Android - custom UI with custom attributes

Question

I know it is possible to create custom UI element (by way of View or specific UI element extension). But is it possible to define new properties or attributes to newly created UI elements (I mean not inherited, but brand new to define some specific behavior I am not able to handle with default propertis or attributes)

e.g. element my custom element:

<com.tryout.myCustomElement
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="Element..."
   android:myCustomValue=<someValue>
/>

So is it possible to define MyCustomValue?

Thx

Hey here you have some nice article about the custom attributes in android - amcmobileware.org/android/blog/2016/09/11/custom-attributes — Arkadiusz Cieśliński
– Arkadiusz Cieśliński, Commented Nov 15, 2016 at 19:46

danronmoon · Accepted Answer · 2023-02-15 15:01:47Z

264

Yes. Short guide:

Create an attribute XML

Create a new XML file inside /res/values/attrs.xml, with the attribute and its type

<?xml version="1.0" encoding="UTF-8"?>
<resources>
    <declare-styleable name="MyCustomElement">
        <attr name="distanceExample" format="dimension"/>
    </declare-styleable>
</resources>

Basically you have to set up one <declare-styleable /> for your view that contains all your custom attributes (here just one). I never found a full list of possible types, so you need to look at the source for one I guess. Types that I know are reference (to another resource), color, boolean, dimension, float, integer and string. They are pretty self-explanatory

Use the attributes in your layout

That works the same way you did above, with one exception. Your custom attribute needs its own XML namespace.

<com.example.yourpackage.MyCustomElement
   xmlns:customNS="http://schemas.android.com/apk/res/com.example.yourpackage"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="Element..."
   customNS:distanceExample="12dp"
   />

Pretty straight forward.

Make use of the values you get passed

Modify the constructor of your custom view to parse the values.

public MyCustomElement(Context context, AttributeSet attrs) {
    super(context, attrs);
        
    TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.MyCustomElement, 0, 0);
    try {
        distanceExample = ta.getDimension(R.styleable.MyCustomElement_distanceExample, 100.0f);
    } finally {
        ta.recycle();
    }
    // ...
}

distanceExample is a private member variable in this example. TypedArray has lots of other things to parse other types of values.

And that's it. Use the parsed value in your View to modify it, e.g. use it in onDraw() to change the look accordingly.

edited Feb 15, 2023 at 15:01

danronmoon

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answered Sep 30, 2011 at 9:57

user658042

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10 Comments

zskalnik Over a year ago

Just note about TypedArray. Be sure to call recycle() when done with them.

yahya Over a year ago

Here you can find a good list github.com/android/platform_frameworks_base/blob/master/core/…

AlikElzin-kilaka Over a year ago

Does the IDE (eclipse for example) auto-complete the keys/values of custom attributes?

Dori Over a year ago

for gradle builds you should use http://schemas.android.com/apk/res-auto when declaring the custom namespace

kosiara - Bartosz Kosarzycki Over a year ago

In step 3, you can simply use String initialText = attrs.getAttributeValue("http://schemas.android.com/apk/res-auto", "initialText"); where attr is the AttributeSet that is passed in the constructor and 'initialText' is your custom attribute name

|

Maria Neumayer · Accepted Answer · 2011-09-30 09:55:31Z

22

In your res/values folder create attr.xml. There you can define your attribues:

<declare-styleable name="">
    <attr name="myCustomValue" format="integer/boolean/whatever" />
</declare-styleable>

When you then want to use it in your layout file you have to add

xmlns:customname="http://schemas.android.com/apk/res/your.package.name"

and then you can use the value with customname:myCustomValue=""

answered Sep 30, 2011 at 9:55

Maria Neumayer

3,3573 gold badges31 silver badges44 bronze badges

1 Comment

Fazal Over a year ago

this is not the answer, the question is how to programatically change from java

Frank Cheng · Accepted Answer · 2011-09-30 09:42:18Z

-14

Yes , you can.Just use <resource> tag.
like this:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <style name="CodeFont" parent="@android:style/TextAppearance.Medium">
        <item name="android:layout_width">fill_parent</item>
        <item name="android:layout_height">wrap_content</item>
        <item name="android:textColor">#00FF00</item>
        <item name="android:typeface">monospace</item>
    </style>
</resources>

link from official website

answered Sep 30, 2011 at 9:42

Frank Cheng

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1 Comment

Waypoint Over a year ago

Thanks for answer. But in resource, i see using default "android:" values. My point is, can I have e.g. android:phoneNameSelected="true" as a parameter of my custom UI element?

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