在html / js windows universal app 8.1中通过后台传输上传之前调整图像大小 [英] resize image before upload via background transfer in html/js windows universal app 8.1

问题描述

我想调整从手机图库中挑选的图片，然后通过后台传输上传它到目前为止我有： -

   filePicker  。  pickSingleFileAsync  （）。 然后 （  function    （  file  ）    {  
 uploadSingleFileAsync  （  uri  ，  file  ）;   
  }）。 完成 （  null  ，  displayException  ）;   
 
   function   uploadSingleFileAsync  （  uri  ，  file  ）    {  
   if    （！  file  < span class ="pun"style ="margin：0px; padding：0px; border：0px; vertical-align：baseline; color：＃000000; background：transparent">）    {  
 displayError  （ "错误：未选择文件。"  ）;   
   return  ;   
  }   
   return  文件 。  getBasicPropertiesAsync  （）。 然后 （  function    （  properties  ）    {  
   if    （  properties  。  size  >   maxUploadFileSize  ）     {  
 displayError  （ "所选文件超过最大上传文件大小（"    +    （  maxUploadFileSize   /    （  1024     *     1024  ））    +   
  " MB）。"  ）;   
   return  ;   
  }   
   var  上传  =     new     UploadOperation  （）;   
   //尝试这个压缩文件，但它不起作用，显然不适合该对象  
   // file = file.slice（0，Math.round（file.size / 2））;   
上传 。  start  （  uri  ，  file  ）;   
   //在全局数组中保持上传操作。  
 uploadOperations  。  push  （  upload  ）;   
  }）;   
  }   

然后其余部分上传文件。我尝试添加.slice但它不起作用（我猜测因为文件是一个对象而不是）而且我不知道如何压缩这种类型的文件对象。我似乎无法在msdn或windows
dev论坛上找到任何示例或建议，我可以在服务器上显然重新调整照片，但我宁愿用户不是他们的文件上传时间比他们要长的时间要长。我非常希望能够调整音频和视频文件的大小，如果可能的话......

我需要保存图像才能操作吗？任何建议都会非常感谢！

解决方案

您可以使用BitmapEncoder以较小的尺寸重新编码位图.S ee如何编辑图像（HTML）
的基础知识。

I would like to resize an image picked from the gallery of the phone before uploading it via background transfer so far I have:-

filePicker.pickSingleFileAsync().then(function (file) {
                            uploadSingleFileAsync(uri, file);
                        }).done(null, displayException);

function uploadSingleFileAsync(uri, file) {
                    if (!file) {
                        displayError("Error: No file selected.");
                        return;
                    }
                    return file.getBasicPropertiesAsync().then(function (properties) {
                        if (properties.size > maxUploadFileSize) {
                            displayError("Selected file exceeds max. upload file size (" + (maxUploadFileSize / (1024 * 1024)) +
                                " MB).");
                            return;
                        }
                        var upload = new UploadOperation();
                        //tried this to compress the file but it doesnt work obviously not right for the object
                        //file = file.slice(0, Math.round(file.size / 2));
                        upload.start(uri, file);
                        // Persist the upload operation in the global array.
                        uploadOperations.push(upload);
                    });
                }

and the rest then uploads the file. I tried adding in .slice but it doesn't work (im guessing because file is an object rather than) and I'm not sure how to compress this type of file object. I can't seem to find any examples or advice on msdn or the windows dev forums, I can obviously resize the photos once they are on the server but I would rather users are not waiting longer than they have to for their files to upload. I would quite like to be able to resize audio and video files as well if that is at all possible...

Do I need to save the image before I can manipulate it? Any advice would be greatly appreciated!

解决方案

You can use a BitmapEncoder to reencode the bitmap at a smaller size. See How to edit an image (HTML) for the basics.

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