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android:layout_span="2"/>

</TableRow>

</TableLayout>

TableLayout and TableRow

After examining main.xml, you can gather that the TableLayout and TableRow are

straightforward to use. You create the TableLayout once, then insert a TableRow. Now

you are free to insert any other widgets, such as TextView, EditView, and so on, inside

this TableRow.

Do look at the attributes, especially android:stretchColumns, android:layout_column,

and android:layout_span, which allow you to place widgets the same way you would

use a regular HTML table. I recommend that you follow the links to these attributes

and read up on how they work for a TableLayout.

Controlling input values

Controlling input values: Look at the EditText widget in the main.xml file at

. This

is the first text field for entering the “Total Amount” of the check. We want only num-

bers here. We can accept decimal numbers because real restaurant checks can be for

dollars and cents, and not just dollars. So we use the android:numeric attribute with a

value of decimal. This will allow whole values like 10 and decimal values like 10.12,

but will prevent any other type of entry.

This is a simple and concise way to control input values, thus saving us the trouble of

writing validation code in the Tipster.java file, and ensuring that the user does not enter

erroneous values. This XML-based constraints feature of Android is quite powerful and

useful. You should explore all possible attributes that go with a particular widget to

extract maximum benefits from this XML shorthand way of setting constraints. In a

future release, unless I have missed it completely in this release, I hope that Android

allows for entering ranges for the android:numeric attribute so that we can define what

range of numbers we wish to accept.

Since ranges are not currently available (to the best of my knowledge), you will see later

on that we do have to check for certain values like zero or empty values to ensure that

our tip calculation arithmetic does not fail.

Examining Tipster.java

Now we will look at the Tipster.java file which controls our application. This is the

main class that does the layout, the event handling, and the application logic.

The Android Eclipse plug-in creates the Tipster.java file in our project with the default

code shown in Example 1-7.

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O'Reilly 9781449388416 Datasheet Page 62