wpf - Redundant converter calls when using Triggers to determine value -

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i noticed xaml markup wasting resources doing conversions not supposed do. e.g. have following style acts switch:

<style targettype="{x:type image}">     <style.triggers>         <datatrigger binding="{binding isdownloaded}" value="true">             <setter property="source"                     value="{binding data, converter={staticresource bytearraytobitmapimageconv}}"/>         </datatrigger>         <datatrigger binding="{binding isdownloaded}" value="false">             <setter property="source"                     value="{binding url, converter={staticresource urltobitmapimageconv}}"/>         </datatrigger>     </style.triggers> </style>

obviously should either download image if has not been cached or turn raw data bitmapimage. problem both cases have taken place @ least once both converters called when datacontext changes, irrespectively of value isdownloaded has. either display converted image still download independendly in background or download image , try convert null (the data) bitmapimage.

setting binding mode onetime did not sadly.

i looking clean way avoid occurs multiple times in application. e.g. here:

<style targettype="contentcontrol">     <setter property="content" value="{staticresource contentnothingselected}"/>     <style.triggers>         <datatrigger binding="{binding source={x:static local:app.settings}, path=displaymode_current}"                      value="description">             <setter property="content" value="{staticresource descriptionviewer}"/>         </datatrigger>         <datatrigger binding="{binding source={x:static local:app.settings}, path=displaymode_current}"                      value="webpage">             <setter property="content" value="{staticresource webpageviewer}"/>         </datatrigger>         <datatrigger binding="{binding source={x:static local:app.settings}, path=displaymode_current}"                      value="media">             <setter property="content" value="{staticresource mediaviewer}"/>         </datatrigger>     </style.triggers> </style>

even if display mode set media or description application navigate corresponding site in background, wasting resources , throwing occasional out of place javascript-error notifications.

i did of in code remodelled more declarative , keep way, appreciated.

you reconsider using triggers , instead use custom control , visual state manager. put logic of downloading , caching , converting images in custom control , set appropriate states. it's hard give example without more xaml i'm afriad.


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