MvvmCross Android Bind Image from byte[]

问题:

Does anyone know how to bind a byte[] (image) to a Image control in a axml view. My ViewModel inherit from MvxViewModel. All my other bindings works great but I cannot find a way to bind that image.

回答1:

I think you could bind this using a custom UI control.

To do this, you'll need to do something like:

1. inherit a new MyImageView from ImageView
2. add the default constructor (which passes the context and attributes down to the base constructor)

3. add a new RawImage property to MyImageView, implementing it as:

   private byte[] _rawImage;
   public byte[] RawImage
   {
        get { return _rawImage; }
        set 
        {
                _rawImage = value;
                if (_rawImage == null)
                        return;
   
                var bitmap = BitmapFactory.DecodeByteArray(_rawImage, 0,_rawImage.Length);
                SetImageBitmap(bitmap);
        }
   }
   

You can then use that MyImageView control in your axml instead of the normal ImageView.

Note - this code above not tested - but once you get the byte[] in the View I'm sure you'll work out what Droid code to use.

---

As an alternative approach to this, you could also use a custom binding to bind a byte[] to a normal ImageView - see an example of custom binding in In MvvmCross how do I do custom bind properties

回答2:

You can do it even easier and I also found that out after stumbling on that question:

As the Android-binding for setting a Bitmap for a ImageView is Bitmap (as you can see at [1]), you can configure your view like this:

    <ImageView
        local:MvxBind="Bitmap ByteArrayToImage(ImageByteArray)" />

Then you only need to define a ValueConverter, called ByteArrayToImageValueConverter, that converts the byte array to an instance of Bitmap. For me, using a ValueConverter is the preferred way over creating custom binding ;)

You already had the code for converting a byte array to a bitmap: BitmapFactory.DecodeByteArray(_rawImage, 0,_rawImage.Length);

[1] https://github.com/MvvmCross/MvvmCross/blob/bbf9a2ac76e74d9404f4b57036c6e29dfe2cc6c3/Cirrious/Cirrious.MvvmCross.Binding.Droid/MvxAndroidBindingBuilder.cs#L79