Setting attributes of custom views in Android

Question

I've got a class that extends a button. I want to add an additional attribute to it. Is there any way to initialize that attribute from XML? For example:

<MyButton android:id="@+id/myBtn" myValue="Hello World"></MyButton>

public class MyButton extends Button{
private String myValue = "";

public CalcButton(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}
}

Community · Accepted Answer · 2017-05-23 12:27:46Z

1

Yes. You can have custom attributes and assign values to it in XML. You can even assign methods to handle custom events on your widgets. Long press definition at XML layout, like android:onClick does

The needed steps.

Implement your custom widget.

Then add file attrs.xml in res/values/ with following content:

<xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="MyButton">
        <attr name="myValue" format="string"/>
    </declare-styleable>
</resources>

Retrieve values from XML in MyButton constructor. Remember to implement all constructors, not only one.

Use new attribute in your layout xml:

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/res/**your.package**"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    >

    <your.package.MyButton
        android:id="@+id/theId"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        custom:myValue="myDoSomething"
    />
    <!-- Other stuff -->
</LinearLayout>

edited May 23, 2017 at 12:27

CommunityBot

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answered Nov 28, 2012 at 8:24

Aleksander Gralak

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2 Comments

Yevgeny Simkin Over a year ago

how do you actually fetch custom:myValue within the MyButton class?

Aleksander Gralak Over a year ago

@GeniaS. please look at the link I have provided. There is a full code example with retreiving valuse from xml in constructor.

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