Re: What Is A HitTest? - WPF Discussion Boards

Pete O'Hanlon7-Apr-11 6:27

7-Apr-11 6:27

Basically, this property determines whether or not a hit test can take place against a visual element. This has the effect of selectively altering the visual tree for the purposes of hit testing. Here's an example - suppose you have a map, and you want to get the coordinates of a point on the map - but you don't want any pushpins on it to be included in the tests, then setting this to false for the pushpins means the hit test would take place against the map, and not any pushpins.

I hope that explains it.

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

Kevin Marois7-Apr-11 6:32

7-Apr-11 6:32

Sort of.

I still don't understand what a HitTest is.

Everything makes sense in someone's mind

Pete O'Hanlon7-Apr-11 6:38

7-Apr-11 6:38

Ah. Imagine clicking on a point on the screen - the point you click at is the hit. It's a way of determining whether or not a control is affected by a click (perhaps you're writing a drag manager; and no this isn't your burly boss coming in wearing a dress)

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

Kevin Marois7-Apr-11 6:40

7-Apr-11 6:40

Ok, I got it. So IsHitTestVisible="False" means the object does not responde to a hit test?

Everything makes sense in someone's mind

Pete O'Hanlon7-Apr-11 6:51

7-Apr-11 6:51

Yes. A reason to do this is because you might have layered your control over the top of another one, and set it so that it's invisible - it will intercept mouse clicks destined for the lower control unless you set the hit test to false.

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

Kevin Marois7-Apr-11 6:52

7-Apr-11 6:52

ahh, ok. I get it.

Thanks

Everything makes sense in someone's mind

Pete O'Hanlon7-Apr-11 8:29

7-Apr-11 8:29

One more thing Kevin, and I apologise for not mentioning it. Setting IsHitTestVisible="false" on a container affects the children of the container as well. This is something to be very careful of because you can find that your hit testing doesn't behave quite the way you'd think it does by things higher up the tree. Here's a test for you to try:

XML

<Window
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  x:Class="HitTester.MainWindow"
  x:Name="Window"
  Title="Hit testable window"
  Width="788" Height="621">

  <Canvas IsHitTestVisible="False">
    <Button Content="Button" Width="75" IsHitTestVisible="True" />
  </Canvas>
</Window>

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

Kevin Marois7-Apr-11 8:45

7-Apr-11 8:45

Ok, will do. Thanks

Everything makes sense in someone's mind

Mycroft Holmes7-Apr-11 14:40

Mycroft Holmes

7-Apr-11 14:40

I'm so glad POH gave you a sensible answer b/c the first thing that I thought of was if someone smacks you in the face and you react then you have been hittested. A number of other facetious replies also occurred to me but you get the point. Laugh | :laugh:

Never underestimate the power of human stupidity
RAH

Pete O'Hanlon7-Apr-11 21:51

7-Apr-11 21:51

Actually, my first thought was to post that it was an online exam for assassins.

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

Message: The name already exists in the tree:

Mycroft Holmes7-Apr-11 22:14

Mycroft Holmes

7-Apr-11 22:14

You've been spending too much time in the Lounge listening to JSOP (and others) Wink | ;)

Never underestimate the power of human stupidity
RAH

Vimalsoft(Pty) Ltd6-Apr-11 23:42

6-Apr-11 23:42

This is the most Strangest error i have ever received from Silverlight. I have each control with its own name and i just added a Link button and a Menu item , i did a copy and paste of other items and renamed them from the xaml and i added a page that will be used by that menu item and i compiled the app and when i run it i get the following Error

Line: 54
Error: Unhandled Error in Silverlight Application 
Code: 2028    
Category: ParserError       
Message: The name already exists in the tree: EchashDev.     
File:      
Line: 0     
Position: 0

i tried googling and a lot of people are have different scenario which might be different from mine. I am not sure why Silverlight does not point to a problem element.

Thanks

Vuyiswa Maseko,

Spoted in Daniweb-- Sorry to rant. I hate websites. They are just wierd. They don't behave like normal code.

