WPF词典绑定失败是很慢 [英] WPF Dictionary Binding failure is very slow

问题描述

我有大部分的标签在我的应用程序对象的约束，这样它们可以从Web服务所取代。

I have most of the Label objects in my app bound such that they can be replaced from a webservice.

我存储我更换了字典。这些替代的基础上加载的应用程序客户端而有所不同。

I store my replacements in a Dictionary. The replacements vary based on the Client that loaded for the app.

我遇到的问题是，大部分的时候我不用更换标签，并绑定失败抛出异常，这是非常缓慢的。

The problem I am having is that most of the time I don't replace the labels, and the binding failure is throwing an exception that is very slow.

下面是一个例子：（正确地注意这个code函数，它仅仅是缓慢的，如果它不能找到匹配）的

<Label Content="_Gender"
       Helpers:CaptionHelper.PropertyName="Content"
       Helpers:CaptionHelper.PropertyValue="{Binding Labels[Gender], 
                                                     FallbackValue=_Gender}"
       Target="{Binding ElementName=cbGender}" />

在结合试图查询标贴[两性]，我得到这个在我的输出窗口：

When the binding tries to lookup Lables[Gender], I get this in my output window:

System.Windows.Data Warning: 17 : Cannot get 'Item[]' value (type 'String') from 'Labels' (type 'Dictionary`2'). BindingExpression:Path=Labels[Gender]; DataItem='MyViewMV'
      (HashCode=63776763); target element is 'Label' (Name=''); target property is 'PropertyValue'(type 'String') TargetInvocationException:'System.Reflection.TargetInvocationException: 
           Exception has been thrown by the target of an invocation. ---> System.Collections.Generic.KeyNotFoundException: 
           The given key was not present in the dictionary.
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle._InvokeMethodFast(Params Truncated)
   at System.Reflection.RuntimeMethodInfo.Invoke(Params Truncated)
   at System.Reflection.RuntimeMethodInfo.Invoke(Params Truncated)
   at MS.Internal.Data.PropertyPathWorker.GetValue(Params Truncated)
   at MS.Internal.Data.PropertyPathWorker.RawValue(Params Truncated)'

因为我有很多这样的，它走约一整秒，通过它们来运行。

Since I have a lot of these, it is taking about a full second to run through them all.

有没有一种方法，使绑定不是抛出一个异常，当字典查找失败？或者以某种方式失败更快？

Is there a way to make the binding not throw an exception when the dictionary look up fails? Or somehow fail quicker?

推荐答案

如果你有选择，我会改变你的的IDictionary 实施一个返回空，而使用 TargetNullValue （或者甚至是的IDictionary＆LT; TKEY的，对象＆gt; 并返回 DependencyProperty.UnsetValue 如果你还在用 FallbackValue ）：

If you have the option to, I would change your IDictionary implementation to one that returns null and instead use TargetNullValue (or even be IDictionary<TKey, object> and return DependencyProperty.UnsetValue if you still use FallbackValue):

public class PassthruDictionary<TKey, TValue> : IDictionary<TKey, TValue>
{
    private Dictionary<TKey, TValue> instance;

    // ... other stuff

    public TValue this[TKey key]
    {
        get
        {
            TValue value;
            if (instance.TryGetValue(key, out value))
            {
                return value;
            }
            else
            {
                return default(TValue);
            }
        }
        // ... more
    }
}

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