我正在编写一个需要在其主窗口区域之外绘制的应用程序。我已经必须编写代码才能实际进行绘图:
[DllImport("User32.dll")]
public static extern IntPtr GetDC(IntPtr hwnd);
[DllImport("User32.dll")]
public static extern void ReleaseDC(IntPtr hwnd, IntPtr dc);
IntPtr desktopPtr = GetDC(IntPtr.Zero);
Graphics g = Graphics.FromHdc(desktopPtr);
g.DrawLine(Pens.White, 0, 0, Screen.FromControl(this).WorkingArea.Width, Screen.FromControl(this).WorkingArea.Height);
g.Dispose();
ReleaseDC(IntPtr.Zero, desktopPtr);
但是,on paint 事件不适合放置代码,因为它不会在重绘窗体之外的内容时调用。所以我的问题是,这段代码可以放在哪里,以便在重绘屏幕的一部分时调用它?
最佳答案
如果您想要在屏幕上绘制内容,您应该始终创建一个窗口来保存该内容。在桌面(不属于您的窗口)上绘画不是个好主意。
解决方案是创建一个具有扩展样式 WS_EX_NOACTIVATE
的窗口,并在其上绘制以响应 WM_PAINT
消息。对于 WinForms 应用程序,运行时会在您获得 WM_PAINT
时调用 Form.OnPaint
,以便您可以处理该事件并在那里进行绘制。演示:
[DllImport("User32.dll")]
private static extern IntPtr GetWindowLong(IntPtr hWnd, int index);
[DllImport("User32.dll")]
private static extern int SetWindowLong(IntPtr hWnd, int index, IntPtr value);
[DllImport("User32.dll")]
private static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int X, int Y, int cx, int cy, uint uFlags);
static readonly IntPtr HWND_BOTTOM = new IntPtr(1);
private const int WS_EX_NOACTIVATE = 0x08000000;
private const int GWL_EXSTYLE = -20;
private const uint SWP_NOMOVE = 0x0002;
private const uint SWP_NOSIZE = 0x0001;
private const uint SWP_NOZORDER = 0x0004;
private const uint SWP_FRAMECHANGED = 0x0020;
private const uint StyleUpdateFlags = SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER | SWP_FRAMECHANGED;
public Form1()
{
InitializeComponent();
this.FormBorderStyle = FormBorderStyle.None;
this.Paint += Form1_Paint;
this.Shown += Form1_Shown;
}
private void Form1_Shown(object sender, EventArgs e)
{
IntPtr currentStyle = GetWindowLong(this.Handle, GWL_EXSTYLE);
int current = currentStyle.ToInt32();
current |= WS_EX_NOACTIVATE;
SetWindowLong(this.Handle, GWL_EXSTYLE, new IntPtr(current));
SetWindowPos(this.Handle, IntPtr.Zero, 0, 0, 0, 0, StyleUpdateFlags);
}
private void Form1_Paint(object sender, PaintEventArgs e)
{
e.Graphics.Clear(Color.Black);
}
如果您希望窗口 float 在顶部,请将表单的 TopMost
属性设置为 true。如果您希望您的窗口固定在 Z 顺序的底部(与 TopMost
完全相反),请将以下逻辑添加到您的表单中:
private struct WINDOWPOS
{
public IntPtr hwnd;
public IntPtr hwndInsertAfter;
public int x;
public int y;
public int cx;
public int cy;
public uint flags;
}
private const int WM_WINDOWPOSCHANGING = 0x0046;
protected override void WndProc(ref Message m)
{
if (m.Msg == WM_WINDOWPOSCHANGING)
{
if (m.LParam != IntPtr.Zero)
{
WINDOWPOS posInfo = Marshal.PtrToStructure<WINDOWPOS>(m.LParam);
posInfo.hwndInsertAfter = HWND_BOTTOM;
Marshal.StructureToPtr(posInfo, m.LParam, true);
m.Result = IntPtr.Zero;
return;
}
}
base.WndProc(ref m);
}
这会处理 WM_WINDOWPOSCHANGING
窗口消息,并通过告诉窗口管理器将窗口放在底部来防止窗口在 Z 顺序中向上移动。
关于c# - 在窗体区域外绘图时如何重绘,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/38034189/