Why is .NET core HTTP post clearing my byte array

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I have a problem with a .NET Core HTTP Post clearing my byte array.

I can choose an image, and capture it in the controller, save it to the database then retrieve render it successfully the next time the form is loaded.

Then the fun starts. If I click save on the form without changing anything an examine the class that the form Model is base on as soon as the controller tagged with [HttpPost] is opened everything on the class is unchanged as expected except for my byte array and ImageMimeType Properties

They have both been blanked. Any ideas why this might be?

public Byte[] p_Photo
{
    get
    {
        return m_Photo;
    }
    set
    {
        m_Photo = value;
        m_FlagSettings = m_FlagSettings | m_FlagBits.PHOTO;
    }

}
[Column("ImageMimeType")]
public string p_ImageMimeType {
    get
    {
        return m_ImageMimeType;
    }
    set
    {
        m_ImageMimeType = value;
    }
}
protected string m_ImageMimeType;
protected Byte[] m_Photo;

What I have tried:

Lots of searching on line and also a workaround in javascript to take the rendered image and pass it back to the Html Element. No joy so far.

Posted 24-Oct-18 7:53am

Ger Hayden

Updated 24-Oct-18 8:54am

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Richard Deeming · Accepted Answer · 2018-10-24T08:55:00

You'll need a hidden field with a name that matches the property you're trying to persist.

For the MIME type, that's simple:

@Html.HiddenFor(m => m.p_ImageMimeType)

For the image bytes, it's not quite as simple, since byte arrays aren't supported by default. You could write a custom model binder; but it's probably simpler to use a separate property:

C#

public string p_PhotoData
{
    get { return m_Photo == null ? null : Convert.ToBase64String(m_Photo); }
    set { m_Photo = string.IsNullOrEmpty(value) ? null : Convert.FromBase64String(value); }
}

@Html.HiddenFor(m => m.p_PhotoData)