A seekbar, in form of a fully customizable rotating knob selector with discrete values for Android. Replaces radio buttons, seekbars, integer value inputs, progress bars and even ViewPager indicators.
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README.md

Rotary Knob Selector

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.

Setup

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'
    ...
}

Minimal usage

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
        }
    });

...

As default, nearly all features are disabled and the default knob is minimal:


This is what you will have with this default configuration. Feel free to grab graphics and configurations from the sample as you like to match your own needs.

Some other fancy configurations that you can find in the sample:


Graphical structure

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.

Customization

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.

General
kNumberOfStatesNumber of possible states. States are numbered from 0 to n-1. This number can be changed runtime, and the indicator will adjust its position accordingly.
kDefaultStateThe starting state of the knob.
kClickBehaviourWhat is expected when the knob is clicked. Next value, previous value, reset to default value, let the user select with a popup menu, define a custom listener. Default is next. Warning: the popup menu is available only with Compat. Warning: the customer listener (a Runnable) should be defined runtime, with setUserBehaviour()
kAnimationEnable / disable indicator's animation.
kAnimationSpeedParameter "speed" applied to the spring physical model for the indicator's animation.
kAnimationBouncinessParameter "bounciness" applied to the spring physical model for the indicator's animation.
kEnabledEnable / disable knob.
Knob appearance
kKnobColorColor of the knob.
kKnobRelativeRadiusRadius of the knob, relative to the largest possible circle inside the view. 1 = fill all the view, 0.5 = fill half of the view.
kKnobCenterColorColor of the center of the knob.
kKnobCenterRelativeRadiusRadius of the center, relative to the radius of the knob. 0 = disable.
kBorderWidthWidth of the external circle. 0 = disable.
kBorderColorColor of the external circle.
kKnobDrawableAllows to override a color configuration and set a drawable as the knob graphics. If this is present, both kKnob* and kKnobCenter* attributes will be ignored.
kKnobDrawableRotatesWhen this is true, the drawable will be rotated accordingly, otherwise it will stay still.
State markers appearance
kStateMarkersWidthWidth of the line markers.
kStateMarkersRelativeLengthLength of the line markers, relative to the largest possible circle inside the view. 1 = draw from edge to center, 0.5 = draw half length, starting from the edge.
kStateMarkersColorColor of the line markers.
kSelectedStateMarkerColorColor of the selected line marker.
kSelectedStateMarkerContinuousIf the continuous mode is chosen, the knob will act like a gauge, selecting all the markes from the minimum to the current value. When this is false, only one marker is selected at any time.
kStateMarkersAccentWidthThese attributes allow to create different "more important" markers, like on a normal clock are the minutes divisible by 5
kStateMarkersAccentColor
kStateMarkersAccentRelativeLength
kStateMarkersAccentPeriodicityHow often these markers are shown. 0 = disable.
Indicators appearance
kIndicatorWidthWidth of the line indicator. 0 = disable.
kIndicatorColorColor of the line indicator.
kIndicatorRelativeLengthLength of the line indicator relative to the knob radius. 1 = from edge to center. 0.5 = from edge to half. 0 = disable.
kCircularIndicatorRelativeRadiusRadius of the circle indicator, relative to the knob radius. 0 = disable.
kCircularIndicatorRelativePositionDistance of the circle indicator from the center, relative to the largest possible circle inside the view. 1 = put on edge, 0.5 = put half way.
kCircularIndicatorColorColor of the circular indicator.
Swipe behaviour
kSwipeEnable swipe. Values: off, vertical, horizontal, both or circular (default: circular).
kSwipeSensitivityPixelsHow many pixels are needed for the swipe to make the knob increase value. Higher = slower (default: 100). If the circular swipe gesture is chosen, this parameter is ignored.
Rotation and constraints
kFreeRotationEnable free rotation. When false, after reaching maximum or minimum the indicator will stop, when true the value will continue in a round-robin fashion. Default: true
kMinAnglePut constraints on the indicator. This allows to create indicators that span only one arc, and don't cover the entire circumference, like, for example, a speedometer. If this and the next parameters are set, generally they go together with kFreeRotation=off
kMaxAngle
Popup balloons
kShowBalloonValuesEnable popup balloon values
kBalloonValuesTimeToLiveHow long do the popup balloons display. 0 = permanent
kBalloonValuesRelativePositionRelative position of the balloons. 0 = center, 1 = edge. Values >1 are allowed
kBalloonValuesTextSizeBalloon's text size
kBalloonValuesAnimationAnimation. Choose among *fade*, *pop* or *scale*
kBalloonValuesArrayArray of strings for the balloon values. If this is not defined, numbers will be written
kBalloonValuesSlightlyTransparentWhen true, the balloons will be 75% visibile

Dependencies

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

New in 1.9.0

  • Added 'user' click behaviour

New in 1.8.0

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

New in 1.7.0

  • Added public constants for swipe direction

New in 1.6.0

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

New in 1.5.0

  • 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

New in 1.4.0

  • Fixed swipe behaviour while in ScrollView.

New in 1.3.0

  • Added popup balloons

New in 1.2.3

  • Debug

New in 1.2.2

  • Added samples

New in 1.2.1

  • Added continuous mode

New in 1.2.0

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

New in 1.1.1

  • Debug

New in 1.1.0

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

TODO List

  • Allow to put multiple indicators

Known bugs

  • BalloonPopup doesn't scroll when inside a ScrollView

Author

  • Beppi Menozzi

License

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.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.