How to add a custom button state

Question

For instance, the default button has the following dependencies between its states and background images:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_window_focused="false" android:state_enabled="true"
        android:drawable="@drawable/btn_default_normal" />
    <item android:state_window_focused="false" android:state_enabled="false"
        android:drawable="@drawable/btn_default_normal_disable" />
    <item android:state_pressed="true" 
        android:drawable="@drawable/btn_default_pressed" />
    <item android:state_focused="true" android:state_enabled="true"
        android:drawable="@drawable/btn_default_selected" />
    <item android:state_enabled="true"
        android:drawable="@drawable/btn_default_normal" />
    <item android:state_focused="true"
        android:drawable="@drawable/btn_default_normal_disable_focused" />
    <item
        android:drawable="@drawable/btn_default_normal_disable" />
</selector>

How can I define my own custom state (smth like android:state_custom), so then I could use it to dynamically change my button visual appearance?

I was wanting extra states for an EditText view to determine when two password boxes match to show a little checkmark. — Nathan Schwermann
– Nathan Schwermann, Commented Dec 23, 2010 at 22:07

Neil Miller · Accepted Answer · 2012-11-16 16:11:17Z

297

The solution indicated by @(Ted Hopp) works, but needs a little correction: in the selector, the item states need an "app:" prefix, otherwise the inflater won't recognise the namespace correctly, and will fail silently; at least this is what happens to me.

Allow me to report here the whole solution, with some more details:

First, create file "res/values/attrs.xml":

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="food">
        <attr name="state_fried" format="boolean" />
        <attr name="state_baked" format="boolean" />
    </declare-styleable>
</resources>

Then define your custom class. For instance, it may be a class "FoodButton", derived from class "Button". You will have to implement a constructor; implement this one, which seems to be the one used by the inflater:

public FoodButton(Context context, AttributeSet attrs) {
    super(context, attrs);
}

On top of the derived class:

private static final int[] STATE_FRIED = {R.attr.state_fried};
private static final int[] STATE_BAKED = {R.attr.state_baked};

Also, your state variables:

private boolean mIsFried = false;
private boolean mIsBaked = false;

And a couple of setters:

public void setFried(boolean isFried) {mIsFried = isFried;}
public void setBaked(boolean isBaked) {mIsBaked = isBaked;}

Then override function "onCreateDrawableState":

@Override
protected int[] onCreateDrawableState(int extraSpace) {
    final int[] drawableState = super.onCreateDrawableState(extraSpace + 2);
    if (mIsFried) {
        mergeDrawableStates(drawableState, STATE_FRIED);
    }
    if (mIsBaked) {
        mergeDrawableStates(drawableState, STATE_BAKED);
    }
    return drawableState;
}

Finally, the most delicate piece of this puzzle; the selector defining the StateListDrawable that you will use as a background for your widget. This is file "res/drawable/food_button.xml":

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res/com.mydomain.mypackage">
<item
    app:state_baked="true"
    app:state_fried="false"
    android:drawable="@drawable/item_baked" />
<item
    app:state_baked="false"
    app:state_fried="true"
    android:drawable="@drawable/item_fried" />
<item
    app:state_baked="true"
    app:state_fried="true"
    android:drawable="@drawable/item_overcooked" />
<item
    app:state_baked="false"
    app:state_fried="false"
    android:drawable="@drawable/item_raw" />
</selector>

Notice the "app:" prefix, whereas with standard android states you would have used prefix "android:". The XML namespace is crucial for a correct interpretation by the inflater and depends on the type of project in which you are adding attributes. If it is an application, replace com.mydomain.mypackage with the actual package name of your application (application name excluded). If it is a library you must use "http://schemas.android.com/apk/res-auto" (and be using Tools R17 or later) or you will get runtime errors.

A couple of notes:

It seems you don't need to call the "refreshDrawableState" function, at least the solution works well as is, in my case
In order to use your custom class in a layout xml file, you will have to specify the fully qualified name (e.g. com.mydomain.mypackage.FoodButton)
You can as weel mix-up standard states (e.g. android:pressed, android:enabled, android:selected) with custom states, in order to represent more complicated state combinations

edited Nov 16, 2012 at 16:11

Neil Miller

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answered Apr 27, 2011 at 14:47

Giorgio Barchiesi

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17 Comments

Giorgio Barchiesi Over a year ago

Update: if the custom class derives from TextView, rather than Button, the call to refreshDrawableState appears to be necessary, otherwise the widget appearance is not updated. The call shall be placed in the setters. I have not tried other classes. Tests performed on a froyo device.

buergi Over a year ago

The refreshDrawableState is definitely important. I'm not absolutely sure when it's really needed. But in my case it was needed when setting the state programmatically. I guess it is possibly called from the View class automatically in the onTouchEvent. I'd better add it in the setSelected method.

Peterdk Over a year ago

But how can you use custom states that are not boolean? Or are selectors only operating on booleans?

kAmol Over a year ago

How does it work? I mean, how the attribute gets updated to state true/false? Who updates it? Does merging drawablestate, only if local variable is true, updates the state or value of attribute? Which code exactly will be updating R.attr.state_fried?

Artyom Over a year ago

It seems that now we may use xmlns:app="http://schemas.android.com/apk/res-auto" everywhere, not only in libraries. stackoverflow.com/a/30620868/6182136

|

Ted Hopp · Accepted Answer · 2010-12-21 02:49:56Z

10

This thread shows how to add custom states to buttons and the like. (If you can't see the new Google groups in your browser, there's a copy of the thread here.)

answered Dec 21, 2010 at 2:49

Ted Hopp

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7 Comments

Vit Khudenko Over a year ago

+1 thanks a lot, Ted! Right now origin of the trouble has gone so I did not get to the actual implementation. However should my customer return to this again I will try the way you pointed me to.

Nathan Schwermann Over a year ago

Looks exactly like what I need, however the state-list drawables for my custom states aren't changing I must be missing something...

Ted Hopp Over a year ago

Are you calling refreshDrawableState()?

Mitch Over a year ago

The links are dead.

Ted Hopp Over a year ago

@Mitch -- Well, that's too bad. I'll see if I can find some replacement links. If not, I'll delete this answer, as it's basically useless as is. Meanwhile, the accepted answer has all the info needed.

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GabrielOshiro · Accepted Answer · 2016-05-30 21:03:45Z

8

Please do not forget to call refreshDrawableState within UI thread:

mHandler.post(new Runnable() {
    @Override
    public void run() {
        refreshDrawableState();
    }
});

It took lot of my time to figure out why my button is not changing its state even though everything looks right.

edited May 30, 2016 at 21:03

GabrielOshiro

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answered Jul 25, 2014 at 17:44

Nishant Soni

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1 Comment

Arthur Melo Over a year ago

where or when should I post this handler?

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