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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Threading.Tasks;
using Xamarin.Forms.Internals;
namespace Xamarin.Forms.Controls
{
[Preserve(AllMembers = true)]
public class CellForceUpdateSizeGalleryPage : NavigationPage
{
[Preserve(AllMembers = true)]
public class MyViewCell : ViewCell
{
Label _Label = new Label();
VariableHeightItem _DataItem => BindingContext as VariableHeightItem;
public MyViewCell()
{
_Label.SetBinding(Label.TextProperty, nameof(_DataItem.Text));
_Label.PropertyChanged += UpdateCell;
View = new StackLayout { Children = { _Label } };
}
void UpdateCell(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == Label.TextProperty.PropertyName)
{
ForceUpdateSize();
}
}
}
[Preserve(AllMembers = true)]
public class MyImageCell : ImageCell
{
VariableHeightItem _DataItem => BindingContext as VariableHeightItem;
public MyImageCell()
{
SetBinding(TextProperty, new Binding(nameof(_DataItem.Text)));
PropertyChanged += UpdateCell;
}
void UpdateCell(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == ImageCell.TextProperty.PropertyName)
{
(sender as ImageCell).Height += 100;
ForceUpdateSize();
}
}
}
[Preserve(AllMembers = true)]
public class MyTextCell : TextCell
{
VariableHeightItem _DataItem => BindingContext as VariableHeightItem;
public MyTextCell()
{
SetBinding(TextProperty, new Binding(nameof(_DataItem.Text)));
PropertyChanged += UpdateCell;
}
void UpdateCell(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == TextCell.TextProperty.PropertyName)
{
(sender as TextCell).Height += 100;
ForceUpdateSize();
}
}
}
[Preserve(AllMembers = true)]
public class MyEntryCell : EntryCell
{
VariableHeightItem _DataItem => BindingContext as VariableHeightItem;
public MyEntryCell()
{
SetBinding(TextProperty, new Binding(nameof(_DataItem.Text)));
PropertyChanged += UpdateCell;
}
void UpdateCell(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == EntryCell.TextProperty.PropertyName)
{
(sender as EntryCell).Height += 100;
ForceUpdateSize();
}
}
}
[Preserve(AllMembers = true)]
public class MySwitchCell : SwitchCell
{
VariableHeightItem _DataItem => BindingContext as VariableHeightItem;
public MySwitchCell()
{
SetBinding(TextProperty, new Binding(nameof(_DataItem.Text)));
PropertyChanged += UpdateCell;
}
void UpdateCell(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == SwitchCell.TextProperty.PropertyName)
{
(sender as SwitchCell).Height += 100;
ForceUpdateSize();
}
}
}
public class MyPage<T> : ContentPage where T : Cell
{
private List<VariableHeightItem> _DataSource;
public MyPage(ListViewCachingStrategy strategy)
{
_DataSource = Enumerable.Range(0, 10).Select(n => new VariableHeightItem()).ToList();
var listView = new ListView(strategy) { HasUnevenRows = true, ItemsSource = _DataSource, ItemTemplate = new DataTemplate(typeof(T)) };
var button = new Button { Text = "Click me" };
button.Clicked += async (sender, e) =>
{
for (int i = 0; i < _DataSource.Count; i++)
{
var target = _DataSource[i];
if (Device.RuntimePlatform == Device.iOS)
{
if (typeof(T) == typeof(MyViewCell))
target.Text = "I am an exceptionally long string that should cause the label to wrap, thus increasing the size of the cell such that the entirety of the string is readable by human eyes. Hurrah.";
else if (strategy == ListViewCachingStrategy.RetainElement)
target.Text = "Look, I'm taller!";
else
target.Text = $"I'm only taller in {ListViewCachingStrategy.RetainElement} mode. :(";
}
else
{
if (typeof(T) == typeof(MyViewCell))
target.Text = "I am an exceptionally long string that should cause the label to wrap, thus increasing the size of the cell such that the entirety of the string is readable by human eyes. Hurrah.";
else
target.Text = "Look, I'm taller!";
}
await Task.Delay(1000);
}
};
Content = new StackLayout { Children = { button, listView } };
Title = $"{typeof(T).Name} {strategy}";
}
}
class VariableHeightItem : ViewModelBase
{
public VariableHeightItem()
{
Text = "This is a line of text.";
}
public string Text
{
get { return GetProperty<string>(); }
set { SetProperty(value); }
}
}
public CellForceUpdateSizeGalleryPage()
{
var stackLayout = new StackLayout();
stackLayout.Children.Add(GetButton<MyViewCell>(ListViewCachingStrategy.RetainElement));
stackLayout.Children.Add(GetButton<MyImageCell>(ListViewCachingStrategy.RetainElement));
stackLayout.Children.Add(GetButton<MyEntryCell>(ListViewCachingStrategy.RetainElement));
stackLayout.Children.Add(GetButton<MyTextCell>(ListViewCachingStrategy.RetainElement));
stackLayout.Children.Add(GetButton<MySwitchCell>(ListViewCachingStrategy.RetainElement));
stackLayout.Children.Add(GetButton<MyViewCell>(ListViewCachingStrategy.RecycleElement));
stackLayout.Children.Add(GetButton<MyImageCell>(ListViewCachingStrategy.RecycleElement));
stackLayout.Children.Add(GetButton<MyEntryCell>(ListViewCachingStrategy.RecycleElement));
stackLayout.Children.Add(GetButton<MyTextCell>(ListViewCachingStrategy.RecycleElement));
stackLayout.Children.Add(GetButton<MySwitchCell>(ListViewCachingStrategy.RecycleElement));
Navigation.PushAsync(new ContentPage { Content = stackLayout });
}
Button GetButton<T>(ListViewCachingStrategy strategy) where T : Cell
{
return new Button
{
Text = $"{typeof(T).Name} {strategy}",
Command = new Command(async () => await Navigation.PushAsync(new MyPage<T>(strategy)))
};
}
}
}
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