How to Download the file which is uploaded locally - sapui5

Question

I was going through the samples of Upload Collections :
Sample from Docs
Here I tried uploading a PDF file which has uploaded and shown as :
On selection Download enables and saw the code for download is as:
onDownloadItem: function() {
var oUploadCollection = this.byId("UploadCollection");
var aSelectedItems = oUploadCollection.getSelectedItems();
if (aSelectedItems) {
for (var i = 0; i < aSelectedItems.length; i++) {
oUploadCollection.downloadItem(aSelectedItems[i], true);
}
} else {
MessageToast.show("Select an item to download");
}
},
It doesn't download any , but when i tried downloading other preexisting files, downloads successfully.
May I know why the local uploaded files doesn't download ?
Does the uploaded files needed any extra attributes ? as the existing one's have few such as:
"documentId" : "64469d2f-b3c4-a517-20d6-f91ebf85b9da",
"fileName" : "Screenshot.jpg",
"mimeType" : "image/jpg",
"thumbnailUrl" : "",
"url" : "test-resources/sap/m/demokit/sample/UploadCollection/LinkedDocuments/Screenshot.jpg",.....
But when uploaded a new these all are empty in the code:
"documentId": jQuery.now().toString(), // generate Id,
"fileName": sUploadedFile,
"mimeType": "",
"thumbnailUrl": "",
"url": "".......
I am clueless on how to download files uploaded locally , any guiding links are much appreciated ...TIA
+1 Q --> May I How generally are uploaded files saved to DB ?
I have gone through docs but couldn't find any solution , but read and found a similar one to download but no luck :
sap.ui.core.util.File.save();

Answer 1

When link is pressed, get base64 with a FileReader
var file = event.getSource().getParent().getFileObject();
var reader = new FileReader();
// call for file content
reader.readAsDataURL(file);
reader.onload = function (e) {
var base64 = e.target.result;
}
Then create a Blob from base64 and open it as an iFrame:
var blobUrl = URL.createObjectURL(blob);
var myWindow = window.open("");
myWindow.document.write("<iframe width='100%' height='100%' src='" + blobUrl + "'></iframe>");
myWindow.document.close();
But if you don't want to just open it in a new window you can download it as soon as you have a file content.