我正在尝试为用户上传的图片创建上传预览。我已经完成了大部分我想做的事情(多亏了 stackoverflow……大量的复制粘贴和一些调整)但是因为我不了解 JavaScript,所以我无法让它正常工作。
function uploadPreview(input) {
if (input.files && input.files[0]) {
var reader = new FileReader();
reader.onload = function(e) {
if (e.target.result.trim().length == 0) {
$('#serviceImage').attr('src', 'http://catawbabrewing.com/wp-content/themes/catawba/images/placeholder.png');
} else {
$('#serviceImage').attr('src', e.target.result);
}
}
reader.readAsDataURL(input.files[0]);
}
}
function uploadPreviewExt(input) {
if (input.trim().length == 0) {
var previewSrc = '{{CSS_URL}}/images/placeholder.jpg';
} else {
var previewSrc = input;
}
$('#serviceImage').attr('src', previewSrc);
}
function resetUploadPreview() {
if (!$('#previousImage').val()) {
$('#serviceImage').attr('src', 'http://catawbabrewing.com/wp-content/themes/catawba/images/placeholder.png');
} else {
$('#serviceImage').attr('src', '{{PROD_IMG}}/'.$('#previousImage').val());
}
}
$("#mainImage").change(function() {
uploadPreview(this);
});
$('[name="mainImgExt"]').on('change', function() {
uploadPreviewExt(this.value);
});
$('#clearUpload').on('click', function() {
$('#mainImage').val('');
if ($('#imgExt').val().trim().length == 0) {
resetUploadPreview();
} else {
uploadPreviewExt($('#imgExt').val());
}
});
$('#clearUploadExt').on('click', function() {
$('#imgExt').val('');
if (!$('#mainImage').val()) {
resetUploadPreview();
} else {
uploadPreview($('#mainImage'));
}
});
pointer {
cursor: pointer;
}
img.placeholder {
width: 100px;
height: 100px;
}
<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css">
<script src="//code.jquery.com/jquery-3.3.1.min.js"></script>
<script src="//unpkg.com/popper.js@1.12.9/dist/umd/popper.min.js"></script>
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<div class="form-group p-3 border p-2 rounded m-3">
<div class="row">
<div class="col-sm-3 text-center pt-2 border-right">
<label for="mainImage"><img src="http://catawbabrewing.com/wp-content/themes/catawba/images/placeholder.png" alt="Placeholder" id="serviceImage" class="placeholder img-thumbnail" aria-describedby="imagePreviewHelp" /></label>
<small id="imagePreviewHelp" class="form-text text-muted">Preview could appear stretched</small>
</div>
<div class="col">
<label for="mainImage">Image</label>
<div class="input-group mb-3">
<input type="file" class="form-control border p-1" id="mainImage" name="mainImage" />
<div class="input-group-append">
<span class="input-group-text bg-warning text-danger pointer" id="clearUpload">X</span>
</div>
</div>
<div class="input-group mb-3">
<input type="text" class="form-control" id="imgExt" name="mainImgExt" placeholder="Externel Image" aria-describedby="imageHelp" />
<div class="input-group-append">
<span class="input-group-text bg-warning text-danger pointer" id="clearUploadExt">X</span>
</div>
</div>
<small id="imageHelp" class="form-text text-muted">Upload a local image <strong>or</strong> link to an external image.</small>
</div>
</div>
</div>
涉及到很多 JavaScript(超出我的舒适区,因为我根本不知道)。
JavaScript 可以遇到两种 HTML 版本。这取决于用户是添加服务还是编辑服务。表单是在 TWIG 的帮助下动态生成的。
在JSFiddle中,有一个版本的表单的图片上传部分(如果是添加服务)下面是编辑服务的版本。 (添加了隐藏的输入字段“previousImage”,预览是当前图像而不是占位符)
<div class="form-group p-3 border p-2 rounded">
<div class="row">
<div class="col-sm-3 text-center pt-2 border-right">
<label for="mainImage"><img src="https://logismarketmx.cdnwm.com/ip/eve-maquinaria-mantenimiento-para-gruas-mantenimiento-de-gruas-987423-FGR.jpg" alt="Vinyl" id="serviceImage" class="placeholder img-thumbnail" aria-describedby="imagePreviewHelp" /></label>
<input type="hidden" name="previousImage" id="previousImage" value="eve-maquinaria-mantenimiento-para-gruas-mantenimiento-de-gruas-987423-FGR.jpg" />
<small id="imagePreviewHelp" class="form-text text-muted">Preview could appear stretched</small>
</div>
<div class="col">
<label for="mainImage">Image</label>
<div class="input-group mb-3">
<input type="file" class="form-control border p-1" id="mainImage" name="mainImage" />
<div class="input-group-append">
<span class="input-group-text bg-warning text-danger pointer" id="clearUpload">X</span>
</div>
</div>
<div class="input-group mb-3">
<input type="text" class="form-control" id="imgExt" name="mainImgExt" placeholder="Externel Image" aria-describedby="imageHelp" />
<div class="input-group-append">
<span class="input-group-text bg-warning text-danger pointer" id="clearUploadExt">X</span>
</div>
</div>
<small id="imageHelp" class="form-text text-muted">Upload a local image <strong>or</strong> link to an external image.</small>
