使用ViewCellRenderer在iOS上的Xamarin表单中ViewCell的自动高度

Question

For performance reasons I decided to write a custom ViewCell for my ListView in Xamarin Forms. For this ViewCell I've extended the ViewCellRenderer for iOS. In the GetCell-Method I create a new instance of an extended UITableViewCell which creates some labels and images and arranges them by some constraints on the anchors.

The ListView in Xamarin Forms has HasUnevenRows="True", but the rows are all cut-off at 44px. How can I get automatic height to the rows by the created content from the custom UITableViewCell?

Answer 1

You should override LayoutSubviews . You should set renderer.NativeView.Frame to proper values.

Answer 2

Cause:

Actually, The auto height with HasUnevenRows=true works fine on iOS if not using a custom renderer.

If using a custom renderer, then it is up to the renderer to set the height of the cell , but in reality you have to do it in the GetHeightForRow override of the UITableViewSource .

This means you have to calculate the row height in UITableViewSource that you make that sets the height for a row in the GetHeightForRows override if you want to use custom viewcell render in the listView with uneven rows.

Solution:

Basically you have to make a custom ListView renderer . Then you have to get the UITableView's Source property (Control.Source in the list view renderer) and pass that to a new instance of a subclass of UITableVIewSource that you create, and then override all of the UITableViewSource methods so you can call into the original source methods when you don't want to change anything, but for the GetRowForHeight method, you would return the height you want for that row. EG:

[assembly: ExportRenderer(typeof(ListView), typeof(MyLVRenderer))]
public class MyLVRenderer : ListViewRenderer
    {
        //UITableViewSource originalSource;

        protected override void OnElementChanged(ElementChangedEventArgs<ListView> e)
        {
            base.OnElementChanged(e);

            UITableViewSource originalSource = (UIKit.UITableViewSource)Control.Source;
            Control.Source = new MyLVSource(originalSource);

        }
    }

    public class MyLVSource : UITableViewSource
    {
        UITableViewSource originalSource;

        public MyLVSource(UITableViewSource origSource)
        {
            originalSource = origSource;
        }

        public override nint RowsInSection(UITableView tableview, nint section)
        {
            return originalSource.RowsInSection(tableview, section);
        }

        public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
        {
            return originalSource.GetCell(tableView, indexPath);
        }

        public override nfloat GetHeightForFooter(UITableView tableView, nint section)
        {
            return originalSource.GetHeightForFooter(tableView, section);
        }

        public override nfloat GetHeightForRow(UITableView tableView, NSIndexPath indexPath)
        {
            nfloat origHeight = originalSource.GetHeightForRow(tableView, indexPath);

            // calculate your own row height here
            return origHeight + (indexPath.Row +1) * 10;
        }                
    }

This is a example of increasing the row height by ten for every row. You have to calculate your own row height by yourself. I can share you the demo if you need.

Refer: viewcell