ForceUpdateSize ListView issue on iOS

Question

I have a custom ListView using custom ViewCells with radio buttons. On clicking of each of the radio buttons the ListView dynamically resizes its height to hide/show a comment box.

On using ForceUpdateSize in iOS platform, the ListView performance slows down rapidly on clicking the radio buttons. The app eventually hangs and stops responding.

Is there an alternative solution to use instead of ForceUpdateSize to dynamically expand the ListView row at runtime?

Answer 1

Define a ViewCell Size Change event wherever you need to change your ViewCell size

public static event Action ViewCellSizeChangedEvent; 

In your case, it should be triggered by your radio button. Call it like this:

ViewCellSizeChangedEvent?.Invoke();

It will then use the ListView renderer to update the iOS TableView.

public class CustomListViewRenderer : ListViewRenderer
{
    public CustomListViewRenderer()
    {
        WhatEverContentView.ViewCellSizeChangedEvent += UpdateTableView;
    }

    private void UpdateTableView()
    {
        var tv = Control as UITableView;
        if (tv == null) return;
        tv.BeginUpdates();
        tv.EndUpdates();
    }
}

It should solve your performance problem while keep using your Xaml instead of creating a custom ViewCell which is not needed.

Answer 2

My solution is: Try to use custom renderer. When the button clicked, I use tableView.ReloadRows() to dynamically change the size of a cell.

Firstly, define a bool list whose items equal to Rows you want to show in the Source. I initialize its items with false at first time.

List<bool> isExpanded = new List<bool>();

public MyListViewSource(MyListView view)
{
    //It depends on how many rows you want to show.
    for (int i=0; i<10; i++) 
    {
        isExpanded.Add(false);
    }
}

Secondly, Construct the GetCell event(I just put a UISwitch in my Cell for testing) like:

public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
{

    MyListViewCell cell = tableView.DequeueReusableCell("Cell") as MyListViewCell;

    if (cell == null)
    {
        cell = new MyListViewCell(new NSString("Cell"));

        //This event is constructed in my Cell, when the switch's value changed it will be fired.
        cell.RefreshEvent += (refreshCell, isOn) =>
        {
            NSIndexPath index = tableView.IndexPathForCell(refreshCell);
            isExpanded[index.Row] = isOn;
            tableView.ReloadRows(new NSIndexPath[] { index }, UITableViewRowAnimation.Automatic);
        };
    }

    cell.switchBtn.On = isExpanded[indexPath.Row];

    return cell;
}

At last, we can override the GetHeightForRow event. Set a large or small value depending on the item in the isExpanded:

public override nfloat GetHeightForRow(UITableView tableView, NSIndexPath indexPath)
{
    if (isExpanded[indexPath.Row])
    {
        return 80;
    }
    return 40;
}

Here is some part of my cell for you referring to:

//When switch's value changed, this event will be called
public delegate void RefreshHanle(MyListViewCell cell, bool isOn);
public event RefreshHanle RefreshEvent;
switchBtn.AddTarget((sender, args) =>
{
    UISwitch mySwitch = sender as UISwitch;
    RefreshEvent(this, mySwitch.On);
}, UIControlEvent.ValueChanged);