Tk - Events

Events in its simplest form is handled with the help of commands. A simple example for event handling is event handling with button 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