.NET Framework - WPF textblock autosize : a kind of magic ???

Asked By Christian Hubert-Hugoud / weabow - Xtrem7 - Groobax

17-Mar-10 05:48 AM

I use a textblock in my personnal msgbox to display texts. Because of their
changing size, I want my textblock to become autosize. So when I set its
text property, I work a little bit :

public void printText( string TextToShow)
{
tMsg.Text = TextToShow;

// set the convenient height
Double lineHeight = tMsg.LineHeight;
System.Windows.Size desiredSize = new System.Windows.Size(
tMsg.Width, 1000);
tMsg.Height = desiredSize.Height * lineHeight;
}

What I do not understand, even if it works fine :

How the desiredSize is set to the right value, when I never tell in code
that it is linked to tMsg (textblock) ?

Christian

17-Mar-10 06:39 AM

Hi,

And what if you comment the tMsg.Height= line ? In whihc container is your
textblock.

You'll find at http://msdn.microsoft.com/en-us/library/ms745058.aspx, a
description of how WPF handles the layout (especially see the "Measuring and
Arranging Children" section). If I remember you have a first pass to measure
each element recursively based on their content and then you have a second
pass that does the actual layout...

I have only a theorical knwledge of WPF but AFAIK you do not have to code for
this (for now I believe the heght you gave is just too much and WPF
calculates another actual height).

--
Patrice


écrit dans le message de groupe de discussion :

17-Mar-10 07:26 AM

Presumably inside whatever container tMsg is you have your textblock.
Textblocks with no height or width set will take text and expand until they
fill their container.

Like a balloon in a box.
If you blow the balloon up, it will expand to fill the box.

So when you make it is container bigger, the textblock can expand to fill it,
if it is content needs to.

18-Mar-10 07:00 AM

Thanks to Andy & Patrice.

In fact, the desiredSize is computed each time a controle (?) is resized.

This function runs fine :

public void printText( TextBlock Target, string TextToShow)
{
Target.Text = TextToShow;

// set the convenient height
Double lineHeight = tMsg.LineHeight;
System.Windows.Size desiredSize = new
System.Windows.Size(Target.Width, 1000);
Target.Height = desiredSize.Height * lineHeight;
}

with theses calls  (2 tetxblocks):

printText(tMsg, TextToShow);
printText(tMsg2, "TextToShow\nCoucou : ceci est la seconde ligne
? ?tre imprim?e ici !");