ScalingImageView

An ImageView that transforms its drawable according to touch input.

Supports rotated images and keeps transformation when you exchange the image for another one with a different size.

All of that in ~400 lines of code (excluding blanks and comments).

How to include

Gradle

Add the JitPack repository in your root build.gradle at the end of repositories:

allprojects {
	repositories {
		...
		maven { url 'https://jitpack.io' }
	}
}

Then add the dependency in your app/build.gradle:

dependencies {
	implementation 'com.github.markusfisch:ScalingImageView:1.2.0'
}

Android Archive

Alternatively you may just download the latest aar from Releases and put it into app/libs in your app.

Then make sure your app/build.gradle contains the following line in the dependencies block:

dependencies {
	implementation fileTree(dir: 'libs', include: '*')
	...
}

How to use

Maybe in a layout:

<de.markusfisch.android.scalingimageview.widget.ScalingImageView
	android:layout_width="match_parent"
	android:layout_height="match_parent"
	android:src="@drawable/your_drawable"/>

Or from java:

import de.markusfisch.android.scalingimageview.widget.ScalingImageView;

ScalingImageView scalingImageView = new ScalingImageView(context);

Changing the scale type must happen in source since reading attributes would require a declare-styleable resource and some overhead I think would outweigh its value for this.

So you need to call setScaleType():

scalingImageView.setScaleType(ImageView.ScaleType.CENTER_CROP);

Only CENTER, CENTER_CROP and CENTER_INSIDE are supported. CENTER_INSIDE is the default.

Please note that using android:adjustViewBounds="true" will implicitly set ScaleType to FIT_CENTER what is not supported and will result in an UnsupportedOperationException.

Supported Scale Types

ImageView.ScaleType.CENTER

Center the image in the view, but perform no scaling.

    +-------+ FRAME
    |       |
  +-|-------|-+
  | | IMAGE | |
  +-|-------|-+
    |       |
    +-------+

ImageView.ScaleType.CENTER_CROP

Scale the image uniformly (maintain the image's aspect ratio) so that both dimensions (width and height) of the image will be equal to or larger than the corresponding dimension of the view.

      FRAME
+---+-------+---+
|   |       |   |
|   |       |   |
| I |M  A  G| E |
|   |       |   |
|   |       |   |
+---+-------+---+

ImageView.ScaleType.CENTER_INSIDE

Scale the image uniformly (maintain the image's aspect ratio) so that both dimensions (width and height) of the image will be equal to or less than the corresponding dimension of the view.

    +-------+ FRAME
    |       |
    +-------+
    | IMAGE |
    +-------+
    |       |
    +-------+

Image Rotation

You can either set any image rotation (in degrees) at any time with setImageRotation():

scalingImageView.setImageRotation(90f);

Or allow the user to freely rotate the image with setFreeRotation():

scalingImageView.setFreeRotation(true);

If you want to know the angle and pivot of the rotation, you can use getImageRotation(), getPivotX() and getPivotY(). Just make sure to always invoke getImageRotation() first as it also updates the pivot point.

Demo

In app/ you'll find a demo. Either import it into Android Studio or, if you're not on that thing from Redmond, just type make to build, install and run.

License

This widget is so basic, it should be Public Domain. And it is.