Xamarin.Android: Changing a specific value in a list during runtime - list

Question

I have a simple Xamarin.Android-App.
On the Activity of this app, there is a list displayed. Please see following MyActivity.axml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android ="http://schemas.android.com/apk/res/android"
android:orientation ="vertical"
android:layout_width ="match_parent"
android:layout_height="match_parent">
<Button
android:layout_width ="match_parent"
android:layout_height="wrap_content"
android:text ="Click Me"
android:layout_marginTop ="20dp"
android:layout_marginLeft ="25dp"
android:layout_marginRight ="25dp"
android:id="#+id/button" />
<Space
android:layout_width="match_parent"
android:layout_height="25dp"
android:id="#+id/space" />
<ListView
android:minWidth="25px"
android:minHeight="25px"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/list" />
</LinearLayout>
One row of this list contains simply two entries, please see ListRow.axml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView
android:id="#+id/name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft ="5dp"
android:layout_marginTop ="10dp"
android:layout_marginBottom="10dp"
android:layout_marginRight ="5dp" />
<TextView
android:id="#+id/value"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft ="5dp"
android:layout_marginTop ="10dp"
android:layout_marginBottom="10dp"
android:layout_marginRight ="5dp" />
</RelativeLayout>
So the code-behind of that activity looks like the following:
public class MyActivity : Activity
{
List<Entry> List = null;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
SetContentView(Resource.Layout.MyActivity);
List = PopulateList();
var lv = FindViewById<ListView>(Resource.Id.list);
var adapter = new ListAdapter(this, Resource.Layout.List, List);
lv.Adapter = adapter;
FindViewById<Button>(Resource.Id.button).Click += OnButtonClick;
}
}
For the sake of completeness, here is the code for my ListAdapter.cs-class:
class ListAdapter : ArrayAdapter
{
List<Entry> List;
public ListAdapter(Context Context, int ListId, List<Entry> List) : base(Context, ListId, List)
{
this.List = List;
}
public override int Count
{
get { return List.Count; }
}
public override View GetView(int position, View convertView, ViewGroup parent)
{
View v = convertView;
if (v == null)
{
LayoutInflater inflater = (LayoutInflater)Context.GetSystemService(Context.LayoutInflaterService);
v = inflater.Inflate(Resource.Layout.List, parent, false);
}
v.FindViewById<TextView>(Resource.Id.name).Text = List[position].Name;
v.FindViewById<TextView>(Resource.Id.value).Text = "Original Value";
return v;
}
}
So my question now is the following: Assuming that there is more than one item within that List. On click of the button, I want to change one specific text within that list. Let's say of the second entry in the list the (Resource.Id.value).Text (which now says "Original Value") to "Changed Value" or something like that. But only of the second one. All the other items should stay the same.
Please see following example of output aimed, maybe it's easier to understand what I am trying to do:
Name Value
- - - - - - - - - - - - - - - -
No.1 Original Value
No.2 Original Value
No.3 Original Value
[Button Click]
Name Value
- - - - - - - - - - - - - - - -
No.1 Original Value
No.2 Changed Value
No.3 Original Value
Can anyone maybe help me / tell me how to do this? What does my private void OnButtonClick(object sender, EventArgs e)-method have to look like? How can I access a single entry in that list?
Thanks in advance for all answers and best regards

Answer 1

you could add a method in adapter to notifyDataSetChanged(); :
class ListAdapter : ArrayAdapter
{
List<Entry> List;
private int ItemPositionToChange = -1;
public ListAdapter(Context Context, int ListId, List<Entry> List) :
base(Context, ListId, List)
{
this.List = List;
}
//this method to let adapter notify
public void ChangeItemValue(int position)
{
ItemPositionToChange = position;
NotifyDataSetChanged();
}
public override int Count
{
get { return List.Count; }
}
public override View GetView(int position, View convertView, ViewGroup parent)
{
View v = convertView;
if (v == null)
{
LayoutInflater inflater =
(LayoutInflater)Context.GetSystemService(Context.LayoutInflaterService);
v = inflater.Inflate(Resource.Layout.List, parent, false);
}
v.FindViewById<TextView>(Resource.Id.name).Text = List[position].Name;
//change the item value according to your needs
if(position == ItemPositionToChange ){
v.FindViewById<TextView>(Resource.Id.value).Text = "Changed Value";
}else{
v.FindViewById<TextView>(Resource.Id.value).Text = "Original Value";
}
return v;
}
}
then in your button click listener :
void OnButtonClick(object sender, EventArgs e)
{
//positionToChange is which item you want to change
adapter.ChangeItemValue(positionToChange);
}

Answer 2

I'm not too familiar with the Entry class, but it seems to have a Text property.
Assuming you know the index of the string (myIndex below):
private void OnButtonClick(object sender, EventArgs e) {
List[myIndex].Text = "Changed Value";
adapter.notifyDataSetChanged();
}