C# 如何在C中将EM_CHARFROMPOS与RichTextBox一起使用#

我试图使用以下代码在RichTextBox中按位置检索字符索引。我知道我可以使用RichTextBox类提供的GetCharIndexFromPosition方法，但我想知道以下代码有什么问题：

SendMessage导入是这样的：

[DllImport("User32.dll", EntryPoint = "SendMessage", CharSet= CharSet.Auto)]
public static extern IntPtr SendMessage(IntPtr hWnd, int msg, int wParam, ref POINTL lParam);

然后这个电话：

int returnVal = (int)WinUser.SendMessage(this._textBox.Handle, (int)WinUser.Message.EM_CHARFROMPOS, 0, ref p);

其中p是包含屏幕坐标的POINTL结构实例，其中RichTextBox的左上角为原点

POINTL结构定义为

[StructLayout(LayoutKind.Sequential)]
public struct POINTL
{
    public long x;
    public long y;
}

    public override int GetCharIndexFromPosition(Point pt) { 
        NativeMethods.POINT wpt = new NativeMethods.POINT(pt.X, pt.Y);
        int index = (int)UnsafeNativeMethods.SendMessage(new HandleRef(this, Handle), NativeMethods.EM_CHARFROMPOS, 0, wpt); 

        string t = this.Text;
        // EM_CHARFROMPOS will return an invalid number if the last character in the RichEdit
        // is a newline. 
        //
        if (index >= t.Length) { 
            index = Math.Max(t.Length - 1, 0); 
        }
        return index; 
    }

    [StructLayout(LayoutKind.Sequential)] 
    public class POINT {
        public int x; 
        public int y; 

        public POINT() { 
        }

        public POINT(int x, int y) {
            this.x = x; 
            this.y = y;
        } 

#if DEBUG
        public override string ToString() { 
            return "{x=" + x + ", y=" + y + "}";
        }
#endif
    } 

点Lp已初始化为：

WinUser.POINTL p;
p.x = 0;
p.y = 0;

现在的问题是：

如果p按照上面给出的方式初始化，则返回值为0

如果p是{x=10，y=10}或{x=1，y=1}之类的值，则returnVal为1

---

在这两种情况下，函数GetCharIndexFromPosition都提供了正确的索引。

将

long

更改为

int

（Win32

LONG

s是与.Net

int

s相对应的32位整数）

.Net的

GetCharIndexFromPosition

方法定义为

[StructLayout(LayoutKind.Sequential)]
public struct POINTL
{
    public long x;
    public long y;
}

    public override int GetCharIndexFromPosition(Point pt) { 
        NativeMethods.POINT wpt = new NativeMethods.POINT(pt.X, pt.Y);
        int index = (int)UnsafeNativeMethods.SendMessage(new HandleRef(this, Handle), NativeMethods.EM_CHARFROMPOS, 0, wpt); 

        string t = this.Text;
        // EM_CHARFROMPOS will return an invalid number if the last character in the RichEdit
        // is a newline. 
        //
        if (index >= t.Length) { 
            index = Math.Max(t.Length - 1, 0); 
        }
        return index; 
    }

    [StructLayout(LayoutKind.Sequential)] 
    public class POINT {
        public int x; 
        public int y; 

        public POINT() { 
        }

        public POINT(int x, int y) {
            this.x = x; 
            this.y = y;
        } 

#if DEBUG
        public override string ToString() { 
            return "{x=" + x + ", y=" + y + "}";
        }
#endif
    } 

NativeMethods.POINT

类型定义为

[StructLayout(LayoutKind.Sequential)]
public struct POINTL
{
    public long x;
    public long y;
}

    public override int GetCharIndexFromPosition(Point pt) { 
        NativeMethods.POINT wpt = new NativeMethods.POINT(pt.X, pt.Y);
        int index = (int)UnsafeNativeMethods.SendMessage(new HandleRef(this, Handle), NativeMethods.EM_CHARFROMPOS, 0, wpt); 

        string t = this.Text;
        // EM_CHARFROMPOS will return an invalid number if the last character in the RichEdit
        // is a newline. 
        //
        if (index >= t.Length) { 
            index = Math.Max(t.Length - 1, 0); 
        }
        return index; 
    }

    [StructLayout(LayoutKind.Sequential)] 
    public class POINT {
        public int x; 
        public int y; 

        public POINT() { 
        }

        public POINT(int x, int y) {
            this.x = x; 
            this.y = y;
        } 

#if DEBUG
        public override string ToString() { 
            return "{x=" + x + ", y=" + y + "}";
        }
#endif
    } 

---

这起作用了。如何看待.NET中函数的实际实现。就像你在这里给的那个？