Preview image in client by JavaScript when upload image in multi-browsers

郎宏逸

2023-12-01

how to preview image in client by JavaScript when upload image in multi-browsers. It works well in IE6/IE7/IE8/FireFox3.*/Safari4/Chrome3.

I think it is worth to you, please take a look.

Attached is the demo project.

As you know in IE6 you can use JavaScript code like this “document.getElementById(‘previewImgId’).src = document.getElementById(‘inputFileId’).value;” to preview the local image, but it can’t support all browsers, because in new version of Firefox/Safari/ Chrome you can only get the file name not the full path and for the security concern JavaScript is forbidden to access local resource.

The solution is:

For Firefox

use JavaScript function “getAsDataURL()” to get data from URL.

For IE

1. Use the value of input file control with the condition that JavaScript can get full image path in some version.

2. Use filter to show image preview.

For safari/chrome:

Use jQuery plug-in ajaxFileUpload.

Use server to handle image preview by Ajax simulate submission.

With below steps:

1. Clone the input file control, change the original input control id and name.

2. Create a form control, add the original control into this form, set the action to image preview handler.

3. Create a iframe.

4. Submit the created form to the created iframe.

5. Handle the request file, write the thumbnail image stream into context response.

6. Use callback function to got the return stream to show the handled image.

7. Move the original input file control back, remove the cloned control, set back the id and name to keep constraint.

This step is very important, in original plug-in, it only can preview image but can’t submit in Safari/Chrome, because the cloned input file control can’t keep the user file selection.

It makes the preview feature can support all common browsers.

8. Remove the form and iframe.

Code:

imagePreview.js:

return false;
}

ajaxFileUpload.js:
jQuery.extend({

    createUploadIframe: function(frameId, uri) {
        //create frame
        if (window.ActiveXObject) {
            var io = document.createElement('<iframe id="' + frameId + '" name="' + frameId + '" />');
            if (typeof uri == 'boolean') {
                io.src = 'javascript:false';
            }
            else if (typeof uri == 'string') {
                io.src = uri;
            }
        }
        else {
            var io = document.createElement('iframe');
            io.id = frameId;
            io.name = frameId;
        }
        io.style.position = 'absolute';
        io.style.top = '-1000px';
        io.style.left = '-1000px';

document.body.appendChild(io);

return io
},

    createUploadForm: function(fileId, fileElementId, formId) {
        //create form
        var form = $('<form action="" method="POST" name="' + formId + '" id="' + formId + '" enctype="multipart/form-data"></form>');
        var oldElement = $('#' + fileElementId);
        var newElement = $(oldElement).clone();
        $(oldElement).attr('id', fileId);
        $(oldElement).attr('name', fileId);
        $(oldElement).before(newElement);
        $(oldElement).appendTo(form);
        //set attributes
        $(form).css('position', 'absolute');
        $(form).css('top', '-1200px');
        $(form).css('left', '-1200px');
        $(form).appendTo('body');
        return form;
    },

    ajaxFileUpload: function(s) {
        // TODO introduce global settings, allowing the client to modify them for all requests, not only timeout
        s = jQuery.extend({}, jQuery.ajaxSettings, s);
        var id = new Date().getTime()
        var fileId = 'jUploadFile' + id;
        var frameId = 'jUploadFrame' + id;
        var formId = 'jUploadForm' + id;
        var form = jQuery.createUploadForm(fileId, s.fileElementId, formId);
        var io = jQuery.createUploadIframe(frameId, s.secureuri, frameId);
        // Watch for a new set of requests
        if (s.global && !jQuery.active++) {
            jQuery.event.trigger("ajaxStart");
        }
        var requestDone = false;
        // Create the request object
        var xml = {}
        if (s.global)
            jQuery.event.trigger("ajaxSend", [xml, s]);
        // Wait for a response to come back
        var uploadCallback = function(isTimeout) {
            var io = document.getElementById(frameId);
            try {
                if (io.contentWindow) {
                    xml.responseText = io.contentWindow.document.body ? io.contentWindow.document.body.innerHTML : null;
                    xml.responseXML = io.contentWindow.document.XMLDocument ? io.contentWindow.document.XMLDocument : io.contentWindow.document;

