在WPF中應(yīng)用數(shù)據(jù)綁定時(shí)經(jīng)常需要做一些簡(jiǎn)單的邏輯判斷。
比如ViewModel中有一個(gè)HasError（布爾值）的屬性表示是否有錯(cuò)誤。我需要將它綁定于Button的IsEnable屬性上，即：當(dāng)沒(méi)有錯(cuò)誤時(shí)Button可用。這時(shí)就需要將HasError取反。WPF默認(rèn)的綁定引擎是不支持的。
還有一種情況比如ViewModel中有一個(gè)Sex（int值）的屬性表示性別，我需要將它綁定到TextBlock上，當(dāng)值為1時(shí)顯示男，值為2時(shí)顯示女。WPF默認(rèn)綁定也是不支持這種判斷的。
于是一個(gè)通用的值轉(zhuǎn)換器就誕生了，用法如下：
<Button IsEnabled="{Binding HasError, Converter={StaticResource GenericTypeConverter}, ConverterParameter='IsReverse=True'}">OK</Button>
IsReverse參數(shù)表示是否取返，如果轉(zhuǎn)換的值為true則變?yōu)閒alse，反之亦然。
<TextBlock Text="{Binding Sex, Converter={StaticResource GenericTypeConverter}, ConverterParameter='Alias=1:男|2:女|other:未知'}" />
Alias參數(shù)表示將值映射為字符串，other表示當(dāng)遇到?jīng)]有指定的值時(shí)顯示的文本
另外bool to Visibility的轉(zhuǎn)換可以自動(dòng)進(jìn)行，不需要指定參數(shù)。
有意見歡迎指正
完整代碼如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Data;
using System.Windows;
namespace MoodSunshiny.WPF.Converter
{
/// <summary>
/// 一個(gè)通用的類型轉(zhuǎn)換器，可以提供更多轉(zhuǎn)換控制參數(shù)
/// </summary>
public class GenericTypeConverter : IValueConverter
{
/// <summary>
/// 是否反轉(zhuǎn)轉(zhuǎn)換源參數(shù)值
/// 僅對(duì)bool類型的值有效
/// </summary>
private bool IsReverse { get; set; }
/// <summary>
/// 用于將轉(zhuǎn)換結(jié)果映射為其它字符串
/// 例如：Alias=True:是|False:否
/// </summary>
private Dictionary<object, string> Alias { get; set; }
/// <summary>
/// 解析轉(zhuǎn)換參數(shù)
/// </summary>
private void AnalyseConvertParameter(string convertParameter)
{
/*設(shè)置參數(shù)默認(rèn)值*/
IsReverse = false;
Alias = null;
if (!string.IsNullOrEmpty(convertParameter))
{
var pkvs = convertParameter.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
foreach (var pkv in pkvs)
{
var pkvo = pkv.Split(new char[] { '=' }, StringSplitOptions.RemoveEmptyEntries);
if (pkvo.Length != 2)
throw new NotSupportedException("不支持設(shè)置：" + pkv);
var pk = pkvo[0].Trim();
var pv = pkvo[1].Trim();
switch (pk)
{
case "IsReverse":
bool b;
if (!bool.TryParse(pv, out b))
throw new NotSupportedException("參數(shù)取值錯(cuò)誤：" + pkv);
else
IsReverse = b;
break;
case "Alias":
{
Alias = new Dictionary<object, string>();
var dfkvs = pv.Split(new char[] { '|' }, StringSplitOptions.RemoveEmptyEntries);
foreach (var dfkv in dfkvs)
{
var dfkvo = dfkv.Split(new char[] { ':' }, StringSplitOptions.RemoveEmptyEntries);
if (dfkvo.Length != 2)
throw new NotSupportedException("不支持設(shè)置：" + dfkvo);
var dfk = dfkvo[0].Trim();
var dfv = dfkvo[1].Trim();
object oKey = null;
int i;
if (dfk.Equals("true", StringComparison.OrdinalIgnoreCase))
oKey = true;
else if (dfk.Equals("false", StringComparison.OrdinalIgnoreCase))
oKey = false;
else if (dfk.Equals("other", StringComparison.OrdinalIgnoreCase))
oKey = "other";
else if (int.TryParse(dfk, out i))
oKey = i;
else
throw new NotSupportedException("參數(shù)取值錯(cuò)誤：" + dfkv);
Alias[oKey] = dfv;
}
}
break;
default:
throw new NotSupportedException("不支持的參數(shù)名：" + pk);
}
}
}
}
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
AnalyseConvertParameter(parameter as string);
try
{
var sourceType = value.GetType();
if (IsReverse && sourceType == typeof(bool))
value = !((bool)value);
if (targetType == typeof(string))
{
if (Alias != null && Alias.ContainsKey(value))
return Alias[value];
else if (Alias != null && Alias.ContainsKey("other"))
return Alias["other"];
else
return value == null ? "" : value.ToString();
}
if (targetType == typeof(bool))
{
if (sourceType == typeof(Visibility))
return (Visibility)value == Visibility.Visible;
}
else if (targetType.IsEnum)
{
if (sourceType == typeof(bool) && targetType == typeof(Visibility))
{
return (bool)value ? Visibility.Visible : Visibility.Collapsed;
}
else
{
return Enum.Parse(targetType, value.ToString(), true);
}
}
else
{
return System.Convert.ChangeType(value, targetType);
}
return System.Convert.ChangeType(value, targetType);
}
catch
{
return null;
}
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return Convert(value, targetType, parameter, culture);
}
}
}
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