Develop Reference

How to place a label or a button exactly in the middle of the Form?

I can't find tools or properties to place a label or a button exactly in the middle of the Form. For example, on the X axis. VS 2015.

Design time :
In my VisualStudio2010 I have these 2 buttons to center horizontally and vertically:
Its located in the toolbar "Layout". If it isn't, you can add them by clicking the small button to the right. It is also in the Format menu.
To keep centered at Runtime: Turn off all anchoring.
Note:This will keep the control at its relative position as long as it doesn't change it Size. If it does, like autosize Labels are prone to, you will have to code the Resize event. Examples are here

For controls that may change in size, you need to catch the Resize event.
In my case I have a Panel, representing a page, inside another Panel which is the workspace. The workspace is set to autoscroll. In this scenario, it's important that the control is only centered when smaller than the container.
Whenever the form changes size or when I change the content, I call this function:
private void resetPagePos()
{
int wWS = pnlWorkspace.Width;
int hWS = pnlWorkspace.Height;
int wPage = pnlPage.Width;
int hPage = pnlPage.Height;
pnlPage.Location = new Point(Math.Max(0, (wWS - wPage) / 2), pnlPage.Top = Math.Max(0, (hWS - hPage) / 2));
}
The use of Math.Max(0, ...) makes sure that if the item doesn't fit, and the scrollbars are activates, then our page scrolls correctly. If the Left or Top are set to a negative number, you would get unwanted side-effects.

WPF Canvas Only Extends to the Right?

I'm making a WPF application using C# and I am in the stage of developing more UI for it. I have all my components such as TextBlocks and other Canvases inside of a main Canvas, but if I drag the left side of it to make more room, it expands on the right side, meaning I have to move everything over. The same thing happens when I try and extend the top; The bottom gets bigger. I have the RenderTransformOrigin of the Canvas set to 0,0 so I'm not quite sure what is going on. Any help is appreciated.
Thanks!

By default, a Canvas doesn't have a Width or Height, its actual size depends if you set those properties explicitly, or if you set HorizontalAlignment or VerticalAlignment to Stretch.
In either case, elements inside of a Canvas are aligned relative to its top-left corner, except if you explicitly set their Canvas.Top, Canvas.Left, Canvas.Right and/or Canvas.Bottom properties.
You could also position elements containing a Geometry (like derivatives of Shape, Path being a common example) by their absolute Geometry coordinates. Actually this already is the way they are rendered.
Regarding your comment in the question, usually you don't change where things align relative to the Canvas, since it is much easier (I think even recommended) to reposition the canvas itself, so that everything it contains would be repositioned too.
Common ways to do that would be adding elements to a Canvas, and then position that Canvas inside another "parent" Canvas, similar to "grouping" in vector design programs like CorelDraw/Inkscape/Illustrator.
Another way would be to use RenderTransform property of Canvas containing the elements you want to reposition.
After you get used to see Canvas as a "coordinate system", you can and should think of Canvas-inside-Canvas-inside-Canvas-... as a way of hierarchically grouping things that share the same cartesian space, as opposed to Panels and ContentControls, which are nested inside one another and cannot typically share space.

Like I said in my comment, all the controls inside the canvas are positioned relative to the canvas' top left point. If you want them to retain their "position" when the canvas is resized to the left or top, you will need to offset them yourself. You could do this with a utility method that you call whenever you want to resize the canvas:
public static void StretchWidthLeft(Canvas canvas, double newWidth)
{
double diff = newWidth - canvas.Width;
canvas.Width = newWidth;
foreach (UIElement child in canvas.Children)
{
Canvas.SetLeft(child, Canvas.GetLeft(child) + diff);
}
}
public static void StretchHeightTop(Canvas canvas, double newHeight)
{
double diff = newHeight - canvas.Height;
canvas.Height = newHeight;
foreach (UIElement child in canvas.Children)
{
Canvas.SetTop(child, Canvas.GetTop(child) + diff);
}
}
Note that these methods do not reposition the canvases themselves. How you would do that depends on how the canvas' parent is maintaining their position.

How to determine if control is outside of Form?

I am trying to determine if a dynamically added control is outside of the form.
At first, I thought it might be possible to calculate it by getting the height of the form, and location of the dynamically added control.
But I noticed that the Control.Location and Form.Height have "nothing" in common.
I don't think I really understand what the correlation is between Height and Location.
For example:
I thought that if your form has a height of 500, and I put the control at the bottom of the form, it should give the Location: X, 500 (X is width, not relevant here). But this is not correct, it shows me for example: X, 465. Am I missing something?
So I need to be able to recognize if the control is outside of the form, even if it's just one pixel.
I've found several similar questions here on SO, yet this does not really give me the answer that I need, unfortunately.
So, is there any way to do this? Is it possible to calculate it?

The Height of the form also includes the height of the title bar and borders.
You can use the ClientSize of the form:
From the documentation on MSDN:
The size of the client area of the form is the size of the form excluding the borders and the title bar. The client area of a form is the area within a form where controls can be placed. You can use this property to get the proper dimensions when performing graphics operations or when sizing and positioning controls on the form. To get the size of the entire form, use the Size property or use the individual properties Height and Width.
The position of the control is relative to its container, so (0,0) is the left upper corner inside the form.

