C#错误CS0201：只有赋值、调用、递增、递减和新对象表达式可以作为语句使用

Posted 2023-03-31

【中文标题】C#错误CS0201：只有赋值、调用、递增、递减和新对象表达式可以作为语句使用

【英文标题】：C# error CS0201: Only assignment, call, increment, decrement, and new object expressions can be used as a statement

【发布时间】：2013-09-13 02:38:51

【问题描述】：

这是我收到错误的行：

_activeType == typeof(Reticle);

这是Reticle 类的定义方式。有些属性和方法可能没有多大意义，但我认为类的定义应该是关键问题：

public class Reticle : Shape

    #region Fields

    private readonly Path _path;       
    private bool _isClosed;
    private PointCollection _points;       

    #endregion Fields

    #region Constructors
    public Reticle()     // constructor
    
        var geometry = new PathGeometry();
        geometry.Figures.Add(new PathFigure());
        _path = new Path  Data = geometry ;
        Points = new PointCollection();           
    
    #endregion Constructors

    #region Properties
    /// <summary>
    /// Gets or sets a value that specifies the arc roundness.
    /// </summary>
    public Geometry Data
    
        get
        
            return _path.Data;
        
    

    /// <summary>
    /// Gets or sets a value that specifies if the polygon will be closed or not.
    /// </summary>
    public bool IsClosed
    
        get
        
            return _isClosed;
        
        set
        
            _isClosed = value;

        
    

    /// <summary>
    /// Gets or sets a collection that contains the points of the polygon.
    /// </summary>
    public PointCollection Points
    
        get  return _points; 
        set
        
            _points = value;

        
       

    protected override Geometry DefiningGeometry
    
        get
        
            return _path.Data;
        
    

    #endregion Properties

    #region Methods
    private static Point CreateRectangle(Point p1, Point p2, double distance, bool firstPoint)
    
        double segmentLength = Math.Sqrt(Math.Pow((p2.X - p1.X), 2) + Math.Pow((p2.Y - p1.Y), 2));
        //The distance cannot be greater than half of the length of the segment
        if (distance > (segmentLength / 2))
            distance = segmentLength / 2;
        double rap = firstPoint ? distance / segmentLength : (segmentLength - distance) / segmentLength;
        return new Point(p1.X + (rap * (p2.X - p1.X)), p1.Y + (rap * (p2.Y - p1.Y)));
    

    private static Point CreateCrosshair(Point p1, Point p2, double distancePercent, bool firstPoint)
    
        double rap = firstPoint ? distancePercent / 100 : (100 - distancePercent) / 100;
        return new Point(p1.X + (rap * (p2.X - p1.X)), p1.Y + (rap * (p2.Y - p1.Y)));
    
    #endregion Methods

    #region Other      

    #endregion Other

我是 C# 新手，我不知道为什么会发生错误。有人知道我应该如何纠正错误吗？

【问题讨论】：

什么是_activeType？

_activeType 是 Type 类的对象吗？

私有类型_activeType;

【参考方案1】：

我想你是说

_activeType = typeof(Reticle);

不是双重的==

【参考方案2】：

_activeType = typeof(Reticle);

== 是比较运算符（用于比较）