c# - Performance lag in scrollTo function for LongListSelector in WP8? -

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to demonstrate problem here code behind code

public partial class mainpage : phoneapplicationpage {     observablecollection<abc> listtest = new observablecollection<abc>();     // constructor     public mainpage()     {         initializecomponent();          (int = 0; < 50; i++)         {             abc conv = new abc(string.format("test:{0}", i));             listtest.add(conv);         }         testlls.itemssource = listtest;     }      private void button_tap_1(object sender, system.windows.input.gestureeventargs e)     {         testlls.scrollto(listtest[listtest.count - 1]);     }      private void titlepanel_tap_1(object sender, system.windows.input.gestureeventargs e)     {         stopwatch st = stopwatch.startnew();          testlls.scrollto(listtest[listtest.count - 1]);         st.stop();         debug.writeline("tttt:", st.elapsedmilliseconds);     }      class abc     {         private string _name;          public abc(string aa)         {             this._name = aa;         }          public string name         {                         {                 return _name;             }         }          public visibility groupmembervisibility         {                         {                 return visibility.collapsed;             }         }     } }

xaml code

     <stackpanel x:name="titlepanel" grid.row="0" margin="12,17,0,28" tap="titlepanel_tap_1">         <textblock text="my application" style="{staticresource phonetextnormalstyle}" margin="12,0"/>         <textblock text="page name" margin="9,-7,0,0" style="{staticresource phonetexttitle1style}"/>     </stackpanel>      <!--contentpanel - place additional content here-->     <grid x:name="contentpanel" grid.row="1" margin="12,0,12,0">         <phone:longlistselector name="testlls" virtualizingstackpanel.virtualizationmode="standard" >             <phone:longlistselector.itemtemplate>                 <datatemplate x:name="dtrecievedbubbletext" >                     <grid x:name="layoutroot" background="transparent" margin="24 0 0 14"  horizontalalignment="left">                          <grid.rowdefinitions>                             <rowdefinition height="14" />                             <rowdefinition height="auto" />                         </grid.rowdefinitions>                         <grid grid.row="1">                             <grid.rowdefinitions>                                 <rowdefinition height="auto" />                                 <rowdefinition height="auto" />                                 <rowdefinition height="auto" />                             </grid.rowdefinitions>                             <grid.columndefinitions>                                 <columndefinition width="auto"/>                             </grid.columndefinitions>                             <rectangle grid.rowspan="3" fill="{binding bubblebackgroundcolor}" />                             <textblock text="test" visibility="{binding groupmembervisibility}" fontsize="22" fontfamily="segoe wp semibold" margin="12, 12, 0, 0"  />                             <textblock grid.row="2" text="{binding name}" horizontalalignment="right" margin="0,0,12,6" fontsize="18" />                         </grid>                     </grid>                 </datatemplate>             </phone:longlistselector.itemtemplate>         </phone:longlistselector>      </grid>

on tapping header long list selector containg elemnts scrolls bottom. when value of elements changed 30-50-100 elements time observed 20ms, 744ms, 815ms. testing done nokia lumia 620.

in sample, item template simple in real scenario item templates more complex. , time taken in scenario 1753ms 100 elements.

why such huge time difference. can improved in way?

has else observed this?

there workaround fix issue.

extract viewport lls , set viewport origin.

to extract viewport have add style in xaml

  <style x:name="llsmessagesstyle"  targettype="phone:longlistselector">         <setter property="background" value="transparent"/>         <setter property="template">             <setter.value>                 <controltemplate targettype="phone:longlistselector">                     <grid background="{templatebinding background}" d:designwidth="480" d:designheight="800">                         <visualstatemanager.visualstategroups>                             <visualstategroup x:name="scrollstates">                                 <visualstategroup.transitions>                                     <visualtransition generatedduration="00:00:00.5"/>                                 </visualstategroup.transitions>                                 <visualstate x:name="scrolling">                                     <storyboard>                                         <doubleanimation duration="0" to="1" storyboard.targetproperty="opacity" storyboard.targetname="verticalscrollbar"/>                                     </storyboard>                                 </visualstate>                                 <visualstate x:name="notscrolling"/>                             </visualstategroup>                         </visualstatemanager.visualstategroups>                         <grid margin="0">                             <viewportcontrol x:name="viewportcontrol" horizontalcontentalignment="stretch" verticalalignment="bottom" loaded="viewportloaded"/>                             <scrollbar x:name="verticalscrollbar" style="{staticresource chatthemescrollbarstyle}" opacity="0" margin="2 0 2 0" orientation="vertical" horizontalalignment="right" width="5" valuechanged="vscrollbar1_valuechanged"  />                         </grid>                     </grid>                 </controltemplate>             </setter.value>         </setter>     </style>

in code behind:

 viewportcontrol llsviewport;     private void viewportloaded(object sender, routedeventargs e)     {         llsviewport = sender viewportcontrol;     }   private void scrolltobottom()     {         if (llsviewport != null)             llsviewport.setviewportorigin(new system.windows.point(0, llsviewport.bounds.height));     }

in way can achieve desired functionality.


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