Events in its simplest form is handled with the help of commands In Tk. A simple example for event handling is event handling with button of Tk events and is shown below −
#!/usr/bin/wish
proc myEvent { } {
puts "Event triggered"
}
pack [button .myButton1 -text "Button 1" -command myEvent]
When we run the above program, we will get the following output −
A simple program to show delay text animation event is shown below −
#!/usr/bin/wish
proc delay {} {
for {set j 0} {$j < 100000} {incr j} {}
}
label .myLabel -text "Hello................" -width 25
pack .myLabel
set str "Hello................"
for {set i [string length $str]} {$i > -2} {set i [expr $i-1]} {
.myLabel configure -text [string range $str 0 $i]
update
delay
}
When we run the program, we will get the following output in animated way −
Event after delay
The syntax for event after delay is shown below −
after milliseconds number command
A simple program to show after delay event is shown below −
#!/usr/bin/wish
proc addText {} {
label .myLabel -text "Hello................" -width 25
pack .myLabel
}
after 1000 addText
When we run the program, we will get the following output after one second −
You can cancel an event using the after cancel command as shown below −
#!/usr/bin/wish
proc addText {} {
label .myLabel -text "Hello................" -width 25
pack .myLabel
}
after 1000 addText
after cancel addText
Event Binding
The syntax for event binding is as shown below −
bind arguments
Keyboard Events Example
#!/usr/bin/wish
bind . {puts "Key Pressed: %K "}
When we run the program and press a letter X, we will get the following output −
Key Pressed: X
Mouse Events Example
#!/usr/bin/wish
bind . {puts "Button %b Pressed : %x %y "}
When we run the program and press the left mouse button, we will get an output similar to the following −
Button 1 Pressed : 89 90
Linking Events with Button Example
#!/usr/bin/wish
proc myEvent { } {
puts "Event triggered"
}
pack [button .myButton1 -text "Button 1" -command myEvent]
bind . ".myButton1 invoke"
When we run the program and press enter, we will get the following output −
Event triggered
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