Xamarin Style staticresource binding - xaml

would it be possible to databind a static resource in Xamarin Forms?
Something like
Style="{StaticResource {Binding foo, StringFormat='SomeStyle{0}'}}"
Thanks

What you probably want is a Value Converter that handles locating the StaticResource for you. Full Microsoft Documentation here.
On your XAML element, you'd do something like this:
<Entry Style="{Binding foo, Converter={StaticResource FooToStyleConverter}}"/>
Your converter would work something like this:
public class FooToStyleConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var someValue = (string)value; // Convert 'object' to whatever type you are expecting
// evaluate the converted value
if (someValue != null && someValue == "bar")
return (Style)App.Current.Resources["StyleOne"]; // return the desired style
return (Style)App.Current.Resources["StyleTwo"];
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
// Usually unused, but inverse the above logic if needed
throw new NotImplementedException();
}
}
Lastly, set up your converter as a Static Resource in App.xaml (or as a local resource on the page) so your page can properly reference it
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:DataBindingDemos">
<ContentPage.Resources>
<ResourceDictionary>
<local:FooToStyleConverter x:Key="FooToStyleConverter" />
....

Related

How to translate Xamarin Xaml IValueConverter into C#?

Can you please help me translate this Xamarin xaml into c#?
BackgroundColor="{Binding IconColor, Converter={StaticResource LocalHexColorFromStringConverter}}"/>
Thanks!
You can translate it by MyBtn.SetBinding(Button.BackgroundColorProperty, "IconColor", BindingMode.OneTime, new LocalHexColorFromStringConverter()) ;
I make a test with Button's background color.
Button MyBtn = new Button();
MyBtn.Text = "test";
MyBtn.SetBinding(Button.BackgroundColorProperty, "IconColor", BindingMode.OneTime, new LocalHexColorFromStringConverter()) ;
Content = MyBtn;
Here is LocalHexColorFromStringConverter.cs
public class LocalHexColorFromStringConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return Color.FromHex((string)value);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return value;
}
}
Can I ask what the difference is between "new LocalHexColorFromStringConverter()" and "converter: LocalHexColorFromStringConverter()" ?
Do you mean "new LocalHexColorFromStringConverter()" and "converter: LocalHexColorFromStringConverter"?
If so, they are same, converter: LocalHexColorFromStringConverter is wirte type in Xaml , converter: is prefix, it explains the specific path of this class, If you want to call it from any pages, you need to write it in the App.xaml.
For example, you add add it in the App.xaml.
<?xml version="1.0" encoding="utf-8" ?>
<Application xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:converters="clr-namespace:OAuthGoogleDemo"
x:Class="OAuthGoogleDemo.App">
<Application.Resources>
<ResourceDictionary>
<converters:LocalHexColorFromStringConverter x:Key="HexColorFromStringConverter" />
</ResourceDictionary>
</Application.Resources>
</Application>
Then use it in the Mainpage.xaml with Converter={StaticResource HexColorFromStringConverter}}"

Type not found on XAML namespace

I am trying to access to method class from XAML file.
My class is on folder: project.Utils.
Adding on xaml Content Page:
xmlns:local="project.Utils"
I try to use myConverterMethod class inside Utils folder and use it as:
Converter={StaticResource myConverterMethod}
but error Type myConverterMethod not found in xmlns project.Utils.
Where is my fault?
You can use
xmlns:local="clr-namespace:project.Utils;assembly=project"
It is not possible to refer to a Method within a specific class but to a IValueConverter.
In order to achieve what you want, you need to define a class that implements IValueConverter:
public class IntToBoolConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return (int)value != 0;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return (bool)value ? 1 : 0;
}
}
Define the created converter in accessible scope: Page/View or Application. By scope I mean resources:
<ContentPage.Resources>
<ResourceDictionary>
<local:IntToBoolConverter x:Key="intToBool" />
</ResourceDictionary>
</ContentPage.Resources>
and finally consume the converter in the next way:
<Button Text="Search"
HorizontalOptions="Center"
VerticalOptions="CenterAndExpand"
IsEnabled="{Binding Source={x:Reference entry1},
Path=Text.Length,
Converter={StaticResource intToBool}}" />
Xamarin has a very nice documentation that will answer all your questions and it usually has a good code samples.

CheckBox binding to element issue in WP8.1

I have a simple XAML:
<CheckBox x:Name="chkShowGrid" IsThreeState="False" IsChecked="False">Show content</CheckBox>
<Grid Visibility="{Binding IsChecked, ElementName=chkShowGrid}">
<TextBlock>Some content goes here</TextBlock>
</Grid>
This XAML works well in WinRT Windows 8.1 application. When I trying it in WP8.1 application it works in designer (shows or hides grid depend of checkbox value), but not on the phone. Why?
UPDATE:
I have universal 8.1 app and if use converter then shows me exception:
error CS0012: The type 'Type' is defined in an assembly that is not
referenced. You must add a reference to assembly 'System.Runtime,
Version=4.0.10.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
Converter code:
class BoolConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
if (value == null) return false;
return (bool)value;
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException();
}
}
In XAML
<Page.Resources>
<local:BoolConverter x:Name="ThatsMyConverter"/>
</Page.Resources>
........
<Grid Visibility="{Binding IsChecked, ElementName=chkShowSettings,Converter={StaticResource ThatsMyConverter}}">
Your converter returns a boolean value and you are trying to assign a bool to Visibility which can only take Visible or Collapsed as possible values. Try returning Visibility from your converter instead of bool. That should work. For example in your converter:
if (value == null) return Visibility.Collapses;
var val = (value as bool);
if (val)
return Visibility.Visible;
else
return Visibility.Collapsed;

Binding to Element height Plus a value

I wanna bind my element height to another element height plus 20 pixel...
Is it possible to do such a thing?
<ScrollViewer Height="{Binding Height, ElementName=AnotherElement}">
Yes, by using a value converter
public class IncreaseByValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, string language)
{
var passedInValue = System.Convert.ToDouble(value);
var increaseByValue = System.Convert.ToDouble(parameter);
return passedInValue + increaseByValue;
}
public object ConvertBack(object value, Type targetType, object parameter, string language)
{
throw new NotImplementedException();
}
}
defined as a static resource somewhere in your resources:
<local:IncreaseByValueConverter x:Key="IncreaseByValueConverter" />
used like this:
<ScrollViewer Height="{Binding Height, ElementName=AnotherElement, Converter={StaticResource IncreaseByValueConverter}", ConverterParameter="20">
You'll probably want to handle the converter parameter better by using some try/catch code in the IncreaseByValueConverter.Convert method. For example, make the parameter optional, so if it's not passed in, use a default value, or something like that...

The resource "ResourceName" could not be resolved error in WP8

I'm seeing an error trying to use a custom converter in my WP8 app.
I defined my converter in a namespace: standrighthere.Utilities:
namespace standrighthere.Utilities
{
public class NonNullVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return value == null ? Visibility.Collapsed : Visibility.Visible;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
I then included it in the App.xaml manifest as so:
<Application.Resources>
<utilities:NonNullVisibilityConverter x:Key="NonNullVisibiltyConverter" />
</Application.Resources>
I then tried to use it in my phone application page like this:
<Button Visibility="{Binding Source={Binding User}, Converter={StaticResource ResourceKey=NonNullVisibilityConverter}}" />
However, it keeps giving the error:
Error 1 The resource "NonNonNullVisibilityConverter" could not be resolved.
I feel like I must be missing something really obvious here.
Looks like a simple typo. You called your converter "NonNullVisibiltyConverter" in the resources and NonNonNullVisibil*i*tyConverter in the binding.