FlowListView - questions about dltoolkit.forms.controls HOT 25 CLOSED

DataTemplateSelector derives from DataTemplate. So I think you can just have one property called DataTemplate FlowItemTemplate.
Xamarin Forms ListView does it like this for the ItemTemplate property: https://blog.xamarin.com/customizing-list-view-cells-xamarin-forms-datatemplateselector/

Optionally, if you want to offer the ability to select based on item's index, you could have a FlowItemTemplateSelector which looks like this:

public abstract class FlowItemTemplateSelector : DataTemplate
{
         public abstract DataTemplate SelectTemplate(int index, object item);
}

I am not sure about having both FlowColumnCount and FlowAutoColumnCount. Maybe have just int? FlowColumnCount which by default is null, meaning control auto computes the number of columns based on FlowLisView's width and flow item's width.
I would change FlowColumnDefaultMinimumWidth to just int? FlowColumnWidth. If it's null and you need item width, use the item's MinimumWidth.

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well, you could still keep the FlowColumnTemplateSelector, something like this:

<dltoolkit:FlowListView.FlowColumnsTemplateSelectors>
                    <dltoolkit:FlowColumnTemplateSelector Template="{StaticResource MyTemplate1}" />
                     <dltoolkit:FlowColumnTemplateSelector Template="{StaticResource MyTemplate2}" />
</dltoolkit:FlowListView.FlowColumnsTemplateSelectors>

not sure this is the cleanest way..

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<flv:FlowListView FlowColumnCount="3" FlowItemsSource="{Binding Items}" 
    SeparatorVisibility="None" HasUnevenRows="false"
    FlowItemTappedCommand="{Binding ItemTappedCommand}" FlowLastTappedItem="{Binding LastTappedItem}">

    <flv:FlowListView.FlowColumnTemplate>
        <DataTemplate>
            <Label HorizontalOptions="Fill" VerticalOptions="Fill" 
                XAlign="Center" YAlign="Center" Text="{Binding Title}"/>
        </DataTemplate>
    </flv:FlowListView.FlowColumnTemplate>

</flv:FlowListView>     

It also supports DataTemplateSelector. Testers are welcome.

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Hi @opcodewriter,

Can I specify a DataTemplate for the cell?

Yes, FlowColumnTemplateSelector is just a sample implementation of FlowColumnTemplateSelector. You can create your own:

    public class CustomAdvancedTemplateSelector : FlowColumnTemplateSelector
    {
        public override Type GetColumnType(object bindingContext)
        {
            // YOUR CUSTOM LOGIC HERE

            if (bindingContext == null)
                return typeof(ContentView);

            return typeof(FlowListViewExpandCell);
        }
    }

If I change the width and height of a cell, does it refresh correctly?

FlowListView is ListView derivative, so the same behavior is expected as in ListView. Basically it does layout of columns in one ViewCell with usage of AbsoluteLayout (for performance reasons).

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@daniel-luberda Thanks but, for the 1st question, it won't work

I need to be able to give a DataTemplate not a Type. Right now, you use the Type to create an instance of the view by calling Activator.CreateInstance(columnTypes[i])

I realized this is actually not possible, I have to modify the code of the library to use DataTemplate.

In my opinion, supporting DataTemplate is important for people who use DataTemplate defined in XAML, instead of creating the cell View manually in code.

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I also wanted to use DataTemplate but finally because of performance issues, I didn't. Please notice, DataTemplate always creates a new View instance. That's not what we want here (view reusing, etc). If you have any idea how to overcome this, please let me know.

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BTW: You can still define Views in XAML, the only difference is, it's a separate file.

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You also create a new instance now, so using a DataTemplate would be the same thing.

But yes, you would need to modify RowLayoutChanged to check for modifications:
just need to cache the DataTemplates.

