Picker

So far in this book, we have used DatePickerIOS and DatePickerAndroid for users to select dates. Each platform also has access to a native Picker component, where we can populate an array of choices and allow our users to interact with it.

Building a Picker is easy. We start by writing a Picker in the render method of a component and populate it with Picker.Item children:

<Picker> 
  <Picker.Item  
    label='Hello' 
    value='hello' 
  /> 
</Picker>  

Then, we can give the Picker some props. The following ones are used in this exercise:

• onValueChange: This is a callback fired when an item has been selected. It passes two arguments: itemValue and itemPosition
• selectedValue: This is a reference to the current value of the Picker list

Selecting a category

We will modify our existing AddExpensesModal component to add the following functionality:

• Create a Button right below the ExpandableCell/DatePickerIOS component to select a category for our expense.
• On press, that button...