修复背景粉碎 C# winform

Question

I work on MDIParent with background image after i move a child from in it the background image crush like this

how can i solve this issue in C# winforms??

Answer 1

The MDIClient Control is the object used, in Multiple-Document Interface, as the Container for all child Forms.

This Control has a BackGroundImage property. You can set an Image object using this property, instead of using the [MDIParent].BackGroundImage . This would actually solve the Image tearing problem.
But, you can't set a specific Layout property. See the Docs about the MDIClient BackgroundImageLayout :

This property is not relevant to this class.

You can set this property, but it's ignored: the default ImageLayout.Tile is used instead.
A different Layout can be set, assigning the Image object to the MDIParent BackGroundImage and specifying a BackGroundImageLayout . This will change the Layout, but it will also cause the tearing effect you are reporting.

A possible solution is to draw the Image object on the MDIClient surface, using it's Paint() event as usual.
This will solve the tearing effect. Not the flickering; this can be noticed when you resize the MDIParent Form (well, MDI applications are not resized that often, maybe maximized and normalized).
Some flickering can be seen when the background Image is not covered by a child Form.

A small adjustment to the Image specs is required: setting its DPI resolution = to the MDIParent reported device context DPI, otherwise the Image size will not match the default size (it's affected by the DPI resolution).

See this post for a description:
Image is not drawn at the correct spot .

An example:
(Here, I assume the background Image is loaded from the Project resources)

public partial class MDIParent : Form
{
    private MdiClient mdiBackground = null;
    private Bitmap BackGroundImage = null;

    public MDIParent()
    {
        InitializeComponent();
        //Specify an existing Resources' Image
        BackGroundImage = new Bitmap(Properties.Resources.[Some Res Image] as Bitmap);
        BackGroundImage.SetResolution(this.DeviceDpi, this.DeviceDpi);
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        mdiBackground = this.Controls.OfType<MdiClient>().First();

        mdiBackground.Paint += (s, evt) => {
            evt.Graphics.DrawImage(BackGroundImage,
                    (mdiBackground.Width - BackGroundImage.Width) / 2.0F,
                    (mdiBackground.Height - BackGroundImage.Height) / 2.0F);
        };
        //Show some child Forms on start-up
    }

    private void Form1_Resize(object sender, EventArgs e)
    {
        if (this.mdiBackground != null) mdiBackground.Invalidate();
    }

    private void MDIParent_FormClosed(object sender, FormClosedEventArgs e)
    {
        if (BackGroundImage != null) BackGroundImage.Dispose();
    }
}