Sunday, July 12, 2009

A Custom ListView for Android

I have been thinking about starting a new blog for Android stuff for quite a long time. And today, I found some time for the same. So here goes my first post. This is about developing your own custom list view. The List View is a very powerful UI element for the android platform. And it provides a lot of customizing features as well. Let’s jump into the details right away.
For this example, I will be using an example for a phone book entry, with the contacts having basic information like “name”, “phone” and “email”.

Step 1: Lets create a POJO class for the phone book.
Class name :
Not a complex code. Just the three fields, a constructor and the getters and setters. That’s it.
Step 2: Lets create the layout that each row of the List View is going to look like. I prefer to do this layout in xml rather than through coding/programmatically. xml stuff is pretty easy to develop.
File name : phone_row.xml 

This layout has three Text Views, tvContact, tvMobile and tvMail which we will be using in our code. We don’t need to touch any other elements from this file, if you should have to edit this xml, do it carefully.

Step 3: Now, lets create a class which our custom adapter will be calling to render each row of the List View. Here, we need the layout file created in Step 2. This class should extend any layout type, e.g, LinearLayout, TableLayout, etc. In my example, I am using a LinearLayout.

Class name :
In this class, create a constructor with two parameters, Context and the Pojo class Phonebook. And, inside the constructor, set the fields to the text views. The “this.setTag(entry)” will enable us to get info on the phonebook entry, when we use the listener for List View.

Update: I have deleted this class from the example, and have used the efficient way recommended for ListView. Checkout out the code.

Step 4: Now, create the Phonebook adapter class which extends the BaseAdapter. This will be used to set a list of Phonebook items to the list view with our customized layout.

Class name :
This class has a bit of coding, and changes to be made in the default methods that comes in when you extend the BaseAdapter class, however it is simple enough. A new constructor and two new private members is all that you have to include.
Custom List ViewOverride the methods as given in the code. The method getView is the important one. Here, we call our PhonebookAdapterView class.

Now, you are done. Your custom list view has been created. The final step would be testing the custom list view. Just create and activity with a listview. Then create an instance of the PhonebookAdapter class passing the parameters (Context and list of Phonebook objects)

Then, set this adapter to the list view. You are done. Here is the output.
Here is the link where you can find all the source code as an Android Project (1.5 compatible).

 Full source code is here.

Update: I have updated the example, to include a button on each line item, which when clicked, removes that item from the List View.