Programmatically set the background color of a list view item

问题

In my app, I have to automatically set the background color of a ListView item, based on the string content of that list view item.

Currently, the app is using the below code:

    private void UpdateListView(string itemFromList, ListView listView)
    {
        int itemListPosition = listViewAdapter.GetPosition(itemFromList);
        listView.SetItemChecked(itemListPosition, true);

        View child = listView.GetChildAt(itemListPosition);

        if (child != null)
        {
            for (int i = 0; i < listViewAdapter.Count; i++)
            {
                View otherChild = listView.GetChildAt(i);

                if (otherChild != null)
                {
                    otherChild.SetBackgroundColor(defaultColor);
                }
            }

            child.SetBackgroundColor(Color.Green);
        }
    }

where listViewAdapter is a global variable in the MainActivity class defined as below into the onCreate method:

listViewAdapter= new ArrayAdapter<String>(this, Android.Resource.Layout.SimpleListItem1, settingItems);
listView.Adapter = listViewAdapter;

and settingItems is just a global variable defined as a list of strings.

The above code was working fine, so the background color of a given list view item was changing to green and the rest of the list view items to the default color, until the list view added a vertical scroll to it.

Now after the list view got more items and a vertical scroll all the time the

View child = listView.GetChildAt(itemListPosition);

child object from the above call is null. Consequently, I can't access anymore the items from the list view based on their position. Do you know how can I work around this?

回答1:

I wrote a demo in GetView method, set the item background color, you could refer to it.

This is GIF of demo.

You could change code in the GetView method of listview adapter. I do not know which items you want to change in listview, so I set the position in 1,3,5. you could change it by yourself.

MyAdapter.cs

   class MyAdapter : BaseAdapter<ColorDemo>
{
    Activity context;
    List<ColorDemo> colors { get; set; }
    public MyAdapter(Activity context , List<ColorDemo> colors)
    {
        this.context = context;
        this.colors = colors;

    }

    public override ColorDemo this[int position] {
        get
        {
            return colors[position];
        }
    }

    public override int Count => colors.Count;



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

    public override View GetView(int position, View convertView, ViewGroup parent)
    {
        View newView = convertView;
        if (newView == null)
            newView = context.LayoutInflater.Inflate(Resource.Layout.ItemView, null);
        newView.FindViewById<TextView>(Resource.Id.item_tv).Text = colors[position].ColorName;
        if (position==1|| position == 3|| position == 5)
        {
            newView.FindViewById<TextView>(Resource.Id.item_tv).SetBackgroundColor( Color.Blue);

        }
        else
        {
            newView.FindViewById<TextView>(Resource.Id.item_tv).SetBackgroundColor(Color.Green);

        }

       return newView;

    }
}

The following is activity_main.axml and ItemView.axml, you could customize items in the listview by ItemView

activity_main.axml

 <?xml version="1.0" encoding="utf-8"?>
 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent" 
        android:id="@+id/lv_color"
     />
  </RelativeLayout>

ItemView.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">
  <TextView 
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="this text"
    android:textSize="50dp"
    android:id="@+id/item_tv"
    android:background="@android:color/holo_red_dark"
    />
</LinearLayout>

The following code is related to the MainActivity.cs

MainActivity.cs

    [Activity(Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
public class MainActivity : AppCompatActivity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.activity_main);
        ListView lv_color = FindViewById<ListView>(Resource.Id.lv_color);
       // lv_color.SetItemChecked(2,true);
        List<ColorDemo> colors = new List<ColorDemo>();
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));

        MyAdapter myAdapter = new MyAdapter(this,colors);
        lv_color.Adapter=myAdapter;
    }
}

来源：https://stackoverflow.com/questions/54011699/programmatically-set-the-background-color-of-a-list-view-item