State Variables

State variables are named memory locations with a specified data type which may have associated state transitions.

Note: If you are new to variables, see Variables Explained.

A state variable is a named area of device memory containing a value of a specified type, almost exactly like a regular variable. See Variables. The main difference is that a state variable may have one or more associated state transitions. See State Transitions.

In UJML, a state variable is declared using a state-var element inside of a state-variables element. See state-var, state-variables. A state variable must have a valid name and data type. See Identifiers, Data Types. Variable scope is determined by the element containing the state-variables element in which the state-var is declared. See Data Scoping and Sharing.

Note: All UJML data types are valid for a state variable except reference. See reference data type.

Assigning values

A state variable may be assigned the value of another variable, a literal, a function call result, or an expression of the proper data type. Until the state variable is assigned an initial value, it has a default value assigned when the state variable was created.

Data Type	Default Value
boolean	false
int	0
string	"" (Empty string)

Array variables

A state variable may be defined as an array using the size attribute of the state-var element. See Arrays. Any one array element acts exactly like a simple state variable of the same data type. Array state variables may not be assigned to or passed as function arguments without specifying an array element.

State variable lifetime

A state variable exists in memory for the lifetime of the application.

State variables and functions

A state variable may not be declared inside of a function element. See User Defined Functions. You may pass the value of a state variable to a function, as a parameter, exactly like a regular variable. See Using Functions.

Example

The following example shows how to declare two boolean state-variables. It is part of the helloworld4.ujml sample.

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<state-variables>
    <state-var name="sHelloBox" type="boolean"/>
    <state-var name="sInput" type="boolean" />
</state-variables>

The following example shows how to set the state-variables declared above to a boolean literal to start the application. It is part of the helloworld4.ujml sample.

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sHelloBox = true;
sInput = true;

The following example shows how to handle an onSelect event for the left-arrow button by updating a position variable and resetting the sHelloBox state variable using the _clear_state() function to move the visual elements displayed by the transition element. It is part of the helloworld4.ujml sample.

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<event name="onSelect">
    <accelerators>
        <key>LEFT</key>
    </accelerators>
    <script>
        mPosX = mPosX - &MOVEMENT;;
        if (mPosX &_LT; 0)
        {
            mPosX = 0;
        }
        _clear_state(sHelloBox);
        sHelloBox = true;
    </script>
</event>

The following example shows how to handle a state transition for the 'sHelloBox' state-variable by displaying a round-box containing a label. It is part of the helloworld4.ujml sample.

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<state var="sHelloBox">
    <transition value="true">
        <display>
            <!-- Say Hello on the screen using a label inside of a box. -->
            <round-box>
                <x><eval>mPosX</eval></x>
                <y><eval>mPosY</eval></y>
                <width>
                    <eval>mWidth</eval>
                </width>
                <height>
                    <eval>mHeight</eval>
                </height>
                <fg>&_COLOR_GRAY;</fg>
                <bg>&_COLOR_PURPLE;</bg>
                <x-arc-width>8</x-arc-width>
                <label>
                    <text>&SALUTATION;</text>
                    <x>&SPACING;</x>
                    <y>&SPACING;</y>
                    <fg>&_COLOR_WHITE;</fg>
                    <size>&_FONT_SIZE_LARGE;</size>
                    <style>&_FONT_STYLE_ITALIC;</style>
                    <face>&_FONT_FACE_SYSTEM;</face>
                </label>
            </round-box>
        </display>
    </transition>
</state>