Stopping a behavior - QML - qt

Question

I program a "game" where a ball is sent to bounce against the walls.
Before hurt the walls, the behavior on y is a spring animation. When it hurt the wall, the ball should bounce and have a linear movement.
My problem is I can't stop the initial Behavior.
I have tried several way :
disabled the behavior but the movement in progress continue
stop the SpringAnimation : I have the error : " QML SpringAnimation: setRunning() cannot be used on non-root animation nodes."
This is the code
Rectangle {
id: ball
property bool enableMoving: false
function newMousePos(mX,mY){
if(enableMoving){
ball.x = mX - ball.width/2
ball.y = mY - ball.height/2
}
}
Behavior on x {enabled: true;id: behavX; SpringAnimation {id:spX; spring: 0.8; damping: 0.9; mass: 10; } }
Behavior on y {enabled: true;id: behavY; SpringAnimation {id:spY; spring: 0.8; damping: 0.9; mass: 10 ; } }
onXChanged: {
if(ball.x>main.width-ball.size) {
console.log("wall 2 ")
spX.stop(); spY.stop()
}
if(ball.x<0) {
...
}
}
onYChanged: {
...
}
Timer{
id:timerDisableMoving
interval: 500; running:true
onTriggered: enableMoving=false
}
}
I don't understand why I can't stop the behavior. Is it possible to define behavior on state to solve the problem ?

Answer 1

Put this code on signal when ball hits wall:
behavX.enabled = false
This will disable behavior (I have tested it in my project).
If you only want to disable specific animation then do it like this:
spX.running = false //ignore this, it is equivalent to spX.stop()
I just thought that you might putted code like this:
function disableBehavior()
{
behavX.enabled = false
//...
behavX.enabled = true
}
If this is the case, then it wont work because during the time of execution animation wont happen.
Instead, you should do asynchronous call, for example like this:
function disableBehavior()
{
behavX.enabled = false
//...
myTimer.start()
}
//...
Timer
{
id: myTimer
interval: 1
running: false
onTriggered:
{
behavX.enabled = true
stop()
}
}
But, I think that you will want to call "behavior enabler" after your "linear behavior" is finished (instead of creating new timer).

Answer 2

I think, I had similar problem. I had some Behavior, which animated change of some property. And I wanted to be able to stop it in the middle, while it did not yet complete.
It did not work. By the way, QML also was complaining in the console, that I try to use some method on non-root Animation.
The short answer:
It seems, that it is not supported by the Behavior to be stopped in the middle.
Though, it can be interrupted by setting new value to the property. This would restart the animation to target the new value. When I realized it, I implemented the "stop" function like this:
function stopAnimation() {
// disable animation for the next value change
moveBehavior.enabled = false
// Change value of the property of interest.
// This stops currently running animation
y += 1
// Restore initial value of the property
y -= 1
// Enable animation for subsequent property changes
moveBehavior.enabled = true
}
So, I disable the behavior to make the change of properties instant. Then I change target property to something very close to the current value (I believe, I cannot use the same value, because then "onChange" signal will not be emitted). At this point running animation should be stopped. Then I reset property to its original value. And then enable animation again to handle further property changes.
Looks not that good, but it worked for me with Behavior...
After thinking a bit more I come to the conclusion, that I probably should not use Behavior. Then I just created PropertyAnimation{} tied to my property of interest directly in the object, which needs to be moved. And then I just dynamically assign target value and duration and with now "start()" and "stop()" just work as expected.
Full solution looks like this (what it does, you can probably figure out):
Item {
id: root
focus: true
Rectangle {
id: racket
height: 40
width: 10
x: 20
y: 20
color: "blue"
property int maxY: 460
// ...
PropertyAnimation {
id: moveDownAnimation
target: racket
property: "y"
to: racket.maxY
// if you want constant velocity, you need
// to calculate duration dynamically based
// on desired velocity and distance
duration: 1000
}
function moveUp () { // just return racket to the initial position
y = 50
}
function moveDown() {
moveDownAnimation.start()
}
function stopAnimation() {
moveDownAnimation.stop()
}
}
Keys.onPressed: {
if (event.isAutoRepeat) {
return
}
if (event.key === Qt.Key_Q) {
racket.moveUp() // return to initial position
} else if (event.key === Qt.Key_A) {
racket.moveDown()
}
}
Keys.onReleased: {
if (event.isAutoRepeat) {
return
}
if (event.key === Qt.Key_A) {
racket.stopAnimation()
}
}
}