I know this is an older thread, but you can try using this method:
public static bool IsOutofBounds(Form form, Control control)
{
int controlEnd_X = control.Location.X + control.ClientSize.Width;
int controlEnd_Y = control.Location.Y + control.ClientSize.Height;
if (form.ClientSize.Width < controlEnd_X || form.ClientSize.Height < controlEnd_Y)
{
return true;
}
else
{
return false;
}
}
It works for checking whether a control is out of bounds of its parent form.

You could use this code to check if controls is inside form:
var Inside = frm.ClientRectange.Intersect(ctrl.Bounds) == ctrl.Bounds;

the top left corner of a form is (0,0) lower right corner is (formHeight, fromWidth).
to check this place two text boxes on a form and write this code in the mouse move event to see how x and y change.
private void Form1_MouseMove(object sender, MouseEventArgs e)
{
textBox1.Text = e.X.ToString();
textBox2.Text = e.Y.ToString();
}
Note that there is an difference between the number returned from the edge of the form and the size chosen by you. In my 500*500 form it is actually 460*483. the difference is always the same for any border style and any resolution.
To place a control on your form use the location structure in the form or use the top and left properties for the control; top = x, left = y.
Remember your offset from the actual height and width you measured and the dimension of the control.
To add a button with the following dimensions 80*30 in the bottom right corner I would right something like this:
button1.Location = new System.Drawing.Point(402, 430);
bottom left corner:
button1.Location = new System.Drawing.Point(0, 430);

Canvas has Width of 0 after adding children. How to cause canvas to recalculate width?

I'm creating a custom canvas which has dynamically added shapes (lines) which are added as children. Unfortunately, after adding the children, the canvas has a width of 0, which is not expected.
Ideally, the canvas should update its width by using its children's dimensions.
How can I modify my canvas to account for the dimensions of its children, and then update its width?
As I said, I changed the shapes on the canvas dynamically. I do this every time one of its dependency properties is changed using a callback function.
Generally, this is what that callback function looks like:
This is not my algorithm, but it should demonstrate the point.
public void UpdateLines()
{
for(int i = 0; i < NUM_BARS; i++)
{
Line bar = new Line();
bar.Stroke = Brushes.Black;
bar.StrokeThickness = 4;
bar.X1 = 0;
bar.X2 = ActualWidth;
bar.Y1 = i * (bar.StrokeThickness + 2);
bar.Y1 = bar.Y2;
this.Children.Add(bar);
}
//[Inserted here]
}
The next thing I noticed is that I could add a line with a large length, and that line would appear, but the canvas width would still remain 0.
At the "Inserted Here" mark, I put this line of code to test:
Children.Add(new Line() { Stroke=Brushes.Black,
StrokeThickness = 4, X1 = 0, X2 = 200, Y1 = 10, Y2 = 10 });
So, why the canvas width is not updating properly? I need to use it for calculating the size of my lines.
Your help is greatly appreciated. Thanks.

Please refer to the Panels Overview page on MSDN for further help with WPF Panels, but in short, the Canvas Panel does not resize itself when child items are added (or at any time). From the linked page:
Canvas is not affected by the size of its children. As a result, it is possible for a child element to overdraw other elements outside the bounding rectangle of the parent Canvas.
Therefore, you will either need to manually update the size of the Canvas, or use a different type of layout Panel that does resize itself when child items are added, although the Canvas is the only Panel that enables users to place child controls at absolute positions within it.
Again, from the linked page:
Canvas provides the most flexible layout support of any Panel. Height and Width properties are used to define the area of the canvas, and elements inside are assigned absolute coordinates relative to the area of the parent Canvas. Four attached properties, Canvas.Left, Canvas.Top, Canvas.Right and Canvas.Bottom, allow fine control of object placement within a Canvas, allowing the developer to position and arrange elements precisely on the screen.

Windows Forms' PictureBox with zooming and panning

My application needs control displaying bitmaps (jpg) but also zooming and panning them (so if you press mouse button you can 'move' zoomed picture inside frame)
What I did was placing panel at the Form, then pictureBox inside panel (anchored Top,Left).
So if I need zoom it I'm just executing below code from Zoom buttons events:
private void ZommInOut(bool zoom) {
int zoomRatio = 10; // percent
int widthZoom = pBox.Width * zoomRatio /100;
int heightZoom = pBox.Height * zoomRatio /100;
if (zoom) {
widthZoom *= -1;
heightZoom *= -1;
}
pBox.Width += widthZoom;
pBox.Height += heightZoom;
}
Works petty well. Image is zoomed, panel displaying scrollbars - so I have working simple panning functionality.
What is missing to me is possibility to use mouse for panning - I'd like to drag picture in any direction to see other part of picture (as eg Acrobat Reader does).
I've looked for the way to use MouseMove event and change scrollbars programically but I couldn't manage that.
Any suggestion(s)?

You need to set the AutoScrollPosition property in the MouseMove event.
You'll need to track the location of the MouseDown event and update AutoScrollPosition using an offset.

I would suggest creating a control and drawing part of the image using Graphics.DrawImage - in this way you can control how the image is scaled (trilinear etc) and it will also use less memory. You can override OnMouseMove to get the mosue movements