组件实现随手拖动松手后贴边效果

问题现象
如何实现手指长按组件时，组件能够跟随手指拖动，手指抬起后，组件贴边停靠的效果。

背景知识
onTouch是用于处理触摸事件的组件属性，支持TouchType.Down（按下）、TouchType.Move（移动）、TouchType.Up（抬起），用于多模交互场景（如拖拽、点击、滑动等）。
animateTo是用于实现动画效果的核心函数，支持平滑过渡、弹性动画、曲线控制等。
解决方案
为实现上述功能，可通过如下步骤实现：

通过组件的触摸事件onTouch，其中使用TouchType.Down记录手指按下时的初始坐标，使用TouchType.Move获取手指移动时的位置信息，通过获取的位置信息修改组件的position属性实现元素的拖拽功能：
// 指针按下事件：记录初始坐标
case TouchType.Down: {
this.windowStartX = event.touches[0].windowX;
this.windowStartY = event.touches[0].windowY;
break;
}
case TouchType.Move: {
const windowX: number = event.touches[0].windowX;
const windowY: number = event.touches[0].windowY;
// 左边距吸附时：更新左边缘位置
if (this.edge.left !== undefined) {
this.edge.left = this.edge.left as number + (windowX - this.windowStartX);
}
// 右边距吸附时：更新右边缘位置
else {
this.edge.right = this.edge.right as number - (windowX - this.windowStartX);
}
// 更新顶部位置
this.edge.top = this.edge.top as number + (windowY - this.windowStartY);
// 更新起始坐标用于下次计算
this.windowStartX = windowX;
this.windowStartY = windowY;
break;
}
再通过TouchType.Up（手指抬起），对比手指抬起时组件所处位置，与容器组件的中心位置，判断出需要向哪边进行贴边操作，或与容器元素宽度进行对比，判断元素是否超出容器，选择将组件position属性的left或right设置为undefined并将其对立方向设置为0，且位置的调整设置于animateTo中，实现将元素从容器内部或容器外部缓慢调整至容器边缘，从而实现组件拖拽后的贴边效果：
case TouchType.Up: {
// 计算悬浮窗中心点在父组件中的水平坐标
let centerX: number;
if (this.edge.left !== undefined) {
centerX = this.edge.left as number + this.floatWindowWidth / 2;
} else {
centerX = this.containerWidth - (this.edge.right as number) - this.floatWindowWidth / 2;
}
// 使用阻尼动画实现吸附效果
this.uiContext.animateTo({ curve: curves.springMotion() }, () => {
// 获取屏幕宽度
let width = this.uiContext.px2vp(display.getDefaultDisplaySync().width);
// 启用吸附功能时
if (this.openAdsorb) {
// 根据中心点位置决定吸附方向
if (centerX > (this.containerWidth / 2)) {
// 右侧吸附
this.edge.right = this.pagePadding;
this.edge.left = undefined;
} else {
// 左侧吸附
this.edge.right = undefined;
this.edge.left = this.pagePadding;
}
} else {
// 检查是否超出左侧屏幕
let overflowLeft = this.edge.right! > width - this.floatWindowWidth;
// 检查是否超出右侧屏幕
let overflowRight = this.edge.right! < 0;
// 处理超出屏幕边界的情况
if (overflowLeft) { // 超出左边屏幕
this.edge.left = undefined;
this.edge.right = width - this.floatWindowWidth;
} else if (overflowRight) { // 超出右边屏幕
this.edge.right = this.pagePadding;
this.edge.left = undefined;
}
}
})
break;
}
完整实现如下：

import { curves, display } from '@kit.ArkUI';

