CODEWITHSUNDEEP
androidandroid-layout
Arturs Vancans
Arturs Vancans

Reputation: 4640

Difference between android: and app: prefix in Android XML?

What is the difference and more importantly the necessity of having different prefixes in Andriod view XML?

For example,

<android.support.v7.widget.Toolbar
    android:id="@+id/actionToolBar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:contentInsetEnd="20dp"
    app:contentInsetEnd="20dp"
    android:elevation="3dp"
  />

Has contentInsetEnd for both android and app.

Upvotes: 50

Views: 15118

Answers (3)

Bojan Kseneman
Bojan Kseneman

Reputation: 15668

app namespace is used for custom defined attributes, which are usually defined in /values/attrs.xml Here is a sample of such file

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="SimpleTabIndicator">
        <attr name="numberOfTabs" format="integer"/>
        <attr name="indicatorColor" format="color"/>
    </declare-styleable>
</resources>

And a sample usage would be

<com.someapp.demo.SimpleTabIndicator
    android:id="@+id/tabIndicator"
    android:layout_width="match_parent"
    android:layout_height="2dp"
    android:background="#26292E"
    app:indicatorColor="#FFFDE992"
    app:numberOfTabs="5"/>

Android namespace you use for Android's widgets and UI controls.

Upvotes: 15

Ga&#235;tan
Ga&#235;tan

Reputation: 12552

android is usually used for attribute coming from Android SDK itself.

app is often used if you are using the support library.

You may also see other namespaces if you are using custom views (of your own or form a library).

Here is some extra information: http://developer.android.com/training/custom-views/create-view.html#customattr

Upvotes: 49

inmyth
inmyth

Reputation: 9050

app is just a namespace for any custom parameters for a custom View.

This can be anything but if you see the root element there's probably a line xmlns:app="http://schemas.android.com/apk/res-auto" that assigns the namespace .

Upvotes: 11

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