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using System;
using System.Collections.Generic;
using System.Reflection;
using System.Text;
namespace Google.ProtocolBuffers {
/// <summary>
/// Utilities for arbitrary messages of an unknown type. This class does not use
/// generics precisely because it is designed for dynamically discovered types.
/// </summary>
public static class MessageUtil {
/// <summary>
/// Returns the default message for the given type. If an exception is thrown
/// (directly from this code), the message will be suitable to be displayed to a user.
/// </summary>
/// <param name="type"></param>
/// <exception cref="ArgumentNullException">The type parameter is null.</exception>
/// <exception cref="ArgumentException">The type doesn't implement IMessage, or doesn't
/// have a static DefaultMessage property of the same type, or is generic or abstract.</exception>
/// <returns></returns>
public static IMessage GetDefaultMessage(Type type) {
if (type == null) {
throw new ArgumentNullException("type", "No type specified.");
}
if (type.IsAbstract || type.IsGenericTypeDefinition) {
throw new ArgumentException("Unable to get a default message for an abstract or generic type (" + type.FullName + ")");
}
if (!typeof(IMessage).IsAssignableFrom(type)) {
throw new ArgumentException("Unable to get a default message for non-message type (" + type.FullName + ")");
}
PropertyInfo property = type.GetProperty("DefaultInstance", BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic);
if (property == null) {
throw new ArgumentException(type.FullName + " doesn't have a static DefaultInstance property");
}
if (property.PropertyType != type) {
throw new ArgumentException(type.FullName + ".DefaultInstance property is of the wrong type");
}
return (IMessage) property.GetValue(null, null);
}
/// <summary>
/// Returns the default message for the type with the given name. This is just
/// a convenience wrapper around calling Type.GetType and then GetDefaultMessage.
/// If an exception is thrown, the message will be suitable to be displayed to a user.
/// </summary>
/// <param name="typeName"></param>
/// <exception cref="ArgumentNullException">The typeName parameter is null.</exception>
/// <exception cref="ArgumentException">The type doesn't implement IMessage, or doesn't
/// have a static DefaultMessage property of the same type, or can't be found.</exception>
public static IMessage GetDefaultMessage(string typeName) {
if (typeName == null) {
throw new ArgumentNullException("typeName", "No type name specified.");
}
Type type = Type.GetType(typeName);
if (type == null) {
throw new ArgumentException("Unable to load type " + typeName);
}
return GetDefaultMessage(type);
}
}
}
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