我正在使用 Javascript 编写一个小型移动应用程序。
我正在调用一个远程 API，该 API 会响应一些 JSON 格式的数据。在该数据中是我需要在我的应用程序中显示的产品图像的 URL。我已经将 JSON 解析为一个 JS 数组，现在有一个包含所有图像 URL 的数组。当我第一次加载我的应用程序时，我有一个 Canvas ，用于显示数组中的第一张图像。我有两个按钮，上一个和下一个。我希望能够通过使用数组中的 URL 在 Canvas 上绘制来使用这些按钮循环浏览图像。
有什么想法吗？
最佳答案
您正在寻找类似于以下内容的内容吗？
// Image URLs
var imageUrls = ['http://emojipedia-us.s3.amazonaws.com/cache/8b/bd/8bbd3405b0a197214e229428c23dbe60.png', 'http://emojipedia-us.s3.amazonaws.com/cache/05/d1/05d1ba284ee1a3bfe4e0f68988baafb9.png', 'http://emojipedia-us.s3.amazonaws.com/cache/99/4c/994c5997c7a509703cc53ec2000bb258.png', 'http://emojipedia-us.s3.amazonaws.com/cache/59/0c/590c832e73a472c416bf9d8bfdd02a4a.png'];
// Keep track of the index of the image URL in the array above
var imageShownIndex = 0;
// Create a canvas
var canvas = document.createElement('canvas');
var canvasContext = canvas.getContext('2d');
canvas.height = 150;
canvas.width = 150;
// Create a button that will load the previous image on the canvas when clicked
var previousButton = document.createElement('button');
previousButton.innerHTML = 'Previous Image';
previousButton.onclick = function () {
// Show images in a cycle, so when you get to the beginning of the array, you loop back to the end
imageShownIndex = (imageShownIndex==0) ? imageUrls.length-1 : imageShownIndex-1;
updateImage();
};
// Do same for the next button
var nextButton = document.createElement('button');
nextButton.innerHTML = 'Next Image';
nextButton.onclick = function () {
imageShownIndex = (imageShownIndex == imageUrls.length-1) ? 0 : imageShownIndex+1;
updateImage();
};
document.body.appendChild(previousButton);
document.body.appendChild(canvas);
document.body.appendChild(nextButton);
// Show the first image without requiring a click
updateImage();
function updateImage() {
// Create the Image object, using the URL from the array as the source
// You could pre-load all the images and store them in the array, rather than loading each image de novo on a click
var img = new Image();
img.src = imageUrls[imageShownIndex];
// Clear the canvas
canvasContext.clearRect(0, 0, 150, 150);
// After the image has loaded, draw the image on the canvas
img.onload = function() {
canvasContext.drawImage(img, 0, 0);
}
}编辑:或者如果您已经制作了 HTML 元素，您可以只使用 JavaScript 来控制 Canvas 。例如:
<html>
<body>
<button id="previous_button" onclick="goToPreviousImage()">Previous Image</button>
<canvas id="image_canvas" height=150, width=150></canvas>
<button id="next_button" onclick="goToNextImage()">Next Image</button>
</body>
<script>
var imageUrls = ['http://emojipedia-us.s3.amazonaws.com/cache/8b/bd/8bbd3405b0a197214e229428c23dbe60.png', 'http://emojipedia-us.s3.amazonaws.com/cache/05/d1/05d1ba284ee1a3bfe4e0f68988baafb9.png', 'http://emojipedia-us.s3.amazonaws.com/cache/99/4c/994c5997c7a509703cc53ec2000bb258.png', 'http://emojipedia-us.s3.amazonaws.com/cache/59/0c/590c832e73a472c416bf9d8bfdd02a4a.png'];
var imageShownIndex = 0;
var canvas = document.getElementById('image_canvas');
var canvasContext = canvas.getContext('2d');
function goToPreviousImage() {
imageShownIndex = (imageShownIndex==0) ? imageUrls.length-1 : imageShownIndex-1;
updateImage();
};
function goToNextImage() {
imageShownIndex = (imageShownIndex == imageUrls.length-1) ? 0 : imageShownIndex+1;
updateImage();
};
updateImage();
function updateImage() {
var img = new Image();
img.src = imageUrls[imageShownIndex];
canvasContext.clearRect(0, 0, 150, 150);
img.onload = function() {
canvasContext.drawImage(img, 0, 0);
}
}
</script>
</html>关于javascript - 使用上一个和下一个按钮在 javascript 中循环浏览图像，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43667450/