此示例演示了如何使用具有 IPropertyBagVisitor 和 IPropertyVisitor 接口的低级 API 来创建属性访问者。此示例等同于使用 PropertyVisitor 基类创建属性访问者的示例。
此示例包含创建属性访问程序的分步说明，此访问程序将对象的当前状态打印到控制台。
假设您具有以下类型：
public class Data
{
public string Name = "Henry";
public Vector2 Vec2 = Vector2.one;
public List<Color> Colors = new List<Color> { Color.green, Color.red };
public Dictionary<int, string> Dict = new Dictionary<int, string> {{5, "zero"}};
}
创建如下所示的实用程序方法 DebugUtilities：
public static class DebugUtilities
{
public static void PrintObjectDump<T>(T value)
{
// Magic goes here.
}
}
使用 Data 对象调用 PrintObjectDump 方法，如下所示：
DebugUtilities.PrintObjectDump(new Data());
将以下内容打印到控制台：
- Name {string} = Henry
- Vec2 {Vector2} = (1.00, 1.00)
- Colors {List<Color>}
- [0] = {Color} RGBA(0.000, 1.000, 0.000, 1.000)
- [1] = {Color} RGBA(1.000, 0.000, 0.000, 1.000)
- Dict {Dictionary<int, string>}
- [5] {KeyValuePair<int, string>}
- Key {int} = 5
- Value {string} = five
首先，创建一个实现 IPropertyBagVisitor 的 DumpObjectVisitor 类。在类中，使用 StringBuilder 构建表示对象当前状态的字符串。
创建一个实现 IPropertyBagVisitor 接口的 DumpObjectVisitor 类。
向该类添加 StringBuilder 字段。
添加一个 Reset 方法，用于清除 StringBuilder 并重置缩进级别。
添加一个 GetDump 方法，返回对象当前状态的字符串表示。
DumpObjectVisitor 类如下所示：
public class DumpObjectVisitor
: IPropertyBagVisitor
, IPropertyVisitor
{
private const int k_InitialIndent = 0;
private readonly StringBuilder m_Builder = new StringBuilder();
private int m_IndentLevel = k_InitialIndent;
public void Reset()
{
m_Builder.Clear();
m_IndentLevel = k_InitialIndent;
}
public string GetDump()
{
return m_Builder.ToString();
}
}
在 DumpObjectVisitor 类中，覆盖 IPropertyBagVisitor.Visit 方法以循环访问容器对象的属性。在对象转储访问者中，显示值并将访问委托给属性。
要使用 this 对属性调用 Accept 方法，请实现 IPropertyVisitor 接口。此接口可用于在访问属性时指定访问行为，类似于 PropertyVisitor 类的 VisitProperty 方法。
在 DumpObjectVisitor 类中，添加覆盖 IPropertyBagVisitor.Visit 和 IPropertyVisitor.Visit 方法。
void IPropertyBagVisitor.Visit<TContainer>(IPropertyBag<TContainer> propertyBag, ref TContainer container)
{
foreach (var property in propertyBag.GetProperties(ref container))
{
property.Accept(this, ref container);
}
}
void IPropertyVisitor.Visit<TContainer, TValue>(Property<TContainer, TValue> property, ref TContainer container)
{
var value = property.GetValue(ref container);
// Code goes here.
}
与 PropertyVisitor 基类一起使用的 IVisitPropertyAdapter 适配器需要访问访问者的内部状态，因此不能在该类之外使用它们。但是，可以定义具有必要信息的特定域的适配器。在 DumpObjectVisito 类中，更新 IPropertyVisitor 的实现以首先使用适配器：
// Create the following methods to encapsulate the formatting of the message and display the value.
public readonly struct PrintContext
{
private StringBuilder Builder { get; }
private string Prefix { get; }
public string PropertyName { get; }
public void Print<T>(T value)
{
Builder.AppendLine($"{Prefix}- {PropertyName} = {{{TypeUtility.GetTypeDisplayName(value?.GetType() ?? typeof(T))}}} {value}");
}
public void Print(Type type, string value)
{
Builder.AppendLine($"{Prefix}- {PropertyName} = {{{TypeUtility.GetTypeDisplayName(type)}}} {value}");
}
public PrintContext(StringBuilder builder, string prefix, string propertyName)
{
Builder = builder;
Prefix = prefix;
PropertyName = propertyName;
}
}
public interface IPrintValue
{
}
public interface IPrintValue<in T> : IPrintValue
{
void PrintValue(in PrintContext context, T value);
}
public class DumpObjectVisitor
: IPropertyBagVisitor
, IPropertyVisitor
, IPrintValue<Vector2>
, IPrintValue<Color>
{
public IPrintValue Adapter { get; set; }
public DumpObjectVisitor()
{
// For simplicity
Adapter = this;
}
void IPropertyVisitor.Visit<TContainer, TValue>(Property<TContainer, TValue> property, ref TContainer container)
{
// Here, we need to manually extract the value.
var value = property.GetValue(ref container);
var propertyName = GetPropertyName(property);
// We can still use adapters, but we must manually dispatch the calls.
