我希望能够在上传文件(图像)之前预览它。预览操作应该在浏览器中全部执行,而不使用Ajax上传图像。
我该怎么做?
我希望能够在上传文件(图像)之前预览它。预览操作应该在浏览器中全部执行,而不使用Ajax上传图像。
我该怎么做?
当前回答
对于我的应用程序,使用加密的GET url参数,只有这一点有效。我总是得到一个TypeError:$(…)为空。摘自https://developer.mozilla.org/en-US/docs/Web/API/FileReader/readAsDataURL
函数previewFile(){var preview=document.querySelector('img');var file=document.querySelector('input[type=file]').files[0];var reader=新文件读取器();reader.addEventListener(“load”,函数(){preview.src=读取结果;},假);if(文件){reader.readAsDataURL(文件);}}<input-type=“file”onchange=“previewFile()”><br><img src=“”height=“200”alt=“图像预览…”>
其他回答
对这是可能的。
Html
<input type="file" accept="image/*" onchange="showMyImage(this)" />
<br/>
<img id="thumbnil" style="width:20%; margin-top:10px;" src="" alt="image"/>
JS
function showMyImage(fileInput) {
var files = fileInput.files;
for (var i = 0; i < files.length; i++) {
var file = files[i];
var imageType = /image.*/;
if (!file.type.match(imageType)) {
continue;
}
var img=document.getElementById("thumbnil");
img.file = file;
var reader = new FileReader();
reader.onload = (function(aImg) {
return function(e) {
aImg.src = e.target.result;
};
})(img);
reader.readAsDataURL(file);
}
}
您可以从这里获得现场演示。
这里有一种在上传前使用纯javascript预览图像的简单方法;
//profile_change is the id of the input field where we choose an image
document.getElementById("profile_change").addEventListener("change", function() {
//Here we select the first file among the selected files.
const file = this.files[0];
/*here i used a label for the input field which is an image and this image will
represent the photo selected and profile_label is the id of this label */
const profile_label = document.getElementById("profile_label");
//Here we check if a file is selected
if(file) {
//Here we bring in the FileReader which reads the file info.
const reader = new FileReader();
/*After reader loads we change the src attribute of the label to the url of the
new image selected*/
reader.addEventListener("load", function() {
dp_label.setAttribute("src", this.result);
})
/*Here we are reading the file as a url i.e, we try to get the location of the
file to set that as the src of the label which we did above*/
reader.readAsDataURL(file);
}else {
//Here we simply set the src as default, whatever you want if no file is selected.
dp_label.setAttribute("src", "as_you_want")
}
});
这里是HTML;
<label for="profile_change">
<img title="Change Profile Photo" id="profile_label"
src="as_you_want" alt="DP" style="height: 150px; width: 150px;
border-radius: 50%;" >
</label>
<input style="display: none;" id="profile_change" name="DP" type="file" class="detail form-control">
对于我的应用程序,使用加密的GET url参数,只有这一点有效。我总是得到一个TypeError:$(…)为空。摘自https://developer.mozilla.org/en-US/docs/Web/API/FileReader/readAsDataURL
函数previewFile(){var preview=document.querySelector('img');var file=document.querySelector('input[type=file]').files[0];var reader=新文件读取器();reader.addEventListener(“load”,函数(){preview.src=读取结果;},假);if(文件){reader.readAsDataURL(文件);}}<input-type=“file”onchange=“previewFile()”><br><img src=“”height=“200”alt=“图像预览…”>
在React中,如果文件在你的props中,你可以使用:
{props.value instanceof File && (
<img src={URL.createObjectURL(props.value)}/>
)}
我编辑了@Ivan的答案,以显示“无预览可用”图像,如果它不是图像:
function readURL(input) {
var url = input.value;
var ext = url.substring(url.lastIndexOf('.') + 1).toLowerCase();
if (input.files && input.files[0]&& (ext == "gif" || ext == "png" || ext == "jpeg" || ext == "jpg")) {
var reader = new FileReader();
reader.onload = function (e) {
$('.imagepreview').attr('src', e.target.result);
}
reader.readAsDataURL(input.files[0]);
}else{
$('.imagepreview').attr('src', '/assets/no_preview.png');
}
}