@Component
export struct FloatWindowView {
@State edge: Edges = { top: 200, left: 0 };
@Link containerWidth: number;
@Link containerHeight: number;
private windowStartX: number = 0;
private windowStartY: number = 0;
// 是否启用吸附功能
openAdsorb: boolean = true;
@Prop pagePadding: number = 0; // 页面内容内边距，用于悬浮窗位置计算
@State floatWindowWidth: number = 100; // 悬浮窗宽度
@State floatWindowHeight: number = 50; // 悬浮窗高度
uiContext: UIContext = this.getUIContext();

// 触摸回调，实现悬浮窗跟手拖拽和贴边吸附动画
onTouchEvent(event: TouchEvent): void {
switch (event.type) {
// 指针按下事件：记录初始坐标
case TouchType.Down: {
this.windowStartX = event.touches[0].windowX;
this.windowStartY = event.touches[0].windowY;
break;
}
case TouchType.Move: {
const windowX: number = event.touches[0].windowX;
const windowY: number = event.touches[0].windowY;
// 左边距吸附时：更新左边缘位置
if (this.edge.left !== undefined) {
this.edge.left = this.edge.left as number + (windowX - this.windowStartX);
}
// 右边距吸附时：更新右边缘位置
else {
this.edge.right = this.edge.right as number - (windowX - this.windowStartX);
}
// 更新顶部位置
this.edge.top = this.edge.top as number + (windowY - this.windowStartY);
// 更新起始坐标用于下次计算
this.windowStartX = windowX;
this.windowStartY = windowY;
break;
}
// 指针抬起事件：实现吸附动画和边界限制
case TouchType.Up: {
// 计算悬浮窗中心点在父组件中的水平坐标
let centerX: number;
if (this.edge.left !== undefined) {
centerX = this.edge.left as number + this.floatWindowWidth / 2;
} else {
centerX = this.containerWidth - (this.edge.right as number) - this.floatWindowWidth / 2;
}
// 使用阻尼动画实现吸附效果
this.uiContext.animateTo({ curve: curves.springMotion() }, () => {
// 获取屏幕宽度
let width = this.uiContext.px2vp(display.getDefaultDisplaySync().width);
// 启用吸附功能时
if (this.openAdsorb) {
// 根据中心点位置决定吸附方向
if (centerX > (this.containerWidth / 2)) {
// 右侧吸附
this.edge.right = this.pagePadding;
this.edge.left = undefined;
} else {
// 左侧吸附
this.edge.right = undefined;
this.edge.left = this.pagePadding;
}
} else {
// 检查是否超出左侧屏幕
let overflowLeft = this.edge.right! > width - this.floatWindowWidth;
// 检查是否超出右侧屏幕
let overflowRight = this.edge.right! < 0;
// 处理超出屏幕边界的情况
if (overflowLeft) { // 超出左边屏幕
this.edge.left = undefined;
this.edge.right = width - this.floatWindowWidth;
} else if (overflowRight) { // 超出右边屏幕
this.edge.right = this.pagePadding;
this.edge.left = undefined;
}
}
})
break;
}
default: {
break;
}
}
}

build() {
Column() {
}
.clip(true)
.backgroundColor('#0A59F7')
.width(this.floatWindowWidth)
.height(this.floatWindowHeight)
.position(this.edge)
.onTouch((event: TouchEvent) => {
this.onTouchEvent(event);
})
}
}

@Entry
@Component
struct Index {
// 父组件宽度
@State containerWidth: number = 0;
// 父组件高度
@State containerHeight: number = 0;

build() {
Stack() {
FloatWindowView({
containerWidth: this.containerWidth, // 传递父容器宽度
containerHeight: this.containerHeight, // 传递父容器高度
})
.width('100%')
}
// 设置外层Stack容器的尺寸
.height('100%')
.width('100%')

.onAreaChange((oldValue: Area, newValue: Area) => {  
  // 记录父组件的宽高  
  if (oldValue.width !== newValue.width) {  
    this.containerWidth = newValue.width as number;  
  }  

  if (oldValue.height !== newValue.height) {  
    this.containerHeight = newValue.height as number;  
  }  
})  

}
}
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