Pass image from HTML via Android javascript interface

Question

My app loads a small HTML document that contains one image in a webview. How can I fetch this image and use it as a Bitmap object in my app?

I'm already using a JavaScriptInterface together with my webview for getting some other information, like passing booleans. Is it possible to pass an image aswell via the JavaScriptIterface? Is it a good idéa or is there a better way?

The problem is that i don't want to load the image one more time for specific reasons. Otherwise it would have been the obvious solution. I have loaded it once, and I want to re-use the image. — prograde
– prograde, Commented Mar 21, 2012 at 0:51

Community · Accepted Answer · 2017-05-23 12:24:12Z

2

Take a look at this question: Get image data in JavaScript?

You might be able to draw the image on a (I presume hidden) Canvas, then Base64-encode it with toDataURL and pass that as a string through the JS interface then decode it on the Java side. I imagine it'll be slow, but it's worth a try.

edited May 23, 2017 at 12:24

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answered Mar 21, 2012 at 1:02

kabuko

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4 Comments

prograde Over a year ago

Thanks! I tried this, but the JavaScript seems to crash when executing ctx.drawImage(img, 0, 0); I also need some advice on how to convert the string to a Bitmap object in the app.

prograde Over a year ago

Also, as I understand it, the toDataURL method works for png, might work for jpg, but not for gif. Is that correct?

kabuko Over a year ago

Unfortunately I can't say I've tried this so I can't help you too much with the details. It was just something that conceptually I thought might be helpful to you.

prograde Over a year ago

I solved the convert to Bitmap problem (If someone is interested: imageView.setImageBitmap(BitmapFactory.decodeByteArray(Base64.decodeBase64(imgString.getBytes(), 0, imageAsBytes.length)));). It works if I create an image in the Javascript, but it still crashes when I try the drawImage method.

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