Svelte延时过渡

Svelte 延时过渡

Svelte 过渡引擎其中一项特别强大的功能就是可以设置延时（defer） 过渡，以便多个效果之间协调。以这todo lists为例， 在其中更换todo将其发送到相对的列表中。在真实世界中，物体的移动不是这般生硬，它们是有其运动轨迹，而不像这般突然出现。给程序添加运动效果能更好的帮助用户了解程序界面变化。我们可以使用crossfade 函数来实现此效果，该函数创建一对称名为 send 和receive. 当一个标签被 'sent'时， 它会寻找一个被'received'的标签，并赋予一个过渡效果，反之同理。如果没有对应的接收方，过渡效果将会设置为fallback 。在65行找到 <label>标签， 给它添加send 和 receive 过渡：<label

in:receive="{{key: todo.id}}"

out:send="{{key: todo.id}}"

>对下一个 <label> 标签执行相同的操作：<label

class="done"

in:receive="{{key: todo.id}}"

out:send="{{key: todo.id}}"

>现在，当您切换列表项时，它们会平滑移动到新位置，没有添加过渡效果的标签仍然笨拙地跳来跳去，我们将下一章中解决它。示例代码App.svelte<script>

import { quintOut } from 'svelte/easing';

import { crossfade } from 'svelte/transition';

const [send, receive] = crossfade({
    duration: d => Math.sqrt(d * 200),
    fallback(node, params) {
        const style = getComputedStyle(node);
        const transform = style.transform === 'none' ? '' : style.transform;
        return {
            duration: 600,
            easing: quintOut,
            css: t => `
                transform: ${transform} scale(${t});
                opacity: ${t}
            `
        };
    }
});
let uid = 1;
let todos = [
    { id: uid++, done: false, description: 'write some docs' },
    { id: uid++, done: false, description: 'start writing blog post' },
    { id: uid++, done: true,  description: 'buy some milk' },
    { id: uid++, done: false, description: 'mow the lawn' },
    { id: uid++, done: false, description: 'feed the turtle' },
    { id: uid++, done: false, description: 'fix some bugs' },
];
function add(input) {
    const todo = {
        id: uid++,
        done: false,
        description: input.value
    };
    todos = [todo, ...todos];
    input.value = '';
}
function remove(todo) {
    todos = todos.filter(t => t !== todo);
}
function mark(todo, done) {
    todo.done = done;
    remove(todo);
    todos = todos.concat(todo);
}

</script>

<div class='board'>

<input

placeholder="what needs to be done?"

on:keydown={e => e.which === 13 && add(e.target)}

>

<div class='left'>
    <h2>todo</h2>
    {#each todos.filter(t => !t.done) as todo (todo.id)}
        <label
            in:receive="{{key: todo.id}}"
            out:send="{{key: todo.id}}"
        >
            <input type=checkbox on:change={() => mark(todo, true)}>
            {todo.description}
            <button on:click="{() => remove(todo)}">remove</button>
        </label>
    {/each}
</div>
<div class='right'>
    <h2>done</h2>
    {#each todos.filter(t => t.done) as todo (todo.id)}
        <label
            class="done"
            in:receive="{{key: todo.id}}"
            out:send="{{key: todo.id}}"
        >
            <input type=checkbox checked on:change={() => mark(todo, false)}>
            {todo.description}
            <button on:click="{() => remove(todo)}">remove</button>
        </label>
    {/each}
</div>

</div>

<style>

.board {

display: grid;

grid-template-columns: 1fr 1fr;

grid-gap: 1em;

max-width: 36em;

margin: 0 auto;

}

.board > input {
    font-size: 1.4em;
    grid-column: 1/3;
}
h2 {
    font-size: 2em;
    font-weight: 200;
    user-select: none;
    margin: 0 0 0.5em 0;
}
label {
    position: relative;
    line-height: 1.2;
    padding: 0.5em 2.5em 0.5em 2em;
    margin: 0 0 0.5em 0;
    border-radius: 2px;
    user-select: none;
    border: 1px solid hsl(240, 8%, 70%);
    background-color:hsl(240, 8%, 93%);
    color: #333;
}
input[type="checkbox"] {
    position: absolute;
    left: 0.5em;
    top: 0.6em;
    margin: 0;
}
.done {
    border: 1px solid hsl(240, 8%, 90%);
    background-color:hsl(240, 8%, 98%);
}
button {
    position: absolute;
    top: 0;
    right: 0.2em;
    width: 2em;
    height: 100%;
    background: no-repeat 50% 50% url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24'%3E%3Cpath fill='%23676778' d='M12,2C17.53,2 22,6.47 22,12C22,17.53 17.53,22 12,22C6.47,22 2,17.53 2,12C2,6.47 6.47,2 12,2M17,7H14.5L13.5,6H10.5L9.5,7H7V9H17V7M9,18H15A1,1 0 0,0 16,17V10H8V17A1,1 0 0,0 9,18Z'%3E%3C/path%3E%3C/svg%3E");
    background-size: 1.4em 1.4em;
    border: none;
    opacity: 0;
    transition: opacity 0.2s;
    text-indent: -9999px;
    cursor: pointer;
}
label:hover button {
    opacity: 1;
}

</style>