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Which Item is user focused in listview xamarin forms

I am a student learning xamarin forms, I am trying to create a basic chat app in this I want to know how to get position of current item in listview that's user watching. When a new message received i want to know if user is at bottom or not if at bottom focus the new and if not at the bottom then just add not by adding focus to it.

you get the selected item from the Xamarin.Forms.ListView.SelectedItem property of your ListView.
If your ListView.ItemSource is of a type that allows using IndexOf you can now do something like
int position = (yourlistview.ItemSource as ObservableCollection<your type>).IndexOf(yourlistview.SelectedItem)
Update:
ok I think i understood what you want.
In most cases more than one item is currently shown when using a listview. So their exists not a single index
but i think you just want to know if the last item of the list is visible/the user has scrolled to the end?
If so ListView has an ItemAppearing event. I use it for example to load more data from an websource if the user scrolled through the first 100 items.
You could do something like this
listview.ItemAppearing += listviewItemAppearing;
listview.ItemDisappearing += listviewItemDisappearing;
bool m_scrolledToEnd;
private void listviewItemDisappearing(object sender, ItemVisibilityEventArgs e)
{
if(e.Item == yourlastiem)
m_scrolledToEnd = false;
}
private void listviewItemAppearing(object sender, ItemVisibilityEventArgs e)
{
if(e.Item == yourlastiem)
m_scrolledToEnd = true;
}
if you realy need to know if a specific index is shown you could create a List<int> m_idxlist;
and in the appearing event add the index of the item to the list
and in the disappearing event remove the index of the item from the list.
Then you will have a list where all indexes of the items currently shown are stored.

From the Documentation
ListView supports selection of one item at a time. Selection is on by
default. When a user taps an item, two events are fired: ItemTapped
and ItemSelected. Note that tapping the same item twice will not fire
multiple ItemSelected events, but will fire multiple ItemTapped
events. Also note that ItemSelected will be called if an item is
deselected.
To detect selecting an item, you can add a method, onSelection:
void OnSelection (object sender, SelectedItemChangedEventArgs e)
{
if (e.SelectedItem == null) {
return; //ItemSelected is called on deselection, which results in SelectedItem being set to null
}
DisplayAlert ("Item Selected", e.SelectedItem.ToString (), "Ok");
//((ListView)sender).SelectedItem = null; //uncomment line if you want to disable the visual selection state.
}
To disable selection just set the selectedItem to null:
SelectionDemoList.ItemSelected += (sender, e) => {
((ListView)sender).SelectedItem = null;
};

Remove something added by a particular event - c#

I have a piece of code that will add the selected item of a combobox to a listbox when a checkbox is checked. I would like to remove that selected item to be removed from the listbox when the checkbox is unchecked.
My problem is I cant simply repeat the code for removal to be the same as add because the combobox selection will different or empty when unchecked.
This is how it currently looks:
private void CBwasher_CheckedChanged(object sender, EventArgs e)
{
if (checkBox1.Checked == true)
{
listBox2.Items.Add(comboBox1.SelectedItem);
}
if (checkBox1.Checked == false)
{
listBox2.Items.Remove(comboBox1.SelectedItem);
}
So I need a way of removing whatever was added by that check change instead of removing the selected index of the combobox. Please consider that there may be multiple lines in the listbox added by multiple different checkboxes.

You simply need to store the added item and remove it.
private object addedItem;
private void CBwasher_CheckedChanged(object sender, EventArgs e)
{
if (checkBox1.Checked)
{
addedItem = comboBox1.SelectedItem;
listBox2.Items.Add(addedItem);
}
else
{
listBox2.Items.Remove(addedItem);
}
}
You may also need to check SelectedItem is null before adding/removing the item.

Focusing on the part where you said there might be multiple different checkboxes,
you need to store one item per checkbox.
You can write your own child class of the checbox control to add this feature, or simply use the Tag property.
You can also indicate which checkbox is linked to which combobox in the same way. Either child class or use the Tag property.
In my example, I'll assume you've referenced the combobox from the checkbox using the Tag property.
You can do it manually like this
checkBox1.Tag = comboBox1;
or hopefully you can automate it if you are generating these on the fly.
Here is the general idea of how the checkbox event should look.
The event is is utilising the sender argument, which means you should hook up all your checkboxes CheckedChanged events to this one handler. No need to create separate handlers for each.
private void CBwasher_CheckedChanged(object sender, EventArgs e)
{
var checkBox = (CheckBox)sender;
var comboBox = (ComboBox)checkBox.Tag;
if (checkBox.Checked && comboBox.SelectedItem != null)
{
listBox2.Items.Add(comboBox.SelectedItem);
comboBox.Tag = comboBox.SelectedItem;
}
if (!checkBox.Checked && comboBox.Tag != null)
{
listBox2.Items.Remove(comboBox.Tag);
}
}

Unable to get LIstBoxItem from ListBox

I am unable to get ListBoxItem from ListBox. I have created ListBox dynamically; it is not in XAML. I just set ItemsSource and I have values in all the items but cannot access/convert each item as ListBoxItem.
for (int i = 0; i < listBox.Items.Count; i++)
{
ListBoxItem item = (ListBoxItem)listBox.ItemContainerGenerator.ContainerFromItem(listBox.Items[i]);
// item is null after above statement
}
Note: I just checked 'listBox.ItemContainerGenerator.Status' . listBox.ItemContainerGenerator.Status is 'notStarted'.
What to do now?

