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Android ADT Template Format Document
Wednesday, 16 October 2013

ADT Template Format


Status
Draft
Format Version
3
Last Updated
8/30/2012

Overview

This document describes the format and syntax for Android code templates. These templates provide starting points for entire projects (e.g. NewAndroidApplication) or application components such as activities (e.g. BlankActivity).

Although these templates were originally introduced in the ADT Plugin for Eclipse, the template format is designed for use by any IDE or command-line tool.

Templates are customizable. Each template exposes several options (called parameters) that allow developers to customize the generated code. The most common workflow for using a template is as follows:

  1. Choose a template.
  2. Populate template options (parameters).
  3. Preview and then execute the additions/changes to your project.

FreeMarker

Templates make heavy use of FreeMarker, a Java templating engine used to enable things like control flows and variable substitutions inside files. It's similar to PHP, Django templates, etc. For those more acquainted with C/C++, think of it as a preprocessor language (i.e. #ifdef).

By convention, any file in the template directory structure that is to be processed by FreeMarker should have the .ftl file extension. So if one of your source files is MyActivity.java, and it contains FreeMarker instructions, it should be named something like MyActivity.java.ftl.

For more documentation on FreeMarker, see the docs. In particular, the reference on string operations.

An example, templated version of an Android manifest, normally named AndroidManifest.xml.ftl is shown below.

<manifest xmlns:android="http://schemas.android.com/apk/res/android">
    <application>
        <activity android:name=".${activityClass}"
            android:label="@string/title_${activityToLayout(activityClass)}">
            <#if parentActivityClass != "">
            <meta-data android:name="android.support.PARENT_ACTIVITY"
                android:value="${parentActivityClass}" />
            </#if>
            <#if isLauncher>
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
            </#if>
        </activity>
    </application>
</manifest>

In this example excerpt from the BlankActivity template:

  • The expression ${activityClass} is bound to the value of the 'Activity Class' template parameter.
  • The expression ${activityToLayout(activityClass)} uses the activityToLayout method built into ADT to convert an activity class such as MyFooActivity to activity_my_foo.
  • The isLauncher boolean variable and parentActivityClass string varaibles are bound to the values of the 'Launcher Activity' and 'Hierarchical Parent' template parameter, respectively.

Directory Structure

A template is a directory containing a number of XML and FreeMarker files. The only two mandatory files are template.xml and recipe.xml.ftl. Template source files (PNG files, templated Java and XML files, etc.) belong in a root/ subdirectory. An example directory structure for a template is below:

  • MyTemplate/ — Root directory
    • template.xml — Metadata (description, parameters, etc.)
    • recipe.xml.ftl — Instructions/script (files to copy, etc.)
    • globals.xml.ftl — Optional global variables
    • template.png — Default template thumbnail
    • template_foo.png — Thumbnail when option 'foo' is selected
    • template_bar.png
    • root/ — Source files (which get processed/copied/merged with the output project)
      • AndroidManifest.xml.ftl
      • res/
      • src/
        • app_package/
          • MyActivity.java.ftl

More on the role of each of these files is discussed in the sections below.

template.xml

Each template directory must contain a template.xml file. This XML file contains metadata about the template, including the name, description, category and user-visible parameters that the IDE will present as options to the user. The XML file also indicates the name of the recipe XML file (which gets processed by FreeMarker), and the global variables XML file if there are global variables besides the template parameter values that should be visible to all FreeMarker-processed files (.ftl files).

An example template.xml is shown below.

