Setting Margin Properties in code

Question

MyControl Margin Left   10    Error      Cannot modify the return value of  System Windows FrameworkElement Margin  because it is not a variable

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The Margin property returns a Thickness structure  of which Left is a property  What the statement does is copying the structure value from the Margin property and setting the Left property value on the copy  You get an error because the value that you set will not be stored back into the Margin property    Earlier versions of C  would just let you do it without complaining  causing a lot of questions in newsgroups and forums on why a statement like that had no effect at all      To set the property you would need to get the Thickness structure from the Margin property  set the value and store it back   Thickness m   MyControl Margin  m Left   10  MyControl Margin   m    If you are going to set all the margins  just create a Thickness structure and set them all at once   MyControl Margin   new Thickness 10  10  10  10

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Margin   new Thickness 0  0  0  0

User · Answer

To use Thickness you need to create change your project  NET framework platform version to 4 5  becaus this method available only in version 4 5   Also you can just download PresentationFramework dll and give referense to this dll  without create change your  NET framework version to 4 5     But if you want to do this simple  You can use this code   MyControl Margin   new Padding int left  int top  int right  int bottom     also   MyControl Margin   new Padding int all     This is simple and no needs any changes to your project

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It s a bit unclear what are you asking  but to make things comfortable  you can inherit your own Control and add a property with the code that Marc suggests   class MyImage   Image       private Thickness thickness      public double MarginLeft           get   return Margin Left            set   thickness   Margin  thickness Left   value  Margin   thickness              Then in the client code you can write just  MyImage img   new MyImage    img MarginLeft   10  MessageBox Show img Margin Left ToString        or img MarginLeft

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One would guess that  and my WPF is a little rusty right now  that Margin takes an object and cannot be directly changed   e g   MyControl Margin   new Margin 10 0 0 0

User · Answer

Margin is returning a struct  which means that you are editing a copy  You will need something like   var margin   MyControl Margin  margin Left   10  MyControl Margin   margin

User · Answer

The problem is that Margin is a property  and its type  Thickness  is a value type  That means when you access the property you re getting a copy of the value back   Even though you can change the value of the Thickness Left property for a particular value  grr    mutable value types shouldn t exist   it wouldn t change the margin   Instead  you ll need to set the Margin property to a new value  For instance  coincidentally the same code as Marc wrote    Thickness margin   MyControl Margin  margin Left   10  MyControl Margin   margin    As a note for library design  I would have vastly preferred it if Thickness were immutable  but with methods that returned a new value which was a copy of the original  but with one part replaced  Then you could write   MyControl Margin   MyControl Margin WithLeft 10     No worrying about odd behaviour of mutable value types  nice and readable  all one expression

User · Answer

One could simply use this  MyControl Margin   new System Windows Thickness 10  0  5  0

User · Answer

Depends on the situation  you can also try using padding property here     MyControl Margin new Padding 0 0 0 0

[c#] Setting Margin Properties in code

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