How to use List<Hashtable> from c#

Question

How to store and retrieve values from List in C#? I can store values like this

List<Hashtable> mList=new List<Hashtable>();
Hashtable ht = new Hashtable();
ht.Add(1, "One");
ht.Add(2, "Two");
ht.Add(3, "Three");
ht.Add(4, "Four");
mList.Add(ht);

How to set these values to base adapter textview in C#?

Answer 1

How to set these values to base adapter textview in C#?

I assume that your base adapter means the BaseAdapter for a ListView, then you can create a adapter inherit from BaseAdapter for example like this:

public class MainAdapter : BaseAdapter<Hashtable>
{
    private List<Hashtable> items;
    private Activity context;

    public MainAdapter(Activity context, List<Hashtable> items) : base()
    {
        this.context = context;
        this.items = items;
    }

    public override Hashtable this[int position]
    {
        get
        {
            return items[position];
        }
    }

    public override int Count
    {
        get
        {
            return items.Count;
        }
    }

    public override long GetItemId(int position)
    {
        return position;
    }

    public override View GetView(int position, View convertView, ViewGroup parent)
    {
        View view = convertView;
        if (view == null)
            view = context.LayoutInflater.Inflate(Android.Resource.Layout.SimpleListItem1, null);
        view.FindViewById<TextView>(Android.Resource.Id.Text1).Text = items[position].ToString();
        return view;
    }
}

and use the List<HashTable> for your adapter like this:

public class MainActivity : ListActivity
{
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        // Set our view from the "main" layout resource
        //SetContentView(Resource.Layout.Main);

        List<Hashtable> mList = new List<Hashtable>();
        Hashtable ht = new Hashtable();
        ht.Put(1, "One");
        ht.Put(2, "Two");
        ht.Put(3, "Three");
        ht.Put(4, "Four");
        mList.Add(ht);

        ListAdapter = new MainAdapter(this, mList);
    }
}

But I doubt this is really what you need. You have only one item in List<> and this item has one Hashtable which contains four key-pair value. Is it possible that you need a key-pair value to be shown on each item of ListView instead of showing four key-pair values in one item?

I do agree with @Henk Holterman, it is very strange to put an old-style hashtable in a List<>, if you want to use List<> to store multiple string values with key, you can simply code like this:

List<string> mList = new List<string>();
mList.Add("One");
mList.Add("Two");
mList.Add("Three");
mList.Add("Four");

List<> itself allocates a index for each item, for example, if you want to find the index of string item "Three", you can code like this:

var index = mList.IndexOf("Three");

Since the first item in List<> will match the index of 0, here the index of item "Three" will be 2.

Of course I'm not saying it is not allowed to store a Hashtable into a List<>, but usually when we want to define a Key for each item, one method is to create a class model, for example:

public class MyListModel
{
    public int Key { get; set; }
    public string Content { get; set; }
}

And now you can create a List<> for this model:

List<MyListModel> mList = new List<MyListModel>();
for (int i = 1; i <= 10; i++)
{
    mList.Add(new MyListModel { Key = i, Content = "item " + i });
}

The advantage to use a data model for ListView is that if your each ListView item has for example more than one TextView, each is for displaying different information, then you can simply add those properties in this class model.

For more information of building a ListView in Xamarin.Android, you can refer to ListViews and Adapters.