A customizable selector that replicates the behaviour of a knob with discrete values.


The knob is a powerful tool. For some reason, anyway, it's rarely used, and I could not find it in the Android panorama. But the rotating knob has a lot of advantages over other radio-buttons, seek bars or other selectors:

• It's usage is immediately clear to the user, because it also exists in the physical world
• It has an immediate graphical indication of the current value, the number of choices and where the value is in the overall range
• It docks in a very small space: it requires the same space no matter how many choices are there, and it can adapt itself when the amount changes. Furthermore, swipe gestures allow to change values very quickly, using the entire screen for the gesture, but only a tiny zone of it for the graphics.
• Works fine also with few choices, as a multi-state toggle.
  
  Possible usages are:
• Replacement for a radio button, with 2 up to dozen of choices
• Replacement for a integer value input or seek bar, with large ranges up to hundreds
• Replacement for a ViewPager indicator, for fast scrolling pages without using an entire line of the screen

This version is still in beta and still misses a number of features that are going to be added in the next future.

In your project's build.gradle file:

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

In your Application's or Module's build.gradle file:

dependencies {
    ...
    compile 'com.github.BeppiMenozzi:Knob:1.9.0'
    ...
}

Layout:

...
xmlns:app="http://schemas.android.com/apk/res-auto"
...
<it.beppi.knoblibrary.Knob
        android:layout_width="64dp"
        android:layout_height="64dp"
        android:id="@+id/knob"
        app:kNumberOfStates="6"
 />

Listener:

...
Knob knob = (Knob) findViewById(R.id.knob);
knob.setState(firstState);
knob.setOnStateChanged(new Knob.OnStateChanged() {
        @Override
        public void onState(int state) {
        // do something
        }
    });

...

The Knob is completely customizable. The many customizable attributes can all be set both via xml file, and programmatically.

Let's analyze the structure to understand how it is drawn before digging into the customization. The knob is made of these parts:

• A circle that represents the knob. The knob does not necessarily occupy the entire size of the view, but can be slightly smaller to leave space for, for example, the markers.
• A set of markers that represent the available values. The markers are lines drawn from the edge of the largest possible circle inside the view towards the center. Therefore, they can lie outside or inside the knob. One of the markers is "selected" and can have its own color.
• An indicator that represents the current value. The indicator is a line drawn from the knob circle edge towards the center. To the indicator a spring animation is applied.
• A circular indicator that works exactly like the normal indicator, but is a drawn as a circle. The two ndicators can live alone or together.
• A circle that represents the knob center.
• An empty circle that represents the knob border.
  
  

Here is the list of the xml attributes that can be used to customize the View. All these attributes are available programmatically too with the same names.

You don't have to add any dependency. Internally, this library uses my other Balloon Popup library to display... guess... balloon popups.

• Added 'user' click behaviour

• Fixed: default swipe direction (thanks for pull request)
• Added different onClick behaviours, included the somewhere asked popup menu

• Added public constants for swipe direction

• Added swipe in circular fashion
• Changed the default swipe behaviour to circular

• Fixed: when min and max angles were present, the last marker was not in the correct place
• Added swipe in both directions
• Fixed: balloon now does not exit the window
• minSdkVersion from 9 to 11

• Fixed swipe behaviour while in ScrollView.

• Added popup balloons

• Debug

• Added samples

• Added continuous mode

• Added constrained rotation
• Added min / max angle
• Added accented markers
• Added drawables
• Rewritten angle management (and rotation direction)

• Debug

• Added swipe gestures
• Added methods increaseValue() decreaseValue()
• Fixed small things.

• Allow to put multiple indicators

• BalloonPopup doesn't scroll when inside a ScrollView

• Beppi Menozzi

The MIT License (MIT)

Copyright (c) 2016 Beppi Menozzi

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

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SOFTWARE.