IRuleExpression 介面

定義

命名空間:

System.Workflow.Activities.Rules

組件:

System.Workflow.Activities.dll

表示基底類別 (Base Class)，自訂運算式寫入器必須衍生自此基底類別，才能寫入自訂運算式。

public interface class IRuleExpression

public interface IRuleExpression

type IRuleExpression = interface

Public Interface IRuleExpression

範例

下列程式碼會建立一個運算式，該運算式可用於宣告式條件和規則集。 該運算式是已命名的 TwoOfThree，並採用 3 個參數，這 3 個參數全都必須評估為布林值。 如果 3 個運算式中有 2 個傳回 true，則這個運算式會傳回 true。

若要使用這個程式碼，請將它加入類別庫 (Class Library) 專案，並參考工作流程專案中的程式庫。

using System.CodeDom;  
using System.Text;  
using System.Workflow.Activities.Rules;  
using System.Workflow.ComponentModel.Compiler;  

namespace TwoOfThreeRuleExpression  
{  
    public class TwoOfThree : CodeExpression, IRuleExpression  
    {  
        CodeExpression expression1, expression2, expression3;  

        public CodeExpression First  
        {  
            get { return expression1; }  
            set { expression1 = value; }  
        }  

        public CodeExpression Second  
        {  
            get { return expression2; }  
            set { expression2 = value; }  
        }  

        public CodeExpression Third  
        {  
            get { return expression3; }  
            set { expression3 = value; }  
        }  

        public TwoOfThree()  
        {  
            // constructor required for deserialization  
        }  

        public TwoOfThree(CodeExpression first, CodeExpression second, CodeExpression third)  
        {  
            // constructor required by parser  
            expression1 = first;  
            expression2 = second;  
            expression3 = third;  
        }  

        public void AnalyzeUsage(RuleAnalysis analysis, bool isRead, bool isWritten, RulePathQualifier qualifier)  
        {  
            // check what the 3 expressions use  
            RuleExpressionWalker.AnalyzeUsage(analysis, expression1, true, false, null);  
            RuleExpressionWalker.AnalyzeUsage(analysis, expression2, true, false, null);  
            RuleExpressionWalker.AnalyzeUsage(analysis, expression3, true, false, null);  
        }  

        public CodeExpression Clone()  
        {  
            TwoOfThree result = new TwoOfThree();  
            result.expression1 = RuleExpressionWalker.Clone(expression1);  
            result.expression2 = RuleExpressionWalker.Clone(expression2);  
            result.expression3 = RuleExpressionWalker.Clone(expression3);  
            return result;  
        }  

        public void Decompile(StringBuilder stringBuilder, CodeExpression parentExpression)  
        {  
            // what should be displayed by the parser  
            stringBuilder.Append("TwoOfThree(");  
            RuleExpressionWalker.Decompile(stringBuilder, expression1, this);  
            stringBuilder.Append(", ");  
            RuleExpressionWalker.Decompile(stringBuilder, expression2, this);  
            stringBuilder.Append(", ");  
            RuleExpressionWalker.Decompile(stringBuilder, expression3, this);  
            stringBuilder.Append(")");  
        }  

        static RuleLiteralResult resultTrue = new RuleLiteralResult(true);  
        static RuleLiteralResult resultFalse = new RuleLiteralResult(false);  

        public RuleExpressionResult Evaluate(RuleExecution execution)  
        {  
            // start by doing the first 2 expressions  
            RuleExpressionResult r1 = RuleExpressionWalker.Evaluate(execution, expression1);  
            RuleExpressionResult r2 = RuleExpressionWalker.Evaluate(execution, expression2);  
            bool b1 = (bool)r1.Value;  
            bool b2 = (bool)r2.Value;  
            if (b1 && b2)  
            {  
                // both are true, so result is true  
                return resultTrue;  
            }  
            else if (b1 || b2)  
            {  
                // only one of the first 2 is true, evaluate the third to determine result  
                return RuleExpressionWalker.Evaluate(execution, expression3);  
            }  
            else  
                // both e1 and e2 are false, so skip e3 and return false;  
                return resultFalse;  
        }  

        public bool Match(CodeExpression expression)  
        {  
            TwoOfThree other = expression as TwoOfThree;  
            return (other != null) &&  
                RuleExpressionWalker.Match(expression1, other.expression1) &&  
                RuleExpressionWalker.Match(expression2, other.expression2) &&  
                RuleExpressionWalker.Match(expression3, other.expression3);  
        }  

        public RuleExpressionInfo Validate(RuleValidation validation, bool isWritten)  
        {  
            ValidateExpression(validation, expression1, "First");  
            ValidateExpression(validation, expression2, "Second");  
            ValidateExpression(validation, expression3, "Third");  
            return new RuleExpressionInfo(typeof(bool));  
        }  

        private void ValidateExpression(RuleValidation validation, CodeExpression expression, string propertyName)  
        {  
            ValidationError error;  
            if (expression == null)  
            {  
                error = new ValidationError(propertyName + " cannot be null", 123);  
                validation.Errors.Add(error);  
            }  
            else  
            {  
                RuleExpressionInfo result = RuleExpressionWalker.Validate(validation, expression, false);  
                if ((result == null) || (result.ExpressionType != typeof(bool)))  
                {  
                    error = new ValidationError(propertyName + " must return boolean result", 123);  
                    validation.Errors.Add(error);  
                }  
            }  
        }  
    }  
}  

方法

AnalyzeUsage(RuleAnalysis, Boolean, Boolean, RulePathQualifier)	在衍生類別中覆寫時，報告物件如何使用內容型別中的欄位和屬性。
Clone()	在衍生類別中覆寫時，建立目前 CodeExpression 的深層複本。
Decompile(StringBuilder, CodeExpression)	在衍生類別中複寫時，將自訂運算式反編譯成字串格式。
Evaluate(RuleExecution)	在衍生類別中覆寫時，評估自訂運算式。
Match(CodeExpression)	將目前運算式與其他運算式比較，判斷這兩個運算式是否相等。
Validate(RuleValidation, Boolean)	在衍生類別中覆寫時，會驗證運算式已正確設定，而且沒有任何錯誤。