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CanvasRenderingContext2D.drawFocusIfNeeded()

CanvasRenderingContext2D.drawFocusIfNeeded() 是 Canvas 2D API 用来给当前路径或特定路径绘制焦点的方法,如果给定的元素获取了焦点。

语法

void ctx.drawFocusIfNeeded(element);
void ctx.drawFocusIfNeeded(path, element);

参数

element
是否需要设置焦点的元素。
path
Path2D 路径。

示例

使用 drawFocusIfNeeded 方法

这是一段使用 drawFocusIfNeeded 方法的简单的代码片段。

HTML

<canvas id="canvas">
  <input id="button" type="range" min="1" max="12">
</canvas>

JavaScript

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var button = document.getElementById("button");

button.focus();

ctx.beginPath();
ctx.rect(10, 10, 30, 30);
ctx.drawFocusIfNeeded(button);

修改下面的代码并在线查看 canvas的变化:

Playable code
<canvas id="canvas" width="400" height="200" class="playable-canvas">
<input id="button" type="range" min="1" max="12">
</canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
ctx.beginPath();
ctx.rect(10, 10, 30, 30);
ctx.drawFocusIfNeeded(button);</textarea>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var button = document.getElementById("button");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;
button.focus();

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);

规范描述

Specification Status Comment
WHATWG HTML Living Standard
CanvasRenderingContext2D.drawFocusIfNeeded
Living Standard  

浏览器兼容性

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) 29 (29)[1] 未实现 (Yes) (Yes)
Path parameter (Yes) 未实现 未实现 (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) 29.0 (29)[1] 未实现 (Yes) (Yes)
Path parameter (Yes) (Yes) 未实现 未实现 (Yes) (Yes)

兼容性注解

  • [1] 在 Gecko 28 (Firefox 28 / Thunderbird 28 / SeaMonkey 2.25 / Firefox OS 1.3)中, 此方法通过 "drawSystemFocusRing" 实现, 但是在 Gecko 29 (Firefox 29 / Thunderbird 29 / SeaMonkey 2.26)中已经改名。
  • [1] 在 Gecko 32 (Firefox 32 / Thunderbird 32 / SeaMonkey 2.29 / Firefox OS 2.0) 之前,此方法默认是无效的,受控于 flag "canvas.focusring.enabled"标识。

参见

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