我决定重写这个问题。我试图说清楚简短，但它没有成功。
我想要实现的是一个可以放在任何物体上的物体（Rectangle，Image等等）并让它响应触摸手势。不幸的是我遇到了一个我无法解决的问题。我无法找到帮助，所以我在这里试试。
这里很简单main.qml：
import QtQuick 2.5
import QtQuick.Controls 1.3
import QtQuick.Window 2.2
import QtQuick.Dialogs 1.2
ApplicationWindow {
title: qsTr("Touch surface test")
width: 640
height: 480
visible: true
Rectangle {
width: 200
height: 60
color: "blue"
MyTouchSurface {
id: myTouchSurface
anchors.fill: parent
}
}
}
这是MyTouchSurface.qml
import QtQuick 2.5
MultiPointTouchArea {
id: myTouchSurface
// this is object I want to respond to touch gestures
property Item target: parent
// this is object I want to keep target in. I won't let target get out of it
property Item container: parent.parent
property double targetX: target.x
property double targetY: target.y
property double centerX: target.width / 2
property double centerY: target.height / 2
property double lastTouchX
property double lastTouchY
property double lastXDrag
property double lastYDrag
// here I calculate received touches and move target
onPressed: {
lastTouchX = touchPoints[0].sceneX
lastTouchY = touchPoints[0].sceneY
if (slidingAnimation.running)
slidingAnimation.stop()
}
onTouchUpdated: {
if (touchPoints.length) {
target.x += touchPoints[0].sceneX - lastTouchX
target.y += touchPoints[0].sceneY - lastTouchY
lastXDrag = touchPoints[0].sceneX - lastTouchX
lastYDrag = touchPoints[0].sceneY - lastTouchY
lastTouchX = touchPoints[0].sceneX
lastTouchY = touchPoints[0].sceneY
}
else
startSliding()
}
// when lifting fingers off screen I want to slide target across it's container
function startSliding() {
slidingAnimation.toX = target.x + lastXDrag * 10
slidingAnimation.toY = target.y + lastYDrag * 10
slidingAnimation.restart()
}
// This is animation responsible for sliding the target
ParallelAnimation {
id: slidingAnimation
property double toX
property double toY
property int animationDuration: 250
NumberAnimation {
target: myTouchSurface.target
property: "x"
to: slidingAnimation.toX
duration: slidingAnimation.animationDuration
easing.type: Easing.OutQuad
}
NumberAnimation {
target: myTouchSurface.target
property: "y"
to: slidingAnimation.toY
duration: slidingAnimation.animationDuration
easing.type: Easing.OutQuad
}
}
// this is how I keep target object within container
onTargetXChanged: {
if (container != null) {
if (target.x + centerX < 0)
target.x = -centerX
else if (target.x + centerX > container.width)
target.x = container.width - centerX
}
}
onTargetYChanged: {
if (container != null) {
if (target.y + centerY < 0)
target.y = -centerY
else if (target.y + centerY > container.height)
target.y = container.height - centerY
}
}
}
我想在MyTouchSurface中拥有所有计算和函数，因此很容易应用于其他对象并在另一个项目中使用它。
我遇到的问题是我不知道如何阻止目标对象移出容器。好吧，这里的代码工作得非常好，但它也会产生非常难看的关于绑定循环的错误。
发生的事情是：
所以我在问：是否有其他简单的方法可以防止对象飞离屏幕并且不会同时收到绑定循环错误？
我知道我可以使用Timer不时检查目标x和y，并将其带回来。
我知道我可以更改动画的easing和duration，使其在容器边界上停止，但看起来已停止。
严重。有没有简单的方法？
那些不起作用的事情：
x或y 谢谢大家帮助我。很高兴知道我并不孤单：）
答案 0 :(得分：2)
我认为您的问题是您在属性更新处理程序（targetX）内更新了target.x或y（对于onTargetXChanged()而言）。
这可能被QML引擎选为biding循环，就像你从target.x更改onTargetXChanged()一样，信号onTargetXChanged()将再次触发，因为它已绑定到它在财产double targetX: target.x。
您可以尝试这样的事情：
TouchArea {
property Item target // target is the Image object being moved
property double targetX: target.x
property double targetY: target.y
onTargetXChanged: {
/* if object is out of specified area move x respectively */
performPropertyUpdate(args)
}
onTargetYChanged: {
/* if object is out of specified area move y respectively */
performPropertyUpdate(args)
}
function performPropertyUpdate(args) {
/* actual setting of target.x or target.y */
}
}
答案 1 :(得分：2)
解决方案只需使用Connections：
import QtQuick 2.5
MultiPointTouchArea {
id: myTouchSurface
// this is object I want to respond to touch gestures
property Item target: parent
// this is object I want to keep target in. I won't let target get out of it
property Item container: parent.parent
property double targetX: target.x
property double targetY: target.y
property double centerX: target.width / 2
property double centerY: target.height / 2
property double lastTouchX
property double lastTouchY
property double lastXDrag
property double lastYDrag
// here I calculate received touches and move target
onPressed: {
lastTouchX = touchPoints[0].sceneX
lastTouchY = touchPoints[0].sceneY
if (slidingAnimation.running)
slidingAnimation.stop()
}
onTouchUpdated: {
if (touchPoints.length) {
target.x += touchPoints[0].sceneX - lastTouchX
target.y += touchPoints[0].sceneY - lastTouchY
lastXDrag = touchPoints[0].sceneX - lastTouchX
lastYDrag = touchPoints[0].sceneY - lastTouchY
lastTouchX = touchPoints[0].sceneX
lastTouchY = touchPoints[0].sceneY
}
else
startSliding()
}
// when lifting fingers off screen I want to slide target across it's container
function startSliding() {
slidingAnimation.toX = target.x + lastXDrag * 10
slidingAnimation.toY = target.y + lastYDrag * 10
slidingAnimation.restart()
}
// This is animation responsible for sliding the target
ParallelAnimation {
id: slidingAnimation
property double toX
property double toY
property int animationDuration: 250
NumberAnimation {
target: myTouchSurface.target
property: "x"
to: slidingAnimation.toX
duration: slidingAnimation.animationDuration
easing.type: Easing.OutQuad
}
NumberAnimation {
target: myTouchSurface.target
property: "y"
to: slidingAnimation.toY
duration: slidingAnimation.animationDuration
easing.type: Easing.OutQuad
}
}
Connections{
target:myTouchSurface.target
onXChanged:{
if (container != null) {
if (target.x + centerX < 0)
target.x = -centerX
else if (target.x + centerX > container.width)
target.x = container.width - centerX
}
}
onYChanged:{
if (container != null) {
if (target.y + centerY < 0)
target.y = -centerY
else if (target.y + centerY > container.height)
target.y = container.height - centerY
}
}
}
// this is how I keep target object within container
// onTargetXChanged: {
// }
// onTargetYChanged: {
// }
}
答案 2 :(得分：0)
要解决问题，myX应该是x，
property alias myX: rectangle2.x
您遇到此问题导致myX正在更改x的值，而x正在更改myX的值：循环。