xamarin.forms - What does x:Double mean for a Xamarin Button? -

my code has:

<button x:name="correctbutton" heightrequest="60" horizontaloptions="fillandexpand" verticaloptions="startandexpand">    <button.fontsize>       <onplatform x:typearguments="x:double" ios="25" android="20" />    </button.fontsize> </button> 

can explain x:double means

i have broken down comments in xaml.

<!-- here button declared, note how see x:name here --> <button x:name="correctbutton" heightrequest="60" horizontaloptions="fillandexpand" verticaloptions="startandexpand">    <!-- besides giving properties control, in case button, attributes, can set them adding them child nodes. happens fontsize here -->    <button.fontsize>       <!-- not setting fontsize here, letting value dependent on platform running on. ios value 25, android 20. -->       <onplatform x:typearguments="x:double" ios="25" android="20" />    </button.fontsize> </button> 

now, x:double needed tell onplatform tag type should provide it, can x:int32 or other type if needed. because provide string values in onplatform tag, needs know type has cast value.

remember pointed out x:name property. x shorthand namespace find type. if @ page declaration, have attribute like: xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml", see how x declared here? why x needed in front, tell xaml double type can found in http://schemas.microsoft.com/winfx/2009/xaml namespace, abbreviated x default.

note onplatform tag in way deprecated of xamarin.forms 2.3.4. should use such:

<button x:name="correctbutton" heightrequest="60" horizontaloptions="fillandexpand" verticaloptions="startandexpand">    <button.fontsize>        <onplatform x:typearguments="x:double" x:key="windowbackgroundtable">            <on platform="android" value="20" />            <on platform="ios" value="25" />        </onplatform>      </button.fontsize> </button>