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My first meeting with the SimpleAdapter widget

Such a shame. Normally, Android developers have their SimpleAdapter adventures right at the beginning of their Android development career, meanwhile I met this beast just now. I wouldn't say that this UI feature is overdocumented and that there are truckloads of example programs out there (if there are, Google does not find them) so I decided to share my experiences with whoever cares to read this blog entry.

It all started with a very simple wish that I wanted to create a list like this:


Each list entry has two lines and the lines are styled differently. Fortunately, there is an example program at the ListActivity documentation page which happens not to work and takes the input behind the list from a database. So it took me some time to find my friend, the SimpleAdapter widget and to find out, how to use it.

You can download the example program from here.

The root of the problem is that each element of this list is a complex view, consisting of two TextViews (XML mangling because of blog engine limitations):

[?xml version="1.0" encoding="utf-8"?]
[LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical"]

[TextView android:id="@+id/text1"
android:textSize="16px"
android:textStyle="bold"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/]

[TextView android:id="@+id/text2"
android:textSize="12px"
android:textStyle="italic"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/]
[/LinearLayout]

The corresponding SimpleAdapter maps an element from list of objects to this view.

SimpleAdapter notes = new SimpleAdapter(
this,
list,
R.layout.main_item_two_line_row,
new String[] { "line1","line2" },
new int[] { R.id.text1, R.id.text2 } );

Now this is not a trivial line of code. What it says is:

  • "list" is a reference to an object implementing the List interface. Each element in this list is an object implementing the Map interface. In our implementation example, the list is ArrayList and the elements in this list are HashMaps.
  • The layout describing one row in the main list is defined in layout/main_item_two_line_row.xml file.
  • In each individual HashMap, there are two key-value pairs. The keys are "line1" and "line2", the corresponding values are arbitrary objects whose toString() method yields the value displayed in the list row. In our case, the values are Strings.
  • Values stored with key "line1" will be displayed in the TextView whose id is "text1". Similarly, "line2" Map key is associated with "text2" TextView.
You can try the program following the instructions in the Start here entry. You can add items to the list using the menu.

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