Learning MIT App Inventor: A Hands-On Guide to Building Your Own Android Apps

Global Variables

Global variables need to be initialized before they can be used. The initialize global block does three things: creates the variable, gives it a name, and sets its initial value.

Choose the initialize block from the Variables built-in menu, and then click in the Name field to replace the word name with a useful name. The initialize block must have an initial value. This is similar to setting a value of a component property in the Designer; you have to put in something for the app to have in that variable when it starts. A variable cannot be truly empty.

Usually, the value given to the initialize block is useful and relevant, such as setting a counter variable to start at zero. Sometimes you just need space for later and you ...