Image Switcher View | Android Developer Tutorial

Now we will explore ImageSwitcher View. It is a view useful to switch smoothly between two images and thus provides ways of transitioning from one to another through appropriate animations.

We will implement the same concept of showing a gallery of images that scrolls at the top of the android screen landscape and upon selection of one image, it gets displayed as a larger image in the lower part through the use of an ImageSwitcher. This is what I had done earlier in the GalleryView tutorial but now instead of showing the selected picture through an ImageView, I will show it using a ImageSwitcher. Though the output may seem very similar, lot of other methods are available on the ImageSwitcher that can be used, if required.

Here is how the output would look (NOTE that I have not used the default gallery background provided by Android in the Gallery images)

So, to begin with, first we need to declare the layout xml to have a gallery and the ImageSwitcher:

<Gallery

      android:id="@+id/Gallery01"

      android:layout_width="fill_parent"

      android:layout_height="wrap_content"></Gallery>

<ImageSwitcher

      android:id="@+id/ImageSwitcher01"

      android:layout_width="fill_parent"

      android:layout_height="fill_parent">

</ImageSwitcher>

The next thing that we need to do is create a class that not only extends Activity but also implements ViewFactory. The ViewFactory is a Interface that creates views that need to be shown in the ImageSwitcher. So it has one method makeView() which we need to implement. It is here that we can set the attributes of the ImageView that would be shown within the ImageSwitcher -  like its background, it scale, its layout parameters etc. – typically those attributes that we would have otherwise statically set through a layout xml.

Here is the class declaration and the method makeView():

public class ImageSwitcherView extends Activity implements ViewFactory {

and

      @Override

      public View makeView() {

            ImageView iView = new ImageView(this);

            iView.setScaleType(ImageView.ScaleType.FIT_CENTER);

            iView.setLayoutParams(new

                        ImageSwitcher.LayoutParams(

                                    LayoutParams.FILL_PARENT,LayoutParams.FILL_PARENT));

            iView.setBackgroundColor(0xFF000000);

            return iView;

      }

This alone is the real difference from the Gallery example.

Other smaller things we need to do is get a handle to the ImageSwitcher in the onCreate() method:

            iSwitcher = (ImageSwitcher) findViewById(R.id.ImageSwitcher01);

            iSwitcher.setFactory(this);

            iSwitcher.setInAnimation(AnimationUtils.loadAnimation(this,

                        android.R.anim.fade_in));

            iSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this,

                        android.R.anim.fade_out));

Here we also set the animation on how the image should fly in and fly out of the area. Then, we get a handle to the gallery and set an ImageAdapter to it. The ImageAdpater is as described in my Gallery Example. If you have not seen that, please go through that and then try this example, as I would not want to repeat myself here.

Now on the click of a gallery image, we would want to pass the selected image to the ImageSwitcher and this is what we do here:

            gallery.setOnItemClickListener(new OnItemClickListener() {

                  @Override

                  public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {

                        iSwitcher.setImageResource(pics[arg2]);

                  }

            });

      }

This way we are done. You may download the complete code here.

Gallery View | Android Developer Tutorial

Continuing on the Views, I have taken up the Gallery View that helps in showing Images as in a gallery. As per the android documentation, this is the definition: “A Gallery is a View commonly used to display items in a horizontally scrolling list that locks the current selection at the center.”


For this the layout xml in this case, the main.xml will have a ‘Gallery’ element as shown below:

<Gallery
    android:id="@+id/Gallery01"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"></Gallery>
<ImageView android:id="@+id/ImageView01"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"></ImageView>

It also has an ImageView element which is used to show the selected Image in a larger ImageView. Here is how it would look when executed.

Now, I create a GalleryView Activity. To view a set of images of Antartica, I have created small sized images of antartica and stored them in the res/drawable-ldpi folder starting form antartica1.png to antartica10.png.

I create an array of these resources/images in my activity with the following code:

Integer[] pics = {
R.drawable.antartica1,
R.drawable.antartica2,
R.drawable.antartica3,
R.drawable.antartica4,
R.drawable.antartica5,
R.drawable.antartica6,
R.drawable.antartica7,
R.drawable.antartica8,
R.drawable.antartica9,
R.drawable.antartica10
};

As we have seen with all the other views so far, we need to have an adapter that associates the view with the data. Here the view is Gallery and the data is the above mentioned 10 images. An Adapter plays the role of linking the two as shown below:

Gallery ga = (Gallery)findViewById(R.id.Gallery01);
ga.setAdapter(new ImageAdapter(this));

However, we do not have a readymade implementation of the ImageAdapter. We have to create our own implementation of the same by extending the BaseAdapter class. This is the core of the code in this example. The moment we extend the BaseAdapter, we have to override 4 methods. They are getCount(), getItem(), getItemId() and getView().

