Unable to position Rectangle in Canvas in Silverlight 4 -

i'm new sl. wrote simple app drawing rectangle , line. when try position rectangle has no effect , puts in lower-right corner:

canvas.setleft(r, 100); canvas.settop(r, 100); 

when try use setvalue, app hangs (ie. stuck on loading animation in browser):

r.setvalue(canvas.leftproperty, 10); r.setvalue(canvas.topproperty, 10); 

has experienced this, and/or know how past it?

[edit] here's more complete source:

    public mainpage()     {         initializecomponent();          rectangle r = new rectangle() {             stroke = new solidcolorbrush(colors.black),             width = 100,             height = 20,             fill = new solidcolorbrush { color = color.fromargb(80, 143, 12, 28) }         };         //r.setvalue(canvas.leftproperty, 10);         //r.setvalue(canvas.topproperty, 10);         canvas.setleft(r, 100);         canvas.settop(r, 100);         this.layoutroot.children.add(r);          var line = new line() {             stroke = new solidcolorbrush(colors.black),             x1 = 10, y1 = 10, x2 = 100, y2 = 200         };         layoutroot.children.add(line);     } 

i've tried putting layoutroot..add call before setvalue/setleft doesn't seem make difference.

try :

         this.layoutroot.children.add(r);         canvas.setleft(r, 100);         canvas.settop(r, 100);  

rather than:

         canvas.setleft(r, 100);         canvas.settop(r, 100);         this.layoutroot.children.add(r); 

update : got fixed since in xaml default grid tag layoutroot. after changing canvas tag , no longer gets stuck.