xamarin - 添加注释 MapView - Xamarin

Question

我正在尝试使用我的表格视图添加注释。添加了初始注释，但每当我单击我的表格视图以调用其他位置时。它给了我一个错误（nullexception）。有没有人可以帮帮我？

using System;
using System.Drawing;
using MonoTouch.Foundation;
using MonoTouch.UIKit;
using MonoTouch.MapKit;
using MonoTouch.CoreLocation;

namespace FieldMobileApp
{
    public partial class MainRightViewController : UIViewController
    {
        UITableView table;
        MKMapView mapView;
        BasicMapAnnotation annotation = new BasicMapAnnotation (new CLLocationCoordinate2D (48.857, 2.351), "Paris", "City of Light");
        public MainRightViewController () : base ("MainRightViewController", null)
        {
            this.Title ="Right View Controller";
        }

        public override void DidReceiveMemoryWarning ()
        {
            // Releases the view if it doesn't have a superview.
            base.DidReceiveMemoryWarning ();

            // Release any cached data, images, etc that aren't in use.
        }
        string[] tableItems = new string[] { "Harris", "Lubbock", "Galveston", "College Station", "Sugar Land", "Tulsa","Meyerland","Pearland","Linkwood","Valley Hills","Simav","Bursa"};
        double[] lat = new double[] { 42, 36, 25, 18, 19, 58, 62, 10, 5, 6, 44, 55, 62 };
        double [] lng=  new double[] { -42, -36, -25, -18, -19, -58, -62, -10, -5, -6, -44, -55, -62 };

        public override void ViewDidLoad ()
        {
            base.ViewDidLoad ();
            table = new UITableView (new RectangleF(80,80,250,500));
            table.AutoresizingMask = UIViewAutoresizing.All;
            table.Source = new TableSource (tableItems);
            Add(table);

            mapView = new MKMapView(new RectangleF (538,78,408,639));   
            mapView.AutoresizingMask = UIViewAutoresizing.FlexibleDimensions;
            View.AddSubview(mapView);

            // create our location and zoom for los angeles
            var coords = new CLLocationCoordinate2D(48.857, 2.351); 

            // add a basic annotation
            //var annotation = new BasicMapAnnotation (new CLLocationCoordinate2D (48.857, 2.351), "Paris", "City of Light");
            mapView.AddAnnotation (annotation);

            // Perform any additional setup after loading the view, typically from a nib.
        }




        public void ciz(int i)
        {

            var annotation = new BasicMapAnnotation (new CLLocationCoordinate2D (lat[i], lng[i]), "Tayfun Place", "City of Knowledge");

            Console.WriteLine ("{0},{1}", lat [i], lng [i]);
                    // following line gives me an error, null exception!
            mapView.AddAnnotation (annotation);

        }


        public class TableSource : UITableViewSource {
            protected string[] tableItems;
            protected string cellIdentifier = "TableCell";
            public MainRightViewController parentController= new MainRightViewController();

            public TableSource (string[] items)
            {
                tableItems = items;
            }

            /// <summary>
            /// Called by the TableView to determine how many cells to create for that particular section.
            /// </summary>
            public override int RowsInSection (UITableView tableview, int section)
            {
                return tableItems.Length;
            }

            /// <summary>
            /// Called when a row is touched
            /// </summary>

            public override void RowSelected (UITableView tableView, NSIndexPath indexPath)
            {
                new UIAlertView("Row Selected"
                                , tableItems[indexPath.Row], null, "OK", null).Show();
                tableView.DeselectRow (indexPath, true);
            }

            /// <summary>
            /// Called by the TableView to get the actual UITableViewCell to render for the particular row
            /// </summary>
            public override UITableViewCell GetCell (UITableView tableView, MonoTouch.Foundation.NSIndexPath indexPath)
            {
                // request a recycled cell to save memory
                UITableViewCell cell = tableView.DequeueReusableCell (cellIdentifier);
                // if there are no cells to reuse, create a new one
                if (cell == null)
                    cell = new UITableViewCell (UITableViewCellStyle.Default, cellIdentifier);

                cell.TextLabel.Text = tableItems[indexPath.Row];

                return cell;
            }
        }

        protected class BasicMapAnnotation : MKAnnotation
        {
            /// <summary>
            /// The location of the annotation
            /// </summary>
            public override CLLocationCoordinate2D Coordinate { get; set; }
            protected string title;
            protected string subtitle;

            /// <summary>
            /// The title text
            /// </summary>
            public override string Title
            { get { return title; } }


            /// <summary>
            /// The subtitle text
            /// </summary>
            public override string Subtitle
            { get { return subtitle; } }

            public BasicMapAnnotation (CLLocationCoordinate2D coordinate, string title, string subTitle)
                : base()
            {
                this.Coordinate = coordinate;
                this.title = title;
                this.subtitle = subTitle;
            }
        }

    }
}

Answer 1

您不应该在 TableSource 实例中创建新的 MainRightViewController ，而是将其传递给您从中调用它的实例。

public partial class MainRightViewController : UIViewController
{
    (...)

    public override void ViewDidLoad ()
    {
        (...)

        table.Source = new TableSource (tableItems, this);

在你的 UITableViewSource 中：

public class TableSource : UITableViewSource {

        public MainRightViewController parentController;

        public TableSource (string[] items, MainRightViewController parentController)
        {
            tableItems = items;
            this.parentController = parentController
        }

我希望这可以帮助您继续前进。