It sounds like you are not giving WPF enough time to render the <ListBoxItem> objects before calling your method.
A common way of accessing the ListBoxItems right after its Items property is set is to use the ItemContainerGenerator.StatusChanged event, like this:
void MyConstructor()
{
listBox.ItemsSource = someCollection;
listBox.ItemContainerGenerator.StatusChanged +=
ItemContainerGenerator_StatusChanged;
}
void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)
{
// If containers have been generated
if (listBox.ItemContainerGenerator.Status ==
System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated)
{
// Remove event
listBox.ItemContainerGenerator.StatusChanged -=
ItemContainerGenerator_StatusChanged;
// Do whatever here
foreach(var item in listBox.Items)
{
var item = (ListBoxItem)listBox.ItemContainerGenerator.ContainerFromItem(item);
// do whatever you want with the item
}
}
}
WPF runs code at different DispatcherPriorities. Code run in the constructor or on load is run at Normal priority, while the generation of ListBoxItem objects doesn't occur until Render priority, which runs after all Normal priority items have finished running.
You could alternatively use the Dispatcher to run your code at a later dispatcher priority than Render as well.

Why are you casting the listbox to a listboxitem?
Here is a simular question about getting the selected items
listbox selected items in winform
You should be able to get the item by it's index
ListBox1.Items.Item(index)

WPF: Raise an Event when Item is added in ListView

I am working on WPF and I am using a ListView, and I need to fire an event when an item is added to it. I have tried this:
var dependencyPropertyDescriptor = DependencyPropertyDescriptor.FromProperty(ItemsControl.ItemsSourceProperty, typeof(ListView));
if (dependencyPropertyDescriptor != null)
{
dependencyPropertyDescriptor.AddValueChanged(this, ItemsSourcePropertyChangedCallback);
}
.....
private void ItemsSourcePropertyChangedCallback(object sender, EventArgs e)
{
RaiseItemsSourcePropertyChangedEvent();
}
But It seems to be working only when the entire collection is changed, I have read this post: event-fired-when-item-is-added-to-listview, but the best answer applies for a listBox only. I tried to change the code to ListView but I wasnt able to do that.
I hope You can help me. Thank you in advance.

Note this only works for a WPF Listview!
After some research I have found the answer to my question and It's really easy:
public MyControl()
{
InitializeComponent();
((INotifyCollectionChanged)listView.Items).CollectionChanged += ListView_CollectionChanged;
}
private void ListView_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
// scroll the new item into view
listView.ScrollIntoView(e.NewItems[0]);
}
}
Actually, the NotifyCollectionChangedAction enum allows your program to inform you about any change such as: Add, Move, Replace, Remove and Reset.

Note: This solution was meant for a WinForms ListView.
In my case I ended up coming to a fork in the road with 2 choices...
(1) Create a custom ListView control that inherits a ListView's class. Then add a new event to be raised when any item is added, deleted, or ListView is cleared. This path seemed really messy and long. Not to mention the other big issue that I would need to replace all my original ListViews with the newly created Custom ListView control. So I passed on this!
(2) With every add, delete, or clear call to the listview I also called another function simulating the CollectionChanged event.
Create the new event like function...
private void myListViewControl_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
//The projects ListView has been changed
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
MessageBox.Show("An Item Has Been Added To The ListView!");
break;
case NotifyCollectionChangedAction.Reset:
MessageBox.Show("The ListView Has Been Cleared!");
break;
}
}
Add an item to the ListView elsewhere...
ListViewItem lvi = new ListViewItem("ListViewItem 1");
lvi.SubItems.Add("My Subitem 1");
myListViewControl.Items.Add(lvi);
myListViewControl_CollectionChanged(myListViewControl, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, lvi, lvi.Index));
Clear the ListView elsewhere...
myListViewControl.Items.Clear();
myListViewControl_CollectionChanged(myListViewControl, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));

Listbox items at the bottom were not automatically selected

I have this subtle program regarding the behavior of listbox. My listbox is binded with an observable list in the viewmodel. There are 2 ways in addding an item in the listbox. First is ADD a single item then that item would be selected directly. This works fine.
The second way was LOAD which by its name will be adding more than 1 item in the lisbox. Now the problem is when loading items more than the listbox can accomodate in the view, those items that are not in view (items at the bottom thus need to be scrolled in order for it to be viewed) was not automatically selected...
Only the items that are by default viewed are the ones selected:
private void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)
{
if (listBoxAddresses.ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated) return;
for (int i = 0; i < TestSetting.DeviceSettings.Count; i++)
{
ListBoxItem myListBoxItem = (ListBoxItem)(listBoxAddresses.ItemContainerGenerator.ContainerFromItem(TestSetting.DeviceSettings[i]));
if (myListBoxItem != null)
{
myListBoxItem.IsSelected = true;
}
}
listBoxAddresses.ItemContainerGenerator.StatusChanged -= ItemContainerGenerator_StatusChanged;
}
I wonder if this is just a natural behavior for listbox.

I just realize this now...setting my listbox to :
VirtualizingStackPanel.IsVirtualizing="False"
did all the trick. Thanks to Dr.WPF for the idea. Though there are consequences for turning off virtualization (performance) but it won't matter that much.