Understanding User Interface in Android – Part 3: More Views

In the previous article, you saw the various basic views such as the TextView, EditText, Button, and how you can use them in your Android applications. In this article, we shall continue our exploration of another three categories of views – Picker views, List views, and Display views. The views discussed include:

  • TimePicker view
  • DatePicker view
  • ListView view
  • Spinner view
  • Gallery view
  • ImageView
  • ImageSwitcher view
  • GridView view

Note: for all the examples in this article, you shall use the project created in the previous article.

Picker Views

Selecting date and time is one of the very common tasks you need to perform in a mobile application. Android supports this functionality through the TimePicker and DatePicker views.

TimePicker View

The TimePicker view allows users to select a time of the day, in either 24 hour mode or AM/PM mode.
Add a new file to the res/layout folder and name it as datetimepicker.xml and populate it with the following element:

Add a new class to the src/net.learn2develop.AndroidViews folder and name it as DateTimePickerExample.java. Populate it as follows:

Modify the AndroidManifest.xml file to register the new activity:

Modify the ViewsActivity.java file to start the DateTimePickerExample activity:

Press F11 to debug the application on the Android emulator. Figure 1 shows the TimePicker view in action. You can use the numeric keypad on the device to change the hour and minute and click on the AM button to toggle between AM and PM.


Figure 1: The TimePicker view in action

Displaying the TimePicker View in a Dialog Window

You can also display the TimePicker view in a dialog. Modify the DateTimePickerExample.java file as shown below:

The above program displays the TimePickerDialog when the activity is created. When the time is set, the selected time is displayed using the Toast class. Figure 2 shows the TimePickerDialog in action.


Figure 2: The TimePickerDialog in action

DatePicker View

Like the TimePicker view, the DatePicker view allows users to select a date. Modify the datetimepicker.xml file as follows:

Remove the following statement added in the previous section:

Press F11 to debug the application on the Android emulator. Figure 3 shows the DatePicker view in action. Besides touching the “+” and “-“ buttons, you can also use the numeric keypad on the device to change the month, day, and year.


Figure 3: The DatePicker view in action

Displaying the DatePicker View in a Dialog Window

You can also display the DatePicker view in a dialog. Modify the DateTimePickerExample.java file as shown below:

The above program displays the DatePickerDialog when the activity is created. When the date is set, the set date is displayed using the Toast class. Figure 4 shows the DatePickerDialog in action.


Figure 4: The DatePickerDialog in action

List Views

The ListView and Spinner views are useful for displaying long lists of items.

ListView View

The ListView view displays a list of items in a vertically scrolling list. To see how the ListView view works, add a new file to the res/layout folder and name it as listview.xml and populate it with the following element:

Add a new class to the src/net.learn2develop.AndroidViews folder and name it as ListViewExample.java. Populate it as follows:

Notice that the ListViewExample class extends the ListActivity class.

Modify the AndroidManifest.xml file to register the new activity:

Modify the ViewsActivity.java file as follows to start the ListViewExample activity:

Press F11 to debug the application on the Android emulator. Figure 5 shows the ListView view in action. When an item is selected, a message will be displayed.


Figure 5: The ListView view in action

Spinner View

The Spinner view displays an item at a time from a list and lets the users choose among them.
Add a new file to the res/layout folder and name it as spinner.xml and populate it with the following element:

Modify the ViewsActivity.java file to start the SpinnerExample activity:

Figure 7 shows the new appearance of the Spinner view.


Figure 7: The Spinner view

Display Views

So far all the views you have seen are used to display text information. For displaying images, you can use the ImageView, Gallery and ImageSwitcher views.

Gallery and ImageView Views

The Gallery is a view that shows items (such as images) in a center-locked, horizontal scrolling list. Figure 8 shows the Gallery view used in the Android Market.


Figure 8: The Gallery view used in the Android Market

To see how the Gallery view works, add a new file to the res/layout folder and name it as displayview.xml and populate it with the following elements:

The Gallery1 style is used to apply to images displayed in the Gallery view so that the each image has a border around it (see Figure 9).


Figure 9: Gallery view, with borders on images

Add a few images to the res/drawable folder (see Figure 10).


Figure 10: Adding images

Add a new class to the src/net.learn2develop.AndroidViews folder and name it as DisplayViewsExample.java. Populate it as follows:

Modify the ViewsActivity.java file as follows to start the DisplayViewsExample activity:

When an image is selected, it will now be displayed in the ImageView view below (see Figure 12).


Figure 12: Selected image displayed in ImageView view

ImageSwitcher View

You saw in the previous section on how to use the Gallery view together with an ImageView view to display a series of thumbnail images so that when one is selected, the selected image is displayed in the ImageView view. Because this is such a common UI task, Android provides the ImageSwitcher view, which is functionally similar to what you have achieved in the previous section.

Modify the displayview.xml file as follows by adding the ImageSwitcher element:

In the DisplayViewsExample.java file, code the following:


package net.learn2develop.AndroidViews;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;

public class DisplayViewsExample extends Activity
{
//---the images to display---
Integer[] imageIDs = {
R.drawable.pic1,
R.drawable.pic2,
R.drawable.pic3,
R.drawable.pic4,
R.drawable.pic5,
R.drawable.pic6,
R.drawable.pic7
};

@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.displayview);

GridView gridView = (GridView) findViewById(R.id.gridview);
gridView.setAdapter(new ImageAdapter(this));

gridView.setOnItemClickListener(new OnItemClickListener()
{
public void onItemClick(AdapterView parent,
View v, int position, long id)
{
Toast.makeText(getBaseContext(),
"pic" + (position + 1) + " selected",
Toast.LENGTH_SHORT).show();
}
});
}

public class ImageAdapter extends BaseAdapter
{
private Context context;

public ImageAdapter(Context c)
{
context = c;
}

//---returns the number of images---
public int getCount() {
return imageIDs.length;
}

//---returns the ID of an item---
public Object getItem(int position) {
return position;
}

public long getItemId(int position) {
return position;
}

//---returns an ImageView view---
public View getView(int position, View convertView, ViewGroup parent)
{
ImageView imageView;
if (convertView == null) {
imageView = new ImageView(context);
imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(5, 5, 5, 5);
} else {
imageView = (ImageView) convertView;
}
imageView.setImageResource(imageIDs[position]);
return imageView;
}
}
}

Observe that the code is very similar to the Gallery view example – you create the ImageAdapter class (which extends the BaseAdapter class) so that it can bind to the GridView view with a series of ImageView views. The ImageView view is used to display images. When an image is selected, the position of the image is displayed using the Toast class.

Press F11 to debug the application. Figure 14 shows the GridView view in action.


Figure 14: The Gridview in action

Summary

In this article, you have seen the various views in the Picker, List and Display views category. Hopefully, you have a better understanding of them and are able to find a good use for them in your applications. Look out for the next article, where I will show you some menus and cool views you can use!

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