User's Guide
You are now ready to implement your design in the Public Interface
Editor. Begin by defining the attributes of your runner part. A
part's attributes typically correlate to the part's Attribute data
types and can additionally include derived attributes, or
attributes that are determined based on the value of other attributes.
In the Public Interface Editor, on the Attribute page of the
notebook, do the following:
- Type number in the Attribute name entry field and
select the Add with defaults push button.
Your Public Interface Editor will look like this:

Notice that several default values are displayed:
- number is the default Get selector and matches the
number method of your design. When your runner part is asked
for the value of its number attribute, it will run the
number method to answer the number that has been assigned to the
runner for the race.
- Likewise, number: is the default Set
selector. When your runner part is told the number that has been
assigned to it for the race, it uses the number: method to
store the value in its number attribute.
- number is the default Change event symbol.
Whenever a value is stored in the number attribute using the
number: set selector, the runner part signals this event to
let other parts know that the value has changed. For example, if there
is an attribute-to-attribute connection between number and a
label's string value, the label part will be informed so that it displays
the latest value.
- Object is the default Attribute data type.
This means that the number attribute must be an instance of the
Object class.
- You can change any of the default values if you need to. Change the
value in the Attribute data type field to String,
because in this example the runner's number is a simple three-character
string of numerals, and select the Update push button.
- Repeat the previous steps for the runner's finishTime
attribute. Type finishTime as the Attribute
name. Select Add with defaults, and change the
Attribute data type to Time, because the runner's
finish time is a time.
- The runner also has one derived attribute,
asResultString. Type this attribute name but do
not select Add with defaults. Instead, enter
asResultString as the Get selector, enter
runnerChanged as the Change event symbol, and enter
String as the Attribute data type. Ensure the
Set selector is blank. Then, select the Add push
button.
Every time the runner part receives the runnerChanged event, it
will refresh the value of its asResultString attribute by running
the asResultString get selector. Because there is no set
selector, the attribute is read-only, so other parts cannot set it.
Now is a good time to save your work. Select Save Part
from the File menu.
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