wpf - DependencyProperty Registration in ViewModel -

i finding lot of discussions viewmodels , properties compare 2 approches: implementation of inotifypropertychanged or implementation via dependency properties.

while doing inotifypropertychanged lot (and it's working) having difficulties implementing dp-approach.

when registering dp in viewmodel this

    public static readonly dependencyproperty somepropertyproperty =         dependencyproperty.register("someproperty", typeof(string), typeof(myusercontrol)); 

and trying use somewhere with:

<mynamespace:myusercontrol someproperty="{binding ...}"/> 

there compiler error:

the property 'someproperty' not exist in xml namespace 'clr-namespace:mynamespace'. 

what doing wrong??

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edit1

the viewmodel looks this:

public class myusercontrolvm : dependencyobject {      public string someproperty     {         { return (string)getvalue(somepropertyproperty); }         set { setvalue(somepropertyproperty, value); }     }      public static readonly dependencyproperty somepropertyproperty =         dependencyproperty.register("someproperty", typeof(string), typeof(myusercontrol));      } 

have implemented standard property accessors? complete dp signature looks this:

public static readonly dependencyproperty propertynameproperty =         dependencyproperty.register("propertyname", typeof (propertytype), typeof (myuserviewmodel), new propertymetadata(default(propertytype)));      public propertytype propertyname     {         { return (propertytype) getvalue(propertynameproperty); }         set { setvalue(propertynameproperty  value); }     } 

then code should work. 1 more info regarding dp's vs. inotifypropertychanged: me, main tradeoff speed vs. readability. it's pain littering viewmodels dependency property declarations, gain 30% speed in notification pipeline.

edit:

you register property on view's type, should viewmodel's type, i.e.

public static readonly dependencyproperty propertynameproperty =         dependencyproperty.register("propertyname",          typeof (propertytype),          typeof (myuserviewmodel),          new propertymetadata(default(propertytype))); 

instead of

public static readonly dependencyproperty propertynameproperty =         dependencyproperty.register("propertyname",          typeof (propertytype),         typeof (myusercontrol),          new propertymetadata(default(propertytype))); 

edit 2:

ok, you're mixing here: can have dependency properties both, on viewmodel , view. former, define dp in control's codebehind (i.e. myusercontrol.xaml.cs). latter define in viewmodel have shown above. problem code lies in usage:

you trying bind value of datacontext property called someproperty on view:

<mynamespace:myusercontrol someproperty="{binding somepropertybindingvalue}"/> 

as you've defined dependency property on view model, there no property someproperty on view, hence compiler error. make above usage work, need put dp in view's codebehind , define normal property somepropertybindingvalue on viewmodel.

to define dp on viewmodel , use in view, need bind property:

<mynamespace:myusercontrol width="{binding someproperty}"/> 

supposed you've wired viewmodel , view correctly, bind views width viewmodel's property someproperty. now, if someproperty set on viewmodel, ui update, though haven't implemented inpc.

edit 3:

from understand problem - desired behavior - need bind 1 dependency property on control 2 properties on separate viewmodels: 1 property on mainwindowvm should bound usercontrol , - usercontrol - viewmodel (usercontrol1vm). there bit of twist in design here , without knowing exact context, don't see why couldn't handle property synch on viewmodel level:

i let viewmodels more or less resemble nested structure of view:

say have view (pseudo-code):

<window>     <usercontrol1 /> </window> 

let data context of window mainwm, whereever comes from, not proper xaml(!):

<window datacontext="[mainvm]">     <usercontrol1 /> </window> 

question 1 is, why user control need it's own viewmodel? bind *mainvm*s property 'someproperty':

<window datacontext="[mainvm]">     <usercontrol text="{binding someproperty}" /> </window> 

ok, have agood reason why need usercontrolviewmodel has it's own property 'ucsomeproperty':

public class usercontrolvm {     public string ucsomeproperty { get; set; } // let inpc etc. implemented } 

add usercontrolvm property mainvm:

public class mainvm {     public usercontrolvm usercontrolvm { get; set; } // inpc etc. } 

now, can set binding:

<window datacontext="[mainvm]">     <usercontrol datacontext="{binding usercontrolvm}"                   text="{binding ucsomeproperty}" /> </window> 

last, again without knowing specific case , whether makes sense, let's want property on 'mainvm' in synch property on user control's viewmodel's property:

public class mainvm {     public string someproperty     {          { return usercontrolvm.ucsomeproperty; }          set { usercontrolvm.ucsomeproperty = value; }     }      public usercontrolvm usercontrolvm { get; set; } // inpc etc.      public mainvm()     {          usercontrolvm = new usercontrolvm();          usercontrolvm.notifypropertychanged += usercontrolvm_propertychanged;     }      private void usercontrolvm_propertychanged(object sender, blaargs e)     {          if (e.propertyname == "ucsomeproperty")               raisepropertychanged("someproperty");     }  } 

you use binding this, example:

 <window datacontext="[mainvm]">     <usercontrol datacontext="{binding usercontrolvm}"                   text="{binding ucsomeproperty}" />     <textblock text="{binding someproperty}" /> </window> 

someproperty on mainvm , ucsomeproperty on usercontrolvm same , available on both viewmodels. hope helps...