<!-- A template for a blank activity. Use template format
     version 3, as described in this document. -->
<template
    format="3"
    revision="1"
    minApi="4"
    minBuildApi="11"
    name="New Blank Activity"
    description="Creates a new blank activity, with navigation.">
    <!-- Indicate that the Android Support Library (r8) should be
         added to the project, if it isn't already in the project. -->
    <dependency name="android-support-v4" revision="8" />
    <category value="Activities" />
    <!-- A string parameter; the value is available to FreeMarker
         processed files (.ftl files) as ${activityName}. -->
    <parameter
        id="activityName"
        name="Activity Name"
        type="string"
        constraints="class|unique|nonempty"
        suggest="${layoutToActivity(layoutName)}"
        default="MainActivity"
        help="The name of the activity class to create." />
    <parameter
        id="layoutName"
        name="Layout Name"
        type="string"
        constraints="layout|unique"
        suggest="${activityToLayout(activityClass)}"
        default="main"
        help="The name of the layout to create for the activity" />
    <parameter
        id="navType"
        name="Navigation Type"
        type="enum"
        default="none">
        <option id="none" default="true">None</option>
        <option id="tabs" minApi="11">Tabs</option>
        <option id="pager" minApi="11">Swipe Views</option>
        <option id="dropdown" minApi="11">Dropdown</option>
    </parameter>
    <!-- 512x512 PNG thumbnails. -->
    <thumbs>
        <!-- Default thumbnail. -->
        <thumb>template_default.png</thumb>
        <!-- Attributes act as selectors based on chosen parameters. -->
        <thumb navType="tabs">template_tabs.png</thumb>
        <thumb navType="dropdown">template_dropdown.png</thumb>
    </thumbs>
    <!-- Optional global variables. -->
    <globals file="globals.xml.ftl" />
    <!-- Required recipe (script) to run when instantiating
         the template. -->
    <execute file="recipe.xml.ftl" />
</template>

Below is a listing of supported tags in template.xml.

<template>

The template root element.

format
The template format version that this template adheres to. Should be 3.
revision
Optional. The version of this template (which you can increment when updating the template), as an integer.
name
The template's display name.
description
The template's description.
minApi
Optional. The minimum API level required for this template. The IDE will ensure that the target project has a minSdkVersion no lower than this value before instantiating the template.
minBuildApi
Optional. The minimum build target (expressed as an API level) required for this template. The IDE will ensure that the target project is targeting an API level greater than or equal to this value before instantiating the template. This ensures that the template can safely use newer APIs (optionally guarded by runtime API level checks) without introducing compile-time errors into the target project.

<dependency>

Indicates that the template requires that a given library be present in the target project. If not present, the IDE will add the dependency to the project.

name
The name of the library. Currently accepted values are:
  • android-support-v4
  • android-support-v13
revision
The minimum revision of the library required by this template.

<category>

The template type. This element is optional.

value
The template type. Should be one of the following values:
  • Applications
  • Activities
  • UI Components

<parameter>

Defines a user-customizable template parameter.

id
The identifier representing this variable, made available as a global variable in FreeMarker files. If the identifier is foo, the parameter value will be available in FreeMarker files as ${foo}.
name
The display name of the template parameter.
type
The data type of the parameter. Either string, boolean, enum, or separator.
constraints
Optional. Constraints to impose on the parameter's value. Constraints can be combined using |. Valid constraint types are:
  • nonempty — the value must not be empty
  • apilevel — the value should represent a numeric API level
  • package — the value should represent a valid Java package name
  • class — the value should represent a valid Java class name
  • activity — the value should represent a fully-qualified activity class name
  • layout — the value should represent a valid layout resource name
  • drawable — the value should represent a valid drawable resource name
  • string — the value should represent a valid string resource name
  • id — the value should represent a valid id resource name
  • unique — the value must be unique; this constraint only makes sense when other constraints are specified, such as layout, which would mean that the value should not represent an existing layout resource name
  • exists — the value must already exist; this constraint only makes sense when other constraints are specified, such as layout, which would mean that the value should represent an existing layout resource name
suggest
Optional. A FreeMarker expression representing the auto-suggested parameter value (a 'dynamic default'). When the user modifies other parameter values, and if this parameter's value has not been changed from its default, then the value changes to the result of this expression. This may seem to be circular since parameters can suggest against each other's values, but these expressions are only updated for non-edited values, so this approach lets the user edit either parameter value, and the other will automatically be updated to a reasonable default.
default
Optional. The default value for this parameter.
help
The help string to display to the user for this parameter.

<option>

For parameters of type enum, represents a choice for the value.

id
The parameter value to set if this option is chosen.
minApi
Optional. The minimum API level required if this option is chosen. The IDE will ensure that the target project has a minSdkVersion no lower than this value before instantiating the template.
[text]
The text content of this element represents the display value of the choice.

