CanvasRenderingContext2D: drawFocusIfNeeded() 方法

基线 广泛可用

此功能已十分成熟，可在许多设备和浏览器版本中使用。它自 2015 年 7 月.

反馈

语法

CanvasRenderingContext2D.drawFocusIfNeeded() 方法是 Canvas 2D API 的方法，如果指定元素获得焦点，则会在当前或给定的路径周围绘制焦点环。
drawFocusIfNeeded(element)
drawFocusIfNeeded(path, element)

js

参数

element

要检查其是否获得焦点的元素。

path

要使用的 Path2D 路径。

返回值

示例

无 (undefined).

管理按钮焦点

HTML

此示例在画布上绘制两个按钮。drawFocusIfNeeded() 方法用于在适当的时候绘制焦点环。
<canvas id="canvas">
  <button id="button1">Continue</button>
  <button id="button2">Quit</button>
</canvas>

JavaScript

CanvasRenderingContext2D.drawFocusIfNeeded() 方法是 Canvas 2D API 的方法，如果指定元素获得焦点，则会在当前或给定的路径周围绘制焦点环。
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
const button1 = document.getElementById("button1");
const button2 = document.getElementById("button2");

document.addEventListener("focus", redraw, true);
document.addEventListener("blur", redraw, true);
canvas.addEventListener("click", handleClick, false);
redraw();

function redraw() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  drawButton(button1, 20, 20);
  drawButton(button2, 20, 80);
}

function handleClick(e) {
  // Calculate click coordinates
  const x = e.clientX - canvas.offsetLeft;
  const y = e.clientY - canvas.offsetTop;

  // Focus button1, if appropriate
  drawButton(button1, 20, 20);
  if (ctx.isPointInPath(x, y)) {
    button1.focus();
  }

  // Focus button2, if appropriate
  drawButton(button2, 20, 80);
  if (ctx.isPointInPath(x, y)) {
    button2.focus();
  }
}

function drawButton(el, x, y) {
  const active = document.activeElement === el;
  const width = 150;
  const height = 40;

  // Button background
  ctx.fillStyle = active ? "pink" : "lightgray";
  ctx.fillRect(x, y, width, height);

  // Button text
  ctx.font = "15px sans-serif";
  ctx.textAlign = "center";
  ctx.textBaseline = "middle";
  ctx.fillStyle = active ? "blue" : "black";
  ctx.fillText(el.textContent, x + width / 2, y + height / 2);

  // Define clickable area
  ctx.beginPath();
  ctx.rect(x, y, width, height);

  // Draw focus ring, if appropriate
  ctx.drawFocusIfNeeded(el);
}

html

规范

结果
规范
# HTML 标准

浏览器兼容性

dom-context-2d-drawfocusifneeded-dev

另请参阅