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using Xamarin.Forms.CustomAttributes;
using Xamarin.Forms.Internals;
using System.Linq;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System;
using System.Diagnostics;
#if UITEST
using Xamarin.UITest;
using NUnit.Framework;
#endif
namespace Xamarin.Forms.Controls.Issues
{
[Preserve(AllMembers = true)]
[Issue(IssueTracker.Bugzilla, 56896, "ListViews for lists with many elements regressed in performance on iOS", PlatformAffected.iOS)]
public class Bugzilla56896 : TestContentPage
{
const string Instructions = "The number in blue is the number of constructor calls. The number in red is the initial load time in milliseconds.";
const string ConstructorCountId = "constructorCount";
const string TimeId = "time";
[Preserve(AllMembers = true)]
class MyViewModel : INotifyPropertyChanged
{
int _constructorCallCount;
public int ConstructorCallCount
{
get { return _constructorCallCount; }
set
{
_constructorCallCount = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
[Preserve(AllMembers = true)]
class Fizz : ViewCell
{
readonly MyViewModel _vm;
Label myLabel;
public Fizz(MyViewModel vm)
{
_vm = vm;
vm.ConstructorCallCount++;
Height = 30;
myLabel = new Label { Text = "fizz" };
View = myLabel;
}
~Fizz()
{
_vm.ConstructorCallCount--;
}
}
[Preserve(AllMembers = true)]
class Buzz : ViewCell
{
readonly MyViewModel _vm;
Label myLabel;
public Buzz(MyViewModel vm)
{
_vm = vm;
vm.ConstructorCallCount++;
Height = 50;
myLabel = new Label { Text = "buzz" };
View = myLabel;
}
~Buzz()
{
_vm.ConstructorCallCount--;
}
}
[Preserve(AllMembers = true)]
class Fizzbuzz : ViewCell
{
readonly MyViewModel _vm;
Label myLabel;
public Fizzbuzz(MyViewModel vm)
{
_vm = vm;
vm.ConstructorCallCount++;
Height = 150;
myLabel = new Label { Text = "fizzbuzz" };
View = myLabel;
}
~Fizzbuzz()
{
_vm.ConstructorCallCount--;
}
}
[Preserve(AllMembers = true)]
class Number : ViewCell
{
readonly MyViewModel _vm;
Label myLabel;
public Number(MyViewModel vm)
{
_vm = vm;
vm.ConstructorCallCount++;
Height = 44;
myLabel = new Label();
myLabel.SetBinding(Label.TextProperty, ".");
View = myLabel;
}
~Number()
{
_vm.ConstructorCallCount--;
}
}
class MyDataTemplateSelector : DataTemplateSelector
{
DataTemplate _fizzbuzz;
DataTemplate _fizz;
DataTemplate _buzz;
DataTemplate _number;
public MyDataTemplateSelector(MyViewModel vm)
{
_fizzbuzz = new DataTemplate(() => new Fizzbuzz(vm));
_fizz = new DataTemplate(() => new Fizz(vm));
_buzz = new DataTemplate(() => new Buzz(vm));
_number = new DataTemplate(() => new Number(vm));
}
protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
{
int number = (int)item;
if (number % 15 == 0)
return _fizzbuzz;
else if (number % 5 == 0)
return _buzz;
else if (number % 3 == 0)
return _fizz;
else
return _number;
}
}
Label _timeLabel = new Label { TextColor = Color.Purple, AutomationId = TimeId };
Stopwatch _timer = new Stopwatch();
ListView _listView;
protected override void Init()
{
_timer.Start();
var vm = new MyViewModel();
BindingContext = vm;
var label = new Label { TextColor = Color.Blue, AutomationId = ConstructorCountId };
label.SetBinding(Label.TextProperty, nameof(vm.ConstructorCallCount));
_listView = new ListView(ListViewCachingStrategy.RecycleElement)
{
HasUnevenRows = true,
// Set the RowHeight to enable optimal performance and minimal constructor calls.
// It will still use the specified Cell heights on final measure.
// Note, however, that doing this negates the fix for Bugzilla 43313, so if user expects
// to add items to the bottom of this list and scroll smoothly, user should omit the RowHeight
// and rely solely on the Cell heights. This will cause each row to be constructed at least once,
// but it will allow the ListView to estimate the height properly for smooth scrolling.
// Also note that performance will degrade if the first cell does not have a specified height or
// if most of the cells do not have a specified height. It is recommended to specify a height on all
// or none of the cells when possible.
RowHeight = 50,
ItemsSource = Enumerable.Range(1, 5001),
ItemTemplate = new MyDataTemplateSelector(vm)
};
Content = new StackLayout { Children = { new Label { Text = Instructions }, label, _timeLabel, _listView } };
}
protected override void OnAppearing()
{
base.OnAppearing();
_timer.Stop();
_timeLabel.Text = _timer.ElapsedMilliseconds.ToString();
_timer.Reset();
}
#if UITEST
[Test]
public void Bugzilla56896Test()
{
RunningApp.WaitForElement(q => q.Marked(Instructions));
var count = int.Parse(RunningApp.Query(q => q.Marked(ConstructorCountId))[0].Text);
Assert.IsTrue(count < 100); // Failing test makes ~15000 constructor calls
var time = int.Parse(RunningApp.Query(q => q.Marked(TimeId))[0].Text);
Assert.IsTrue(count < 2000); // Failing test takes ~4000ms
}
#endif
}
}
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