</div>
</div>
</div>
这就是问题的背景。这就是我正在努力解决的问题。
当用户单击红色“X”以清除紧靠左侧的字段时,我需要它。它清除了该字段,但我还想重置上传预览图像。
第二个版本的表单之所以重要,是因为如果用户重置并添加,则图像会更改为占位符(本地上传会发生这种情况,但外部 URL 不会发生这种情况);但如果用户正在编辑一项服务,则上传预览将重置为之前为该服务设置的图像。
我有我认为应该可以工作的 javascript,但它没有。
function resetUploadPreview()
{
if(!$('#previousImage').val())
{
$('#serviceImage').attr('src', '{{CSS_URL}}/images/placeholder.jpg');
}
else
{
$('#serviceImage').attr('src', '{{PROD_IMG}}/' . $('#previousImage').val());
}
}
其背后的逻辑是,如果 ID 为“previousImage”的输入为空(或不存在),它将显示占位符,但如果它确实有值,我们将使用它的值(文件名)来显示此图像。
但它并没有这样做,清除本地文件上传会将图像重置为占位符,无论 previousImage 是否已填充,并且外部 url 根本不会清除。
我想实现的另一个功能是,如果两个字段都已填写(本地和外部),那么清除一个将在预览中显示另一个图像。
抱歉,如果这看起来很简单,逻辑对我来说似乎很简单,但我似乎无法让它工作,而且我不知道我错过了什么......在我看来一切都在它应该工作的地方,但是它只是没有。
编辑时它不会重置为之前的图像...它根本不会重置。控制台给我以下错误
TypeError: "../design/variant/productImages/".$ is not a function
它导致的代码行是:
function resetUploadPreview()
{
if(!$('#previousImage').val())
{
$('#serviceImage').attr('src', '{{CSS_URL}}/images/placeholder.jpg');
}
else
{
// This is the line that makes that error
$('#serviceImage').attr('src', '{{PROD_IMG}}/' . $('#previousImage').val());
}
}
添加新服务时,如果您先添加本地镜像,然后再添加外部图像,它会正常显示外部图像预览。但是一旦你清除外部图像,它应该显示本地镜像(因为它已被填充)但它根本不会改变预览。并且控制台没有显示任何警告/错误。
我做错了什么?
最佳答案
干得漂亮!
我做了两个调整:
在 JavaScript 中,string concatenation是通过使用
+
符号执行的,而不是.
符号。 (因此您引用了TypeError
消息。)我相应地更改了resetUploadPreview()
中的代码。uploadPreview()
函数不需要 jQuery 对象,但会传递一个 jQuery 对象以在清除外部图像字段时恢复主图像。我将其改为传递 DOM 元素:$('#mainImage')[0]
而不是$('#mainImage')
。有关详细信息,请参阅 What does $(selector)[0] mean in jQuery?
function uploadPreview(input) {
if (input.files && input.files[0]) {
var reader = new FileReader();
reader.onload = function(e) {
if (e.target.result.trim().length == 0) {
$('#serviceImage').attr('src', '//catawbabrewing.com/wp-content/themes/catawba/images/placeholder.png');
} else {
$('#serviceImage').attr('src', e.target.result);
}
}
reader.readAsDataURL(input.files[0]);
}
}
function uploadPreviewExt(input) {
if (input.trim().length == 0) {
var previewSrc = '{{CSS_URL}}/images/placeholder.jpg';
} else {
var previewSrc = input;
}
$('#serviceImage').attr('src', previewSrc);
}
function resetUploadPreview() {
if (!$('#previousImage').val()) {
$('#serviceImage').attr('src', 'http://catawbabrewing.com/wp-content/themes/catawba/images/placeholder.png');
} else {
$('#serviceImage').attr('src', '{{PROD_IMG}}/' + $('#previousImage').val());
}
}
$("#mainImage").change(function() {
uploadPreview(this);
});
$('[name="mainImgExt"]').on('change', function() {
uploadPreviewExt(this.value);
});
$('#clearUpload').on('click', function() {
$('#mainImage').val('');
if ($('#imgExt').val().trim().length == 0) {
resetUploadPreview();
} else {
uploadPreviewExt($('#imgExt').val());
}
});
$('#clearUploadExt').on('click', function() {
$('#imgExt').val('');
if (!$('#mainImage').val()) {
resetUploadPreview();
} else {
uploadPreview($('#mainImage')[0]);
}
});
pointer {
cursor: pointer;
}
img.placeholder {
width: 100px;
height: 100px;
}
<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css">
<script src="//code.jquery.com/jquery-3.3.1.min.js"></script>
<script src="//unpkg.com/popper.js@1.12.9/dist/umd/popper.min.js"></script>
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<div class="form-group p-3 border p-2 rounded m-3">
<div class="row">
<div class="col-sm-3 text-center pt-2 border-right">
<label for="mainImage"><img src="http://catawbabrewing.com/wp-content/themes/catawba/images/placeholder.png" alt="Placeholder" id="serviceImage" class="placeholder img-thumbnail" aria-describedby="imagePreviewHelp" /></label>
<small id="imagePreviewHelp" class="form-text text-muted">Preview could appear stretched</small>
</div>
<div class="col">
<label for="mainImage">Image</label>
<div class="input-group mb-3">
<input type="file" class="form-control border p-1" id="mainImage" name="mainImage" />
<div class="input-group-append">
<span class="input-group-text bg-warning text-danger pointer" id="clearUpload">X</span>
</div>
</div>
<div class="input-group mb-3">
<input type="text" class="form-control" id="imgExt" name="mainImgExt" placeholder="Externel Image" aria-describedby="imageHelp" />
<div class="input-group-append">
<span class="input-group-text bg-warning text-danger pointer" id="clearUploadExt">X</span>
</div>
</div>
<small id="imageHelp" class="form-text text-muted">Upload a local image <strong>or</strong> link to an external image.</small>
</div>
</div>
</div>
关于javascript - 使用重置默认值的 jQuery 上传图像预览,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/48591094/