I'm making a simple graphic editor in Windows Forms (C#), and I'm using a PictureBox for my canvas. I want to implement the "undo" functionality. I'm drawing using System.Drawing.Graphics. Here is my situation:
我正在Windows Forms（C＃）中创建一个简单的图形编辑器，我正在使用PictureBox作为我的画布。我想实现“撤消”功能。我正在使用System.Drawing.Graphics绘图。这是我的情况：
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If I use
picturebox.CreateGraphics(), then I will see the drawing, but it won't actually be made on the image (if afterwards I calledpictureBox.Image.Save(...), the saved image would be blank).如果我使用picturebox.CreateGraphics（），那么我将看到绘图，但它实际上不会在图像上进行（如果之后我调用了pictureBox.Image.Save（...），保存的图像将为空白） 。
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If I use
Graphics.FromImage(picturebox.Image), then the drawing will be actually made on the image, but I won't see anything.如果我使用Graphics.FromImage（picturebox.Image），那么绘图将实际在图像上进行，但我什么都看不到。
How can I have both?
我怎么能同时拥有？
And how do I implement the undo functionality after that? I tried using Save() and Restore() on graphics, but it didn't work, maybe I misunderstood what these methods mean.
那之后如何实现撤消功能呢？我尝试在图形上使用Save（）和Restore（），但它不起作用，也许我误解了这些方法的含义。
1 个解决方案
#1
3
You should avoid using CreateGraphics since that is a temporary drawing that can get erased by minimizing the form or having another form overlap the graphic area, etc.
您应该避免使用CreateGraphics，因为这是一个临时绘图，可以通过最小化窗体或使另一个窗体重叠图形区域等来删除。
To update the PictureBox, just invalidate it after you have an update to the drawing:
要更新PictureBox，只需在更新绘图后使其无效：
pictureBox1.Invalidate();
The Undo-Redo is a different beast. That requires you to keep a list of things to draw and in order to undo something, you remove the item from the list and redraw the whole thing again from the active list.
Undo-Redo是一个不同的野兽。这需要您保留要绘制的内容列表，并且为了撤消某些内容，您从列表中删除该项目并从活动列表中重新绘制整个内容。
#1
3
You should avoid using CreateGraphics since that is a temporary drawing that can get erased by minimizing the form or having another form overlap the graphic area, etc.
您应该避免使用CreateGraphics，因为这是一个临时绘图，可以通过最小化窗体或使另一个窗体重叠图形区域等来删除。
To update the PictureBox, just invalidate it after you have an update to the drawing:
要更新PictureBox，只需在更新绘图后使其无效：
pictureBox1.Invalidate();
The Undo-Redo is a different beast. That requires you to keep a list of things to draw and in order to undo something, you remove the item from the list and redraw the whole thing again from the active list.
Undo-Redo是一个不同的野兽。这需要您保留要绘制的内容列表，并且为了撤消某些内容，您从列表中删除该项目并从活动列表中重新绘制整个内容。