C#/VB.NET/ASP.NET/SQL7/2000/2005/2008
http://www.vuyiswamaseko.com
vuyiswa@its.co.za
http://www.itsabacus.co.za/itsabacus/

Re: Message: The name already exists in the tree: [modified]

Abhinav S7-Apr-11 18:14

Abhinav S

7-Apr-11 18:14

I believe you've added two components with the same name (or key).
A simple search within the code may give you an idea.

Also trying cleaning your solution once.

The funniest thing about this particular signature is that by the time you realise it doesn't say anything it's too late to stop reading it.

Vimalsoft(Pty) Ltd7-Apr-11 18:48

7-Apr-11 18:48

thanks for your reply. It was a bit complicated than that, the problem is now resolved , here was a problem.

i Had two Projects, opened. i was doing my demo on one project , so they liked it and i copied some controls and paste from one project to another and it created a reference and now it means the control exists in two projects that are linked so it caused a Conflict.

When i was typing some namespaces , i realised that there were namespaces that i did not create and i looked at the name of the demo project and i realised that i could access its object from another class. So i went to the References in the solution explorer and there was a dead reference marked with an exclation mark and i knew it was it.

its a lesson , don't copy controls between projects unless you copy code.

I see there is a duplicate post , please delete it. i think it was created when i lost connection trying to post the question.

thanks

modified on Friday, April 8, 2011 4:12 PM

Pete O'Hanlon7-Apr-11 22:15

7-Apr-11 22:15

We can't delete it, but you can. We'll leave it with no answers so you can remove it.

Good job on finding the solution.

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

Vimalsoft(Pty) Ltd8-Apr-11 1:13

8-Apr-11 1:13

Thank you , i just deleted the post.

kind Regards

Vuyiswa Maseko

Abhinav S8-Apr-11 8:20

Abhinav S

8-Apr-11 8:20

Thanks for posting the solution.

The funniest thing about this particular signature is that by the time you realise it doesn't say anything it's too late to stop reading it.

Vimalsoft(Pty) Ltd8-Apr-11 10:12

8-Apr-11 10:12

You are Welcome Smile | :)

Logical vs Visual Tree

devvvy6-Apr-11 21:45

devvvy

6-Apr-11 21:45

After programming WPF for sometime and reading so many articles[^] ... I'm still a little bit confused distinction between Logical and Visual Tree.

To simply put, my understanding is that Logical Tree is just a simplified version of Visual Tree! They are no different is just a way to confuse developers, they really should have one tree type - i.e. Visual Tree

And one additional property to let the guy decide if they need detail or not:

VisualTree.Mode = PresentationMode.Simple (i.e. LogicalTree) or PresentationMode.Complex (i.e. VisualTree)

Am I missing something here?

dev

Pete O'Hanlon6-Apr-11 22:06

6-Apr-11 22:06

You're missing quite a lot. While it may have been possible to combine the two types of trees, the resulting kludge would have been quite horrible.

Something that most people don't realise is that, while there is only one visual tree in a WPF application, there can be many logical trees. This is down to the purpose that they serve, and also covers the fact that the visual tree can only work with elements derived from Visual or Visual3D (hence it's name) while the logical tree can contain any type of object (and is one of the reasons that LogicalTreeHelper is not the most optimal way of walking the logical tree because it only walks DependencyObject elements. Without logical trees, it would be impossible for WPF/Silverlight to be able to use templates, for instance.

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

devvvy6-Apr-11 22:25

devvvy

6-Apr-11 22:25

hi Peter, can you point me to a decent url? I been coding WPF for almost two years, didn't buy any book but did read quite numerous articles. Still in the dark.

thanks

dev

Pete O'Hanlon6-Apr-11 22:28

6-Apr-11 22:28

Josh Smith wrote an excellent article on the two. You can find it here[^].

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

Pete O'Hanlon6-Apr-11 23:37

6-Apr-11 23:37

I should have added that this is an excellent question - because the differences between the two are not very well explained in the documentation. Let me correct that voting oversight.

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads