Path="Age" Mode="TwoWay" NotifyOnValidationError="True" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <local:DataInvalidation ValidatesOnTargetUpdated="True"/>
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>
    </StackPanel>
</Grid>

多路绑定