使用 React 实现拖放的技术要点
1.如何使用 React 的鼠标事件系统
2.如何判断拖放开始和拖放结束
3.如何实现拖放元素的位置移动 (可分为两种，一种是直接拖着具体要被移动的dom移动；另外一种是具体dom留在原位，拖着具体dom的影子移动，确定位置后，再将具体的dom放过去)
4.拖放状态在组件中如何维护
鼠标移动可能会超出要移动的组件和他的父组件，除了在document上监听，还可以在一个全局透明遮罩层上监听MouseMove和MouseUp好处：拖放过程不会选中其他任何元素，防止点击到其他组件
其他情景思考：
每个条目高度不一致，如何确定移动位置？
条目所在的列表有折叠，存在滚动条，如何根据滚动条确定位置？1
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import React, { Component } from "react";
require("./DndSample.css");
const list = [];
for (let i = 0; i < 10; i++) {
list.push(`Item ${i + 1}`);
}
const move = (arr, startIndex, toIndex) => {
arr = arr.slice();
arr.splice(toIndex, 0, arr.splice(startIndex, 1)[0]);
return arr;
};
const lineHeight = 42;
class DndSample extends Component {
constructor(props) {
super(props);
this.state.list = list;
}
state = {
dragging: false,
draggingIndex: -1,
startPageY: 0,
offsetPageY: 0,
};
handleMounseDown = (evt, index) => {
this.setState({
dragging: true,
startPageY: evt.pageY,
currentPageY: evt.pageY,
draggingIndex: index,
});
};
handleMouseUp = () => {
this.setState({ dragging: false, startPageY: 0, draggingIndex: -1 });
};
//如果往下滑，就一次把下一条数据交换位置，如果往上移动，就一次把上一条数据交换位置，
handleMouseMove = evt => {
let offset = evt.pageY - this.state.startPageY;
const draggingIndex = this.state.draggingIndex;
if (offset > lineHeight && draggingIndex < this.state.list.length - 1) {
// move down
offset -= lineHeight;
this.setState({
list: move(this.state.list, draggingIndex, draggingIndex + 1),
draggingIndex: draggingIndex + 1,
startPageY: this.state.startPageY + lineHeight,
});
} else if (offset < -lineHeight && draggingIndex > 0) {
// move up
offset += lineHeight;
this.setState({
list: move(this.state.list, draggingIndex, draggingIndex - 1),
draggingIndex: draggingIndex - 1,
startPageY: this.state.startPageY - lineHeight,
});
}
this.setState({ offsetPageY: offset });
};
getDraggingStyle(index) {
if (index !== this.state.draggingIndex) return {};
return {
backgroundColor: "#eee",
transform: `translate(10px, ${this.state.offsetPageY}px)`,
opacity: 0.5,
};
}
render() {
return (
<div className="dnd-sample">
<ul>
{this.state.list.map((text, i) => (
<li
key={text}
onMouseDown={evt => this.handleMounseDown(evt, i)}
style={this.getDraggingStyle(i)}
>
{text}
</li>
))}
</ul>
{this.state.dragging && ( //在一个遮罩层上监听MouseMove和MouseUp
<div
className="dnd-sample-mask"
onMouseMove={this.handleMouseMove}
onMouseUp={this.handleMouseUp}
/>
)}
</div>
);
}
}
export default DndSample;
1 | .dnd-sample ul { |