<thumb>

Represents a thumbnail for the template. <thumb> elements should be contained inside a <thumbs> element. The text contents of this element represent the path to the thumbnail. If this element has any attributes, they will be treated as selectors for parameter values. For example, if there are two thumbnails:

<thumbs>
  <thumb>template.png</thumb>
  <thumb navType="tabs">template_tabs.png</thumb>
</thumbs>

The template 'preview' thumbnail will show template_tabs.png if the value of the navType template parameter is tabs and template.png otherwise.

globals.xml.ftl

The optional globals XML file contains global variable definitions, for use in all FreeMarker processing jobs for this template.

An example globals.xml.ftl is shown below.

<globals>
    <global id="srcOut"
            value="src/${slashedPackageName(packageName)}" />
    <global id="activityNameLower"
            value="${activityName?lower_case}" />
    <global id="activityClass"
            value="${activityName}Activity" />
</globals>

recipe.xml.ftl

The recipe XML file contains the individual instructions that should be executed when generating code from this template. For example, you can copy certain files or directories (the copy instruction), optionally running the source files through FreeMarker (the instantiate instruction), and ask ADT to open a file in Eclipse after the code has been generated (the open instruction).

Note: The name of the recipe file is up to you, and is defined in template.xml. By convention, however, it's best to call it recipe.xml.ftl.

Note: The global variables in globals.xml.ftl are available for use in recipe.xml.ftl.

An example recipe.xml.ftl is shown below.

<recipe>
    <!-- runs FreeMarker, then copies from
         [template-directory]/root/ to [output-directory]. -->
    <instantiate from="AndroidManifest.xml.ftl" />
    <!-- automatically creates directories as needed -->
    <copy from="res/drawable-hdpi" />
    <copy from="res/drawable-mdpi" />
    <copy from="res/drawable-xhdpi" />
    <copy from="res/values/dimens.xml" />
    <copy from="res/values/styles.xml" />
    <copy from="res/values-large/dimens.xml" />
    <copy from="res/menu/main.xml"
            to="res/menu/${activityNameLower}.xml" />
    <instantiate from="res/values/strings.xml.ftl" />
    <!-- Decide which layout to add -->
    <#if navType?contains("pager")>
        <instantiate
            from="res/layout/activity_pager.xml.ftl"
              to="res/layout/activity_${activityNameLower}.xml" />
    <#elseif navType == "tabs" || navType == "dropdown">
        <copy from="res/layout/activity_fragment_container.xml"
                to="res/layout/activity_${activityNameLower}.xml" />
    <#else>
        <copy from="res/layout/activity_simple.xml"
                to="res/layout/activity_${activityNameLower}.xml" />
    </#if>
    <!-- Decide which activity code to add -->
    <#if navType == "none">
        <instantiate from="src/app_package/SimpleActivity.java.ftl"
                       to="${srcOut}/${activityClass}.java" />
    <#elseif navType == "pager">
        <instantiate from="src/app_package/PagerActivity.java.ftl"
                       to="${srcOut}/${activityClass}.java" />
    <#elseif navType == "tabs">
        <instantiate from="src/app_package/TabsActivity.java.ftl"
                       to="${srcOut}/${activityClass}.java" />
    <#elseif navType == "dropdown">
        <instantiate from="src/app_package/DropdownActivity.java.ftl"
                       to="${srcOut}/${activityClass}.java" />
    </#if>
    <!-- open the layout file when done -->
    <open file="res/layout/${activityNameLower}.xml" />
</recipe>

The instructions below are supported:

<copy>

The only required argument is from which specifies the location of the source files to copy under the root/ directory. All necessary ancestor directories are automatically created if needed.

The default destination location is the same path under the output directory root (i.e. the location of the destination project). If the optional to argument is provided, this specifies the output directory. Note that if the from path ends with .ftl, it will automatically be stripped. For example <instantiate from="res/values/strings.xml.ftl" /> is adequate; this will create a file named strings.xml, not strings.xml.ftl.

This argument works recursively, so if from is a directory, that directory is recursively copied.

<instantiate>

Same as <copy>, but each source file is first run through FreeMarker.

<merge>

This instruction will be used to merge the contents of a source file into an existing file in the project. The most common use case for this will be to add components to the AndroidManifest.xml file of the destination project, or to merge resources such as strings into an existing strings.xml file.

