Multiline messages and timers.

Multi line text boxes

The simple text box we have met in the previous lecture has an interesting property Multiline. This is a boolean property, which being set to true allows the text box to span multiple lines. The default value is false. Another boolean property AcceptReturn, if set to true, pressing Enter creates a new line line the text box, if that text box spans multiple lines. Otherwise, pressing Enter clicks the default button of the form. For multiple line text boxes we can set scroll bars. The corresponding property is ScrollBars it can take one of the values none, horizontal, vertical, or both.

Now please create a form that looks like one shown on the picture below:

Create a form with multiple line text box
where the big square grey area on the left of the buttons is a usual text area with the following properties set:
Property Value Description
(Name) LogBox sets the name of the textbox
Multiline true can span multiple lines
ScrollBars Vertical show the vertical scroll bar
ReadOnly true doesn't let the user to type in the text box
Text   initially shows nothing
Width 400 width of the text box
Height 250 height of the text box

Now, we can use this text box LogBox as a output console. Double click on the Start button of your form and enter the following code in the body of the buttoc1_Click() function: 

static int i = 1;
LogBox->Text = String::Concat(LogBox->Text, S"Message #", i.ToString(), S"\r\n");
i++;
If you now run your new project, then every click on the Start button will add a new line like "Message #13" to the text box.

Timers

If we do not want to click on the Start button over and over, we can ask the program periodically call a function that would add the next message (or do something useful, for that matter). In order to do that, choose the Timer on the Toolbox panel and click on your form. A new Timer element appears in the area below the form:
Timer element appears below the form

In the Tool panel set the following properties of the timer element:
Property Value Description
(Name) NextStepTimer sets the name of the timer
Interval 500 set the interval between calls to 500 milliseconds
Enabled false initially timer is not active
Click twice on the icon of the timer element and copy the code from the button1_Click() function into the NextStepTimer_Tick() function. When the timer starts it will add a new message to the log text box every half of a second.

To start the timer, all we need to do is to set the value of the property Enabled to true. The function which is called by the Start button would be a good place to do that. Double click on the Start button on your form and enter the code: 

NextStepTimer->Enabled = true;

Numeric up and down boxes, how to change timer's interval

If we need to print our message more or less often, we need to change the value of the Interval property of the timer element. We can do that while the program is running. Let's modify the from by adding NumericUpDown element from the Toolbox
Numeric Up and Down element
Please set the following properties of the element:

Property Value Description
(Name) TimerUpDown sets the name of the numeric up and down element
Minimum 50 set the minimal value of the variable to 50 (ms)
Maximum 60000 set the maximum value of the interval to 60000 (ms)
Increment 25 set the increment/decrement of the variable to 25 (ms)
Value 500 set the initial value of the variable to 500 (ms)
ReadOnly true do not let the user type in this numeric text box, let him use the arrows only

The last step would be to connect the value in the numeric up and down. Double click on the numeric up/down element on your form and in the function TimerUpDown_ValueChanged() enter the following code: 
NextStepTimer->Interval = Convert::ToInt32( TimerUpDown->Value );
Now, every click on the numeric up/down element will change the displayed value and call the function TimerUpDown_ValueChanged(), which will read the changed value and reset the timer interval.

Homework assignment

To demonstrate that you understand the material presented in the last two lectures, add a new button Pause to the form and do the following: