[英]Can I cast generic type to Dictionary<,> in C#?
我在某些词典集合中有程序设置。
而且我需要通过配置文件( dst字典)中的设置来更新默认设置( src字典)。
因此,我写了一个通用的扩展方法,该方法不适用于字典中的字典:
public static class DictionaryExtensions
{
public static void Update<T, U>(this Dictionary<T, U> src, Dictionary<T, U> dst)
{
// Update values by keys
var keys = src.Select(x => x.Key).ToArray();
foreach (var key in keys)
if (dst.ContainsKey(key))
{
if (typeof(U).GetGenericTypeDefinition() == typeof(Dictionary<,>))
{ // Error in recursively calling:
var d1 = src[key] as Dictionary<object, object>; // d1 is null, but it is Dictionary<,>
var d2 = dst[key] as Dictionary<object, object>; // d2 is null, but it is Dictionary<,>
d1.Update(d2); // How can I call it?
}
else
src[key] = dst[key];
}
// Append not exist values
keys = dst.Select(x => x.Key).ToArray();
foreach (var key in keys)
if (!src.ContainsKey(key))
src.Add(key, dst[key]);
}
}
我可以将类U转换为Dictionary <,>的未知类型,然后递归调用Update()方法吗?
使用IDictionay,不使用通用类型,可能可以做到,我还没有尝试过
public static class DictionaryExtensions
{
public static void Update(this IDictionary src, IDictionary dst)
{
foreach (object srcKey in src.Keys)
{
foreach (object dstKey in dst.Keys)
{
if (dst.Contains(srcKey))
{
IDictionary d1 = src[srcKey] as IDictionary;
IDictionary d2 = dst[srcKey] as IDictionary;
if (d1 != null && d2 != null)
{
d1.Update(d2);
}
else
src[srcKey] = dst[srcKey];
}
}
}
foreach (object dstKey in dst.Keys)
if (!src.Contains(dstKey))
src.Add(dstKey, dst[dstKey]);
}
}
并像这样使用。
Dictionary<object, object> a = new Dictionary<object, object>();
Dictionary<object, object> b = new Dictionary<object, object>();
a.Update(b);
感谢TimChang,现在我的代码是:
public static class DictionaryExtensions
{
public static void Update(this IDictionary src, IDictionary dst)
{
foreach (var key in dst.Keys)
if (src.Contains(key))
{
if (src[key] is IDictionary a &&
dst[key] is IDictionary b)
a.Update(b);
else
src[key] = dst[key];
}
else
{
src.Add(key, dst[key]);
}
}
}
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