Develop Reference

Xamarin forms: Image Cache

Hi I am trying to build an app using xamarin forms PCL. I am implementing image gallery in which I have used a default image. All the images are on blob. I want to download image and cache that Image in device and as soon as download is complete I need to replace my default image with it.
And on loading app next time download image only if it is not present in cache.
I dont get any plugin for image caching and loading image from cache.
I have seen a plugin named FFPLUGIN but it didnt work.
Any idea how I can implement this? IMAGE CACHING

You could use the built in ImageCaching in Xamarin Forms shown here:
https://developer.xamarin.com/guides/xamarin-forms/working-with/images/#Downloaded_Image_Caching
Downloaded Image Caching
UriImageSource also supports caching of
downloaded images, configured through the following properties:
CachingEnabled - Whether caching is enabled ( true by default).
CacheValidity - A TimeSpan that defines how long the image will be
stored locally. Caching is enabled by default and will store the image
locally for 24 hours. To disable caching for a particular image,
instantiate the image source like this:
Image.Source = new UriImageSource {CachingEnabled = false,
Uri="http://server.com/image"}; To set a specific cache period (for
example, 5 days) instantiate the image source like this:
webImage.Source = new UriImageSource {
Uri = new Uri("https://xamarin.com/content/images/pages/forms/example-app.png"),
CachingEnabled = true,
CacheValidity = new TimeSpan(5,0,0,0) };
Built-in caching makes it very easy to support scenarios like scrolling lists of images, where
you can set (or bind) an image in each cell and let the built-in cache
take care of re-loading the image when the cell is scrolled back into
view.

Displaying image that was previously uploaded to server

For a project I'm working I would like the user (admin) to be able to change the picture on the page he is currently on. I managed to upload the image to "the server" using interlink. This basicly uploads it to a given folder on a server, in my case being: Interlink/Uploads.
But now I don't really know how can I tell my website to replace the source of the image that is currently shown with the source of the uploaded image.
Another something I would like to do is create a simple image gallery with all the images in that folder, once again I don't know how to do this.
I hope somebody can help me, Thanks.
Thomas
Edit: Just so clarify, the application is written in silverlight (XAML, C#). I apologise for any inconvenience.

I take it that the "Silverlight" portion of this question is related only to Interlink (your file uploader), and not to the page itself, which I presume is straight HTML.
If that's the case, you've got several options for changing the local image. The simplest way is simply to wait until you know that your file upload has finished (presumably Interlink has some way of notifying you that this is the case), and then run something like this bit of JavaScript:
<script type='text/javascript'>
function changeImage(newImageSource) {
document.getElementById('myTargetImage').setAttribute('src', newImageSource);
}
</script>
As far as displaying a simple image gallery with all the images in the folder, my recommendation would be to look into one of the numerous jquery plugins that handle this sort of thing, e.g.:
http://www.1stwebdesigner.com/css/fresh-jquery-image-gallery-display-solutions/
EDIT: Silverlight Options
You basically have the same options, except you're doing them in C# instead of JavaScript. For instance, when Interlink tells you that the new image has been uploaded, run this:
string imageName = "something.jpeg";
var ub = new UriBuilder(HtmlPage.Document.DocumentUri);
ub.Path = "/Interlink/Uploads/" + imageName;
img.Source = new BitmapImage(ub.Uri);
And for an image carousel, something like this:
http://3dimagecarousel.codeplex.com/
You'll just need to provide the URL's of all the images. The easiest way to do that is probably to expose a web service method that lists them all.

Image not loading correctly from BitmapImage in code behind

Okay, I'm attempting to load an image to an Image control on my page. Now as far as I know, I know how to do this (the method I'm using has worked before). But for some reason it's not working this time. The image is not being loaded.
Okay, let's start with the XAML. You can see it here.. Please note my excellent artistic skills. You can see that the top image is the left one on the screen and the bottom image is the right one. As you can also see, the image on the right is loaded in the XAML from a file in the Assets/Images folder. It should also be noted that we can take from this that the image loads okay - there aren't errors with the image. We can also see that the images are not blocked by anything (when the program runs, the right image shows just fine).
So the left image, 'image1' is the one that I'm loading from the code behind. Here is the code behind for that page. As you can see, there's not a lot. Yes I do use a view model, but it doesn't interface with the image at all (its only exposed properties are an Entity (for a selected item) and an ObservableCollection of entities (for the ItemsSource of a control)). As you can also see, I'm attempting to load the same image as is used for the static image (so I can say for sure that the image is okay for Silverlight).
If you're wondering about the BitmapCreateOptions line, that was something that someone suggested to me to add. I have tried removing it, but that doesn't seem to cause any difference.
The next question is - have I attempted to use the event handler for the failure? Yes I have. The error I get is 'AG_E_NETWORK_ERROR'.
I'm not sure what exactly this is about - I'm not loading from a network.
Can anyone offer assistance? Thanks.

I can't help but notice that in your XAML, you have a "../" at the start of the image path, but this is missing from the path you're using in code-behind. Could this be the problem?

