Question

Hello it might be a silly question but i can’t figure out the problem here.. here is my code to fill a form with a single block:

    private void drawBackground()
{
    Graphics g = genPan.CreateGraphics();
    Image Block = Image.FromFile(@"C:\Users\Administrator\Desktop\movment V1\movment V1\images\BrownBlock.png");
    float recWidth = Block.Width; 
    // rectangle width didnt change the name from previous code, it's picture width.

    float recHeight = Block.Height;
    // rectangle Heightdidnt change the name from previous code, it's picture Height.

    float WinWidth = genPan.Width; // genPan is a panel that docked to the form

    float WinHeight = genPan.Height;

    float curWidth = 0; //indicates where the next block will be placed int the X axis
    float curHeight = 0;//indicates where the next block will be placed int the Y axis

    while ((curHeight + recHeight) <= WinHeight)
    {
        if (curWidth >= WinWidth / 3 || curWidth <= WinWidth / 1.5 ||
            curHeight >= WinHeight / 3 || curHeight <= WinHeight / 1.5)
        {
            g.DrawImage(Block, curWidth, curHeight, recWidth , recHeight );
        }
        curWidth += recWidth;
        if ((WinWidth - curWidth) < recWidth)
        {
            curWidth = 0;
            curHeight += 50;
        }
    }
}

If I launch this func through a button it will work perfectly fine. But if I launch the func after the InitializeComponent(); method in the constructor OR in a FORM shown event, while the button is still on the form it will execute the func however the block backgroud wont be visible but the grey color will be. but if i remove the button the background will be visible. =\

I cant understand why is it happening, how to fix it and what am I doing wrong.. can anyone explain please..?

Answer 1

You can’t really do that using your current logic. The problem is that the control (genPan panel in your case) has its own Paint event that when called, overwriting any graphics you used on it.

Even when you draw in button click it works only until the form is repainted e.g. try focus other window and focus your form again: you will lose what you have drawn.

Proper way to do such things is to write your own class that inherit from some basic control (Panel in your case) then overriding its OnPaint event and draw whatever you want there.

So first, have such class:

public class BlockBackgroundPanel : Panel
{
    protected override void OnPaint(PaintEventArgs e)
    {
        Graphics g = e.Graphics;
        Image Block = Image.FromFile(@"C:\Users\Administrator\Desktop\movment V1\movment V1\images\BrownBlock.png");
        float recWidth = Block.Width; 
        //rest of your code, replace "genPan" with "this" as you are inside the Panel
    }
}

Then in your .Designer.cs file (you can open it in the Studio) change the code so that genPan will be of your new class instance:

private BlockBackgroundPanel genPan;
//...
this.genPan = new BlockBackgroundPanel ();