Before we go to each of them, let us see the constructor of the ImageAdpater:

public class ImageAdapter extends BaseAdapter {


private Context ctx;
int imageBackground;


public ImageAdapter(Context c) {
    ctx = c;
    TypedArray ta = obtainStyledAttributes(R.styleable.Gallery1);
    imageBackground = ta.getResourceId(R.styleable.Gallery1_android_galleryItemBackground, 1);
    ta.recycle();
}
…
}

It takes the context that is passed to the constructor. We need to examine this code a little. First, we can define our own resources or attributes in an XML file. Those attributes can be retrieved through the method obtainStyledAttributes. This is a method on the Context object. The returned value needs to be stored in a TypedArray object. A TypedArray is nothing but a container for an array of values that are returned by obtainStyledAttributes.

So, in my example, I have created an xml file by name attributes.xml in the res/values folder with the following content:

<resources>
     <declare-styleable name="Gallery1">
    <attr name="android:galleryItemBackground"/>
     </declare-styleable>
</resources>

Here Gallery1 is a custom name for a style defined by us. In this style, we are trying to say what should be the background of our images. For that we are using a pre-defined backgournd in R.attr class as galleryItemBackground.

So, this is accessed in the ImageAdapter contructor through the line

ta.getResourceId(R.styleable.Gallery1_android_galleryItemBackground, 1);
ta.recycle();

The number 1 is to say that it is the first element in the attributes.xml file under the styelable Gallery1.

The rest of the over ridden methods are simple:

@Override
public int getCount() {
    return pics.length;
}


@Override
public Object getItem(int arg0) {
    return arg0;
}

@Override
public long getItemId(int arg0) {
    return arg0;
}


@Override
public View getView(int arg0, View arg1, ViewGroup arg2) {
    ImageView iv = new ImageView(ctx);
    iv.setImageResource(pics[arg0]);
    iv.setScaleType(ImageView.ScaleType.FIT_XY);
    iv.setLayoutParams(new Gallery.LayoutParams(150,120));
    iv.setBackgroundResource(imageBackground);
    return iv;
}

The getView actually returns a View object when called. Here I have overridden it to return a ImageView object with the selected image inside it alosn with some scale, layout paramaters and the image background set.

Finally in the onCreate() method of the activity I have captured the onClick event on a Gallery item and within that I have toasted a message as well as displayed the image in a bigger manner below the gallery:

ga.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
    Toast.makeText(getBaseContext(), "You have selected picture " + (arg2+1) + " of Antartica",
        Toast.LENGTH_SHORT).show();
    imageView.setImageResource(pics[arg2]);
}
});

That is it. You may download the complete code from here.

Spinner View | Android Beginner Dev Tutorial

This is again another very simple tutorial on using a Spinner View provided by Android SDK. A spinner is supposed to be a view that displays one child at a time (Whatever that means).


This example is very similar to the previous one on AutoCompleteTextView.

Jumping right into the code, here is the layout xml file:

<Spinner
android:id="@+id/Spinner01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawSelectorOnTop = "true"></Spinner>


Nothing special. It just consists of one element.

Now in the main activity, I create an array of android books:

String[] androidBooks =
{
"Hello, Android - Ed Burnette",
"Professional Android 2 App Dev - Reto Meier",
"Unlocking Android - Frank Ableson",
"Android App Development - Blake Meike",
"Pro Android 2 - Dave MacLean",
"Beginning Android 2 - Mark Murphy",
"Android Programming Tutorials - Mark Murphy",
"Android Wireless App Development - Lauren Darcey",
"Pro Android Games - Vladimir Silva",
};

Then in the onCreate() method, I create an ArrayAdapter that I can pass to this Spinner as the data Source.

ArrayAdapter<String> adapter =
        new ArrayAdapter<String> (this,
        android.R.layout.simple_spinner_item,androidBooks);

Then, I get a handle to the Spinner, and set the ArrayAdapter to it

sp = (Spinner)findViewById(R.id.Spinner01);
sp.setAdapter(adapter);

Now, on selecting one of the items in the spinner, I want to be able to toast a message on the book that was selected. It is done as follows:

sp.setOnItemSelectedListener(new OnItemSelectedListener() {
    @Override
    public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
        int item = sp.getSelectedItemPosition();
        Toast.makeText(getBaseContext(),
            "You have selected the book: " + androidBooks[item],
            Toast.LENGTH_SHORT).show();
    }


    @Override
    public void onNothingSelected(AdapterView<?> arg0) {
    }
});

That is it. Now execute and see it work. Here is how it would look:

The example code can be downloaded here.