Something like this (see comments for the new code):

public class FlowListViewInternalCell : ViewCell
{
        readonly IList<DataTemplate> _flowColumnDataTemplates;`

        protected override void OnBindingContextChanged()
        {      
              ....
            else // RECREATE COLUMNS
            {
                if (_rootLayout.Children.Count > 0)
                {
                    _rootLayout.Children.Clear();
                    _flowColumnDataTemplates.Clear();  // clear the data templates
                }

                for (int i = 0; i < containerCount; i++)
                {
                    var view = (View)columnTypes[i].CreateContent();

                    _flowColumnDataTemplates.Add(columnTypes[i]);  // save the data templates

                    view.GestureRecognizers.Add(new TapGestureRecognizer()
                    {
                        Command = new Command(async (obj) =>
                        {
                            await ExecuteTapGestureRecognizer(view);
                        })
                    });

                    SetBindingContextForView(view, container[i]);
                    AddViewToLayout(view, containerCount, i);
                }
            }
              ....
        }

        private bool RowLayoutChanged(int containerCount, IList<DataTemplate> columnTypes)
        {
            // Check if desired number of columns is equal to current number of columns
            if (_rootLayout.Children.Count != containerCount)
            {
                return true;
            }
            else
            {
                // Check if desired column view types are equal to current columns view types
                for (int i = 0; i < containerCount; i++)
                {
                    if (_flowColumnDataTemplates[i] != columnTypes[i])
                    {
                        return true;
                    }

                    //if (_rootLayout.Children[i] != columnTypes[i])
                    //{
                    //    return true;
                    //}
                }
            }

            return false;
        }
} 

from dltoolkit.forms.controls.

public abstract class FlowColumnTemplateSelector
{
    public abstract DataTemplate GetColumnType(object bindingContext);
}

from dltoolkit.forms.controls.

You also create a new instance now, so using a DataTemplate would be the same thing.

Not exactly. I don't create instances every time (they're reused if possible, eg. view type didn't change). Take a look here: https://github.com/daniel-luberda/DLToolkit.Forms.Controls/blob/master/FlowListView/DLToolkit.Forms.Controls.FlowListView/FlowListViewInternalCell.cs#L253-L254

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Yes, I know. You can achieve same thing with DataTemplate, you just need to save them in the FlowListViewInternalCell so you can compare them with the new ones in the RowLayoutChanged

See my code.

I actually did this and works great.

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I didn't see your code yet as I'm not at home. Do you mean comparing DataTemplate type? If it's possible, we could Obsolete old template selectors and create new DataTemplate based. But:

FlowListView need a List of DataTemplates - I had some problems with it (it wasn't supported by XAML compiler). I don't know if anything changed in that matter.

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What problems did you have exactly? Maybe I can help.

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This works:

<DataTemplate>
    <ContentView/>
</DataTemplate>

This doesn't:

<DataTemplates>
    <DataTemplate>
        <ContentView/>
    </DataTemplate>
    <DataTemplate>
        <ContentView/>
    </DataTemplate>
</DataTemplates>

We need multiple DataTemplate definitions. But I didn't test it on recent XF versions.

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@opcodewriter I have an idea:

• DataTemplate FlowColumnTemplate property (not a list, just a single one)
• int FlowColumntCount property which will be used when FlowAutoColumnCount is disabled
• Multiple templates can be solved with DataTemplateSelector
• That way, we still have full XAML syntax support

What do you think?

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@jamesl77 These are really nice suggestions. I'll implement it and obsolete old properties (they'll still work for compatibility).

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Compatibility is an issue, but in the same time keeping the obsolete code and mixing with new code, just for the sake of compatibility, I'm not sure is a good thing on the long run. At some point you need to get rid of it, there's a reason why it's obsolete I assume :)
Why not go to a major version of the library? The library right now is stable enough I guess? So people who use your library at current version are fine with it.

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Nuget 2.0.0-alpha1 released. I also created new samples project:

https://github.com/daniel-luberda/DLToolkit.Forms.Controls/blob/master/Samples/DLToolkitControlsSamples/SamplesFlowListView/SimplePage.xaml

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So which way did you go in the end? Mixing old and new?

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For now, no compatibility. But it's very easy to add as we only need to add old properties and translate them to the new DataTemplate based code. It won't have any impact for internal code. What do you think?

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I'm for clean code. Like I said before, the library is small, and pretty stable. No reason to keep deprecated code.

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Please, add compatibility in the new version. Old code works well.

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@3-50 using current released version still works and will still work. I can't speak in the name of @daniel-luberda but I think if any critical bug will appear it's still going to be fixed in current released version.

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@3-50 The new API allows you to use the same source data which is used in a Xamarin.Forms ListView, just with column support. I also allows dev to use DataTemplates which devs are used to. Old one is quite stable, I don't know of any issues with it. If some issues will be found in old version, I'll publish bug fixes release, so don't worry.

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@opcodewriter, @daniel-luberda Thank you for your answer.

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