                } else if (io.contentDocument) {
                    xml.responseText = io.contentDocument.document.body ? io.contentDocument.document.body.innerHTML : null;
                    xml.responseXML = io.contentDocument.document.XMLDocument ? io.contentDocument.document.XMLDocument : io.contentDocument.document;
                }
            } catch (e) {
                jQuery.handleError(s, xml, null, e);
            }
            if (xml || isTimeout == "timeout") {
                requestDone = true;
                var status;
                try {
                    status = isTimeout != "timeout" ? "success" : "error";
                    // Make sure that the request was successful or notmodified
                    if (status != "error") {
                        // process the data (runs the xml through httpData regardless of callback)
                        var data = jQuery.uploadHttpData(xml, s.dataType);
                        // If a local callback was specified, fire it and pass it the data
                        if (s.success)
                            s.success(data, status);

                        // Fire the global callback
                        if (s.global)
                            jQuery.event.trigger("ajaxSuccess", [xml, s]);
                    } else
                        jQuery.handleError(s, xml, status);
                } catch (e) {
                    status = "error";
                    jQuery.handleError(s, xml, status, e);
                }

                // The request was completed
                if (s.global)
                    jQuery.event.trigger("ajaxComplete", [xml, s]);

                // Handle the global AJAX counter
                if (s.global && ! --jQuery.active)
                    jQuery.event.trigger("ajaxStop");

                // Process result
                if (s.complete)
                    s.complete(xml, status);

jQuery(io).unbind()

                setTimeout(function() {
                    try {
                        //Must move the original input file control back, because the cloned input file control will not keep the file.
                        var oldElement = $('#' + s.fileElementId);
                        var oldName = $(oldElement).attr('name');
                        var newElement = $('#' + fileId);
                        $(oldElement).before(newElement);
                        $(oldElement).remove();
                        $(newElement).attr('id', s.fileElementId);
                        $(newElement).attr('name', oldName);

$(io).remove();
$(form).remove();

                    } catch (e) {
                        jQuery.handleError(s, xml, null, e);
                    }

}, 100)

                xml = null
            }
        }
        // Timeout checker
        if (s.timeout > 0) {
            setTimeout(function() {
                // Check to see if the request is still happening
                if (!requestDone) uploadCallback("timeout");
            }, s.timeout);
        }
        try {
            // var io = $('#' + frameId);
            var form = $('#' + formId);
            $(form).attr('action', s.url);
            $(form).attr('method', 'POST');
            $(form).attr('target', frameId);
            if (form.encoding) {
                form.encoding = 'multipart/form-data';
            }
            else {
                form.enctype = 'multipart/form-data';
            }
            $(form).submit();

        } catch (e) {
            jQuery.handleError(s, xml, null, e);
        }
        if (window.attachEvent) {
            document.getElementById(frameId).attachEvent('onload', uploadCallback);
        }
        else {
            document.getElementById(frameId).addEventListener('load', uploadCallback, false);
        }
        return { abort: function() { } };

    uploadHttpData: function(r, type) {
        var data = !type;
        data = type == "xml" || data ? r.responseXML : r.responseText;
        // If the type is "script", eval it in global context
        if (type == "script")
            jQuery.globalEval(data);
        // Get the JavaScript object, if JSON is used.
        if (type == "json")
            eval("data = " + data);
        // evaluate scripts within html
        if (type == "html")
            jQuery("<div>").html(data).evalScripts();
        //alert($('param', data).each(function(){alert($(this).attr('value'));}));
        return data;
    }
})

Handler.cs:

public class PreviewHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        HttpFileCollection files = context.Request.Files;
        string title = string.Empty;

        if (files.Count > 0)
        {
            for (int i = 0; i < files.Count; i++)
            {
                HttpPostedFile file = files[i];

                if (file.ContentLength > 0)
                {
                    if (GetValidFileTypeList().Contains(Path.GetExtension(file.FileName).ToLower()))
                    {
                        MemoryStream previewImage = ImageHelper.ClipImage(file.InputStream, 100, 100);
                        context.Response.Write("{ error:'', msg: '', data: '" + Convert.ToBase64String(previewImage.ToArray()) + "' }");
                    }
                }
            }
        }
        else
        {
            context.Response.Write("{error:'Unexpected error.', msg:'No file uploaded.'}");
        }
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }

    private List<string> GetValidFileTypeList()
    {
        return new List<string>(new string[] { ".jpg", ".bmp", ".gif", ".jpeg", ".png", ".tif", ".tiff" });
    }
}

Default.aspx:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Preview Solution in multi-browser when upload image </title>

Preview image in client by JavaScript when upload image in multi-browsers

相关阅读

相关文章

相关问答