if (Adapter is IPrintValue<TValue> adapter)
{
var context = new PrintContext(m_Builder, Indent, propertyName);
adapter.PrintValue(context, value);
return;
}
// Fallback behaviour here
}
void IPrintValue<Vector2>.PrintValue(in PrintContext context, Vector2 value)
{
context.Print(value);
}
void IPrintValue<Color>.PrintValue(in PrintContext context, Color value)
{
const string format = "F3";
var formatProvider = CultureInfo.InvariantCulture.NumberFormat;
context.Print(typeof(Color), $"RGBA({value.r.ToString(format, formatProvider)}, {value.g.ToString(format, formatProvider)}, {value.b.ToString(format, formatProvider)}, {value.a.ToString(format, formatProvider)})");
}
}
完成的代码如下所示：
public readonly struct PrintContext
{
// A context struct to hold information about how to print the property
private StringBuilder Builder { get; }
private string Prefix { get; }
public string PropertyName { get; }
// Method to print the value of type T with its associated property name
public void Print<T>(T value)
{
Builder.AppendLine($"{Prefix}- {PropertyName} = {{{TypeUtility.GetTypeDisplayName(value?.GetType() ?? typeof(T))}}} {value}");
}
// Method to print the value with a specified type and its associated property name
public void Print(Type type, string value)
{
Builder.AppendLine($"{Prefix}- {PropertyName} = {{{TypeUtility.GetTypeDisplayName(type)}}} {value}");
}
// Constructor to initialize the PrintContext
public PrintContext(StringBuilder builder, string prefix, string propertyName)
{
Builder = builder;
Prefix = prefix;
PropertyName = propertyName;
}
}
// Generic interface IPrintValue that acts as a marker interface for all print value adapters
public interface IPrintValue
{
}
// Generic interface IPrintValue<T> to define how to print values of type T
// This interface is used as an adapter for specific types (Vector2 and Color in this case)
public interface IPrintValue<in T> : IPrintValue
{
void PrintValue(in PrintContext context, T value);
}
// DumpObjectVisitor class that implements various interfaces for property visiting and value printing
private class DumpObjectVisitor : IPropertyBagVisitor, IPropertyVisitor, IPrintValue<Vector2>, IPrintValue<Color>
{
// (Other members are omitted for brevity)
public IPrintValue Adapter { get; set; }
public DumpObjectVisitor()
{
// The Adapter property is set to this instance of DumpObjectVisitor
// This means the current DumpObjectVisitor can be used as a print value adapter for Vector2 and Color.
Adapter = this;
}
// This method is called when visiting a property bag (a collection of properties)
void IPropertyBagVisitor.Visit<TContainer>(IPropertyBag<TContainer> propertyBag, ref TContainer container)
{
foreach (var property in propertyBag.GetProperties(ref container))
{
// Call the Visit method of IPropertyVisitor to handle individual properties
property.Accept(this, ref container);
}
}
// This method is called when visiting each individual property of an object.
// It tries to find a suitable adapter (IPrintValue<T>) for the property value type (TValue) and uses it to print the value.
// If no suitable adapter is found, it falls back to displaying the value using its type name.
void IPropertyVisitor.Visit<TContainer, TValue>(Property<TContainer, TValue> property, ref TContainer container)
{
// Here, we need to manually extract the value.
var value = property.GetValue(ref container);
var propertyName = GetPropertyName(property);
// We can still use adapters, but we must manually dispatch the calls.
// Try to find an adapter for the current property value type (TValue).
if (Adapter is IPrintValue<TValue> adapter)
{
// If an adapter is found, create a print context and call the PrintValue method of the adapter.
var context = new PrintContext(m_Builder, Indent, propertyName);
adapter.PrintValue(context, value);
return;
}
// Fallback behavior here - if no adapter is found, handle printing based on type information.
var type = value?.GetType() ?? property.DeclaredValueType();
var typeName = TypeUtility.GetTypeDisplayName(type);
if (TypeTraits.IsContainer(type))
m_Builder.AppendLine($"{Indent}- {propertyName} {{{typeName}}}");
else
m_Builder.AppendLine($"{Indent}- {propertyName} = {{{typeName}}} {value}");
// Recursively visit child properties (if any).
++m_IndentLevel;
if (null != value)
PropertyContainer.Accept(this, ref value);
--m_IndentLevel;
}
// Method from IPrintValue<Vector2> used to print Vector2 values
void IPrintValue<Vector2>.PrintValue(in PrintContext context, Vector2 value)
{
// Simply use the Print method of PrintContext to print the Vector2 value.
context.Print(value);
}
// Method from IPrintValue<Color> used to print Color values
void IPrintValue<Color>.PrintValue(in PrintContext context, Color value)
{
const string format = "F3";
var formatProvider = CultureInfo.InvariantCulture.NumberFormat;
// Format and print the Color value in RGBA format.
context.Print(typeof(Color), $"RGBA({value.r.ToString(format, formatProvider)}, {value.g.ToString(format, formatProvider)}, {value.b.ToString(format, formatProvider)}, {value.a.ToString(format, formatProvider)})");
}
}
对数据运行访问程序时，默认情况下，它会直接在给定的对象上开始访问。对于任何属性访问程序，要开始访问对象的子属性，请将 PropertyPath 传递给 PropertyContainer.Accept 方法。
更新 DebugUtilities 方法以采取可选的 PropertyPath：
public static class DebugUtilities
{
private static readonly DumpObjectVisitor s_Visitor = new();
public static void PrintObjectDump<T>(T value, PropertyPath path = default)
{
s_Visitor.Reset();
if (path.IsEmpty)
PropertyContainer.Accept(s_Visitor, ref value);
else
PropertyContainer.Accept(s_Visitor, ref value, path);
Debug.Log(s_Visitor.GetDump());
}
}
使用 Data 对象调用 PrintObjectDump 方法。这将获得所需输出。