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Gallery

Gallery is a layout widget used to display items in a horizontally scrolling list and positions the current selection at the center of the view.

In this tutorial, you'll create a gallery of photos and then display a toast message each time a gallery item is selected.

After the Main.axml layout is set for the content view, the Gallery is captured from the layout with FindViewById(int). The Adapter property is then used to set a custom adapter (ImageAdapter) as the source for all items to be displayed in the dallery. The ImageAdapter is created in the next step.

To do something when an item in the gallery is clicked, an anonymous delegate is subscribed to the ItemClick event. It shows a Toast that displays the index position (zero-based) of the selected item (in a real world scenario, the position could be used to get the full sized image for some other task).

First, there are a few member variables, including an array of IDs that reference the images saved in the drawable resources directory (Resources\Drawable\).

Next is the class constructor, where the Context for an ImageAdapter instance is defined and saved to a local field. Next, this implements some required methods inherited from BaseAdapter. The constructor and the Count property are self-explanatory. Normally, GetItem(int) should return the actual object at the specified position in the adapter, but it's ignored for this example. Likewise, GetItemId(int) should return the row id of the item, but it's not needed here.

The method does the work to apply an image to an ImageView that will be embedded in the Gallery. In this method, the member Context is used to create a new ImageView. The ImageView is prepared by applying an image from the local array of drawable resources, setting the Gallery.LayoutParams height and width for the image, setting the scale to fit the ImageView dimensions, and then finally setting the background to use the styleable attribute acquired in the constructor.

See ImageView.ScaleType for other image scaling options.

Walkthrough

  1. Start a new project named HelloGallery.
  2. Find some photos you'd like to use, or download these sample images. Add the image files to the project's Resources/Drawable/ directory. In the Properties window, set the Build Action for each to AndroidResource.
  3. Open the Resources/Layout/Main.axml file and insert the following:
    <?xml version="1.0" encoding="utf-8"?>
    <Gallery xmlns:android="http://schemas.android.com/apk/res/android" 
        android:id="@+id/gallery"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
    />
    
  4. Open Activity1.cs and insert the following code for the OnCreate() method:
    protected override void OnCreate (Bundle bundle)
    {
        base.OnCreate (bundle);
    
        // Set our view from the "main" layout resource
        SetContentView (Resource.Layout.Main);
    
        Gallery gallery = (Gallery) FindViewById<Gallery>(Resource.Id.gallery);
    
        gallery.Adapter = new ImageAdapter (this);
    
        gallery.ItemClick += delegate (object sender, Android.Widget.AdapterView.ItemClickEventArgs args) {
            Toast.MakeText (this, args.Position.ToString (), ToastLength.Short).Show ();
        };
    }
    
  5. Create a new class called ImageAdapter that subclasses BaseAdapter:
    public class ImageAdapter : BaseAdapter
    {
         Context context;
    
         public ImageAdapter (Context c)
         {
             context = c;
         }
    
        public override int Count { get { return thumbIds.Length; } }
    
        public override Java.Lang.Object GetItem (int position)
        {
              return null;
        }
    
        public override long GetItemId (int position)
        {
              return 0;
        }
    
        // create a new ImageView for each item referenced by the Adapter
        public override View GetView (int position, View convertView, ViewGroup parent)
        {
              ImageView i = new ImageView (context);
    
              i.SetImageResource (thumbIds[position]);
              i.LayoutParameters = new Gallery.LayoutParams (150, 100);
              i.SetScaleType (ImageView.ScaleType.FitXy);
    
              return i;
        }
    
        // references to our images
        int[] thumbIds = {
                Resource.Drawable.sample_1,
                Resource.Drawable.sample_2,
                Resource.Drawable.sample_3,
                Resource.Drawable.sample_4,
                Resource.Drawable.sample_5,
                Resource.Drawable.sample_6,
                Resource.Drawable.sample_7
         };
    }
    
  6. Run the application. It should look like the screenshot below:

References

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License. This tutorial is based on the Android Gallery tutorial.