Have You tried to call BeginInit and EndInit before and after setting the uri?
BitmapImage bmpImg = new BitmagImage();
bmpImg.BeginInit();
bmpImg.UriSource = new Uri(...);
bmpImg.EndInit();
Or use the constructor that takes an Uri. msdn

how to resize a picture programatically and add it to the web site

Hi there
I am working with visual web developer and would a) like to know how I could programatcally add a picture to the website, instead of going to Website and then add existing item. The idea I have is to upload the picture using the file upload control but then I want to have it added so that it can be accessed using a gridview.
b)I would also like to know how to size the picture using C# code obviously so that is displayed at the correct size.
best regards
arian

here is a full project with source code to manipulate images, including resize.
http://www.codeproject.com/KB/web-image/ASPImaging1.aspx
And a sample code only for resize
http://weblogs.asp.net/gunnarpeipman/archive/2009/04/02/resizing-images-without-loss-of-quality.aspx

You can use GetThumbnailImage to easily create a smaller verson of the uploaded image. The code looks something like (it's free typed without a compiler, so there may be some errors):
System.Drawing.Image pic = new System.Drawing.Bitmap(sourceFilename);
System.Drawing.Image thumb = pic.GetThumbnailImage(targetXSize,targetYSize,
new System.Drawing.Image.GetThumbnailImageAbort(this.GetThumbnailImageAbort),
IntPtr.Zero);
thumb.Save(thumbPathName);
I believe the Image implements IDisposable, so you need to remember to Dispose of them when you're done.
The abort parameter can be a function that simply does this (can't remember off the top of my head when it gets called):
bool GetThumbnailImageAbort() {
return false;
}

Render HTML as an Image

I'm generating a coupon based on dynamic input and a cropped image, and I'm displaying the coupon using ntml and css right now, the problem is, printing this has become an issue because of how backgrounds disappear when printing and other problems, so I think the best solution would be to be able to generate an image based on the html, or set up some kind of template that takes in strings and an image, and generates an image using the image fed in as a background and puts the coupon information on top.
Is there anything that does this already?
This is for an ASP.NET 3.5 C# website!
Thanks in advance.
edit: It'd be great if the output could be based on the HTML input, as the coupon is designed by manipulating the DOM using jQuery and dragging stuff around, it all works fine, it's just when it comes to the printing (to paper) it has z-indexing issues.

What you can do is create an aspx page that changes the response type to be in the format you want and then put the image into the stream. I created a barcode generator that does a similar thing. Excluding all the formalities of generating the image, you'll Page_Load will look something like this:
Bitmap FinalBitmap = new Bitmap();
MemoryStream msStream = new MemoryStream();
strInputParameter == Request.Params("MagicParm").ToString()
// Magic code goes here to generate your bitmap image.
FinalBitmap.Save(msStream, ImageFormat.Png);
Response.Clear();
Response.ContentType = "image/png";
msStream.WriteTo(Response.OutputStream);
if ((FinalBitmap != null)) FinalBitmap.Dispose();
and that's it! Then all you have to do in your image is set the URL to be something like RenderImage.aspx?MagicParm=WooHoo or whatever you need. That way you can have it render whatever you want to specify.

You can render html to a bitmap using the WebBrowser control in either a winforms or console application.
An example of this can be found here: http://www.wincustomize.com/articles.aspx?aid=136426&c=1
The above example can be modified to run in ASP.Net by creating a new STAThread and performing an Application.Run on it to start a new message loop.

PHP/Ruby Alternative
If you have accessed this question and are actually looking for soething that will work without Windows, you can try the KHTML library: http://wiki.goatpr0n.de/projects/khtmld
The website has a ridiculous name I admit, but I can assure you it is genuine. Other related pages are: the sourceforge page http://khtml2png.sourceforge.net/

Try PDFSharp...it's not exactly a "take this HTML and make a PDF" but with a small amout of fiddling you can easily make a PDF out of the info you are using to make the HTML.

MARKUP ONLY ALTERNATE SOLUTION
Use SVG and XSLT to transform the html data into an image that can be rendered/saved/etc.
I'll admit that at first it was tedious getting this to work because of all of the coordinates, but well worth the effort once it is running.

There is a very powerful image creation library called GD which I often use with PHP.
I am led to believe there is a wrapper for this library that ASP programmers can use. Try this

Unless the "other problems" are pretty severe, couldn't you just instruct your users to turn on Background Images when printing?
In any case, I'd default to serving a PDF rather than an image, doubly so since it is intended for print.

Just set up your css properly, so that you have a css file targeted at the print medium. It is pretty easy to guarantee that the coupon will always be legible, without worrying about whether they have bg images on or not. Needlesly moving to an image doesn't make any sense, unless there is some reason you don't want it to be machine readable.

I haven't tried to myself, but you should be able to render HTML into an image by using the WebBrowser control and the DrawToBitmap() method inherited from the base Control class.
UPDATE: I tried this myself and there are some caveats. The WebBrowser control doesn't seem to render the web page until the control is show, so the WebBrowser needs to be in a Form and the Form must be shown for the HTML to be rendered and the DocumentCompleted event to be raised.