<open>

Instruct ADT to open the file created by the specified file argument in Eclipse after code generation is complete.

root/

The actual template files (resources, Java sources, Android Manifest changes) should be placed in the root/ directory, in a directory structure that roughly resembles what the output directory structure should look like.

One difference is that instead of placing source files in src/com/google/... you can just use a naming convention like src/app_package/ to indicate that files under this directory will be placed in the destination project's source file package root.

Extra Template Functions

Several functions are available to FreeMarker expressions and files beyond the standard set of built-in FreeMarker functions. These are listed below.

string activityToLayout(string)

This function converts an activity class-like identifer string, such as FooActivity, to a corresponding resource-friendly identifier string, such as activity_foo.

Arguments

activityClass
The activity class name, e.g. FooActivity to reformat.

See also

layoutToActivity

string camelCaseToUnderscore(string)

This function converts a camel-case identifer string, such as FooBar, to its corresponding underscore-separated identifier string, such as foo_bar.

Arguments

camelStr
The camel-case string, e.g. FooBar to convert to an underscore-delimited string.

See also

underscoreToCamelCase

string escapeXmlAttribute(string)

This function escapes a string, such as Android's such that it can be used as an XML attribute value: Android&apos;s. In particular, it will escape ', ", < and &.

Arguments

str
The string to be escaped.

See also

escapeXmlText

escapeXmlString

string escapeXmlText(string)

This function escapes a string, such as A & B's such that it can be used as XML text. This means it will escape < and >, but unlike escapeXmlAttribute it will not escape ' and ". In the preceeding example, it will escape the string to A &amp; B\s. Note that if you plan to use the XML text as the value for a <string> resource value, you should consider using escapeXmlString instead, since it performs additional escapes necessary for string resources.

Arguments

str
The string to escape to proper XML text.

See also

escapeXmlAttribute

escapeXmlString

string escapeXmlString(string)

This function escapes a string, such as A & B's such that it is suitable to be inserted in a string resource file as XML text, such as A &amp; B\s. In addition to escaping XML characters like < and &, it also performs additional Android specific escapes, such as escaping apostrophes with a backslash, and so on.

Arguments

str
The string, e.g. Activity's Title to escape to a proper resource XML value.

See also

escapeXmlAttribute

escapeXmlText

string extractLetters(string)

This function extracts all the letters from a string, effectively removing any punctuation and whitespace characters.

Arguments

str
The string to extract letters from

string classToResource(string)

This function converts an Android class name, such as FooActivity or FooFragment, to a corresponding resource-friendly identifier string, such as foo, stripping the 'Activity' or 'Fragment' suffix. Currently stripped suffixes are listed below.

  • Activity
  • Fragment
  • Provider
  • Service

Arguments

className
The class name, e.g. FooActivity to reformat as an underscore-delimited string with suffixes removed.

See also

activityToLayout

string layoutToActivity(string)

This function converts a resource-friendly identifer string, such as activity_foo, to a corresponding Java class-friendly identifier string, such as FooActivity.

Arguments

resourceName
The resource name, e.g. activity_foo to reformat.

See also

activityToLayout

string slashedPackageName(string)

This function converts a full Java package name to its corresponding directory path. For example, if the given argument is com.example.foo, the return value will be com/example/foo.

Arguments

packageName
The package name to reformat, e.g. com.example.foo.

string underscoreToCamelCase(string)

This function converts an underscore-delimited string, such as foo_bar, to its corresponding camel-case string, such as FooBar.

Arguments

underStr
The underscore-delimited string, e.g. foo_bar to convert to a camel-case string.

See also

camelCaseToUnderscore

Notes for Template Authors

Tools metadata

When creating activity layouts, make sure to include the activity name in the root view in the layout as part of the tools namespace, as shown in the following example:

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:text="@string/hello_world"
    android:padding="@dimen/padding_medium"
    tools:context=".${activityClass}" />

As of ADT 20 we use this attribute in layouts to maintain a mapping to the active activity to use for a layout. (Yes, there can be more than one, but this attribute is showing the activity context you want to edit the layout as. For example, it will be used to look up a theme registration (which is per-activity rather than per-layout) in the manifest file, and we will use this for other features in the future—for example to preview the action bar, which also requires us to know the activity context.

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