Question

我有一个自定义类CurvePoint，我使用DrawCurve

定义了一组要在屏幕上绘制的数据项

我编写了一个转换例程来将CurvePoint转换为Point，但是我收到了错误 源阵列中至少有一个元素无法转换为目标数组类型。当我尝试在Arraylist中使用.ToArray方法时

我可以使用代码将对象强制转换：

Point f = new CurvePoint(.5F, .5F, new Rectangle(0, 0, 10, 10));

但如果在使用

时失败

Point[] Plots=(Point[])_Data.ToArray(typeof(Point));

（其中_Data是一个填充了5个CurvePoint对象的ArrayList）

以下是完整代码：



public partial class Chart : UserControl
{
    ArrayList _Data;
    public Chart()
    {
        InitializeComponent();
        _Data = new ArrayList();
        _Data.Add(new CurvePoint(0f, 0f,this.ClientRectangle));
        _Data.Add(new CurvePoint(1f, 1f, this.ClientRectangle));
        _Data.Add(new CurvePoint(.25f, .75f, this.ClientRectangle));
        _Data.Add(new CurvePoint(.75f, .25f, this.ClientRectangle));
        _Data.Add(new CurvePoint(.5f, .6f, this.ClientRectangle));
    }
    private void Chart_Paint(object sender, PaintEventArgs e)
    {
        _Data.Sort();
        e.Graphics.FillEllipse(new SolidBrush(Color.Red),this.ClientRectangle);
        Point[] Plots=(Point[])_Data.ToArray(typeof(Point));
        e.Graphics.DrawCurve(new Pen(new SolidBrush(Color.Black)), Plots);
    }
}
public class CurvePoint : IComparable
{
    public float PlotX;
    public float PlotY;
    public Rectangle BoundingBox;
   public CurvePoint(float x, float y,Rectangle rect)
    {
        PlotX = x; PlotY = y;
        BoundingBox = rect;
    }

    public int CompareTo(object obj)
    {
        if (obj is CurvePoint)
        {
            CurvePoint cp = (CurvePoint)obj;
            return PlotX.CompareTo(cp.PlotX);
        }
        else
        { throw new ArgumentException("Object is not a CurvePoint."); }
    }
    public static implicit operator Point(CurvePoint x)
    {
        return new Point((int)(x.PlotX * x.BoundingBox.Width), (int)(x.PlotY * x.BoundingBox.Height));
    }
   public static implicit operator string(CurvePoint  x)
    {
        return x.ToString();
    }
   public override string ToString()
    {
        return "X=" + PlotX.ToString("0.0%") + " Y" + PlotY.ToString("0.0%");
    }

}

public partial class Chart : UserControl { ArrayList _Data; public Chart() { InitializeComponent(); _Data = new ArrayList(); _Data.Add(new CurvePoint(0f, 0f,this.ClientRectangle)); _Data.Add(new CurvePoint(1f, 1f, this.ClientRectangle)); _Data.Add(new CurvePoint(.25f, .75f, this.ClientRectangle)); _Data.Add(new CurvePoint(.75f, .25f, this.ClientRectangle)); _Data.Add(new CurvePoint(.5f, .6f, this.ClientRectangle)); } private void Chart_Paint(object sender, PaintEventArgs e) { _Data.Sort(); e.Graphics.FillEllipse(new SolidBrush(Color.Red),this.ClientRectangle); Point[] Plots=(Point[])_Data.ToArray(typeof(Point)); e.Graphics.DrawCurve(new Pen(new SolidBrush(Color.Black)), Plots); } } public class CurvePoint : IComparable { public float PlotX; public float PlotY; public Rectangle BoundingBox; public CurvePoint(float x, float y,Rectangle rect) { PlotX = x; PlotY = y; BoundingBox = rect; } public int CompareTo(object obj) { if (obj is CurvePoint) { CurvePoint cp = (CurvePoint)obj; return PlotX.CompareTo(cp.PlotX); } else { throw new ArgumentException("Object is not a CurvePoint."); } } public static implicit operator Point(CurvePoint x) { return new Point((int)(x.PlotX * x.BoundingBox.Width), (int)(x.PlotY * x.BoundingBox.Height)); } public static implicit operator string(CurvePoint x) { return x.ToString(); } public override string ToString() { return "X=" + PlotX.ToString("0.0%") + " Y" + PlotY.ToString("0.0%"); } }

有人可以说如何修复代码吗？

Answer 1

首先，我将您的ArrayList更改为强类型通用列表List<CurvePoint>。然后，要获取Point数组，可以执行此代码。

Point[] Plots = _Data.Select(obj => (Point)obj).ToArray();

如果将其保留为ArrayList，您仍然可以使用以下代码执行此操作：

Point[] Plots = (from CurvePoint obj in _Data select (Point)obj).ToArray();
// or
Point[] Plots = _Data.Cast<CurvePoint>().Select(obj => (Point)obj).ToArray();

编辑：最后，如果您遇到了ArrayList 和，那么您没有LINQ，那么您可以采用“长”方式。

Point[] Plots = new Point[_Data.Count];
for (int i = 0; i < _Data.Count; i++)
{
    Plots[i] = (Point)(CurvePoint)_Data[i];
}

Answer 2

你不能这样做的原因是你的ArrayList通过对对象的引用包含点。因此，没有用户定义的对象转换（即使它是对CurvePoint的引用，它确实有定义的转换）到你的Point类型。

以下修复程序将起作用（.NET 3.5 +）：

        Point[] Plots = _Data
            .OfType<CurvePoint>()
            .Select(cp => (Point)cp)
            .ToArray();

ArrayList对象到Point对象的数组

2 个答案: