android_frameworks_base/docs/html/guide/topics/text/creating-input-method.jd

page.title=Creating an Input Method
parent.title=Articles
parent.link=../browser.html?tag=article
@jd:body

<div id="qv-wrapper">
<div id="qv">
<h2>See also</h2>
<ol>
    <li>
        <a href="http://android-developers.blogspot.com/2009/04/updating-applications-for-on-screen.html">Onscreen Input Methods</a>
    </li>
    <li>
        <a href="{@docRoot}resources/samples/SoftKeyboard/index.html">Soft Keyboard sample</a>
    </li>
</ol>
</div>
</div>
<p>
    An input method editor (IME) is a user control that enables users to enter text. Android 
    provides an extensible input method framework that allows applications to provide users 
    alternative input methods, such as on-screen keyboards or even speech input. Once installed, 
    users can select which IME they want to use from the system settings and use it across the 
    entire system; only one IME may be enabled at a time.
</p>
<p>
    To add an IME to the Android system, you create an Android application
    containing a class that extends {@link android.inputmethodservice.InputMethodService}. In 
    addition, you usually create a "settings" activity that passes options to the IME
    service. You can also define a settings UI that's displayed as part of the system settings.
</p>
<p>This article covers the following:</p>
<ul>
    <li>The IME lifecycle.</li>
    <li>Declaring IME components in the application manifest.</li>
    <li>The IME API.</li>
    <li>Designing an IME UI.</li>
    <li>Sending text from an IME to an application.</li>
    <li>Working with IME subtypes.</li>
</ul>
<p>
    If you haven't worked with IMEs before, you should read the introductory article 
    <a href="http://android-developers.blogspot.com/2009/04/updating-applications-for-on-screen.html">Onscreen Input Methods</a> first.
    Also, the Soft Keyboard sample app included in the SDK contains sample code that you can modify
    to start building your own IME.
</p>
<h2 id="InputMethodLifecycle">The IME Lifecycle</h2>
<p>
    The following diagram describes the life cycle of an IME:
</p>
<img src="{@docRoot}resources/articles/images/inputmethod_lifecycle_image.png" alt="" height="845"
    id="figure1" />
<p class="img-caption">
    <strong>Figure 1.</strong> The life cycle of an IME.
</p>
<p>
    The following sections describe how to implement the UI and code associated with an IME that
    follows this lifecycle.
</p>
<h2 id="DefiningIME">Declaring IME Components in the Manifest</h2>
<p>
    In the Android system, an IME is an Android application that contains a special IME service.
    The application's manifest file must declare the service, request the necessary permissions, 
    provide an intent filter that matches the action <code>action.view.InputMethod</code>, and 
    provide metadata that defines characteristics of the IME. In addition, to provide a settings
    interface that allows the user to modify the behavior of the IME, you can define a "settings"
    activity that can be launched from System Settings.
</p>
<p>
    The following snippet declares IME service. It requests the permission {@link
    android.Manifest.permission#BIND_INPUT_METHOD} to allow the service to connect the IME to 
    the system, sets up an intent filter that matches the action 
    <code>android.view.InputMethod</code>, and defines metadata for the IME:
</p>
<pre>
&lt;!-- Declares the input method service --&gt;
    &lt;service android:name="FastInputIME"
        android:label="&#64;string/fast_input_label"
        android:permission="android.permission.BIND_INPUT_METHOD"&gt;
        &lt;intent-filter&gt;
            &lt;action android:name="android.view.InputMethod" /&gt;
        &lt;/intent-filter&gt;
        &lt;meta-data android:name="android.view.im" android:resource="&#64;xml/method" /&gt;
    &lt;/service&gt;
</pre>
<p>
    This next snippet declares the settings activity for the IME. It has an intent filter for
    {@link android.content.Intent#ACTION_MAIN} that indicates this activity is the main entry point
    for the IME application:</p>
<pre>
    &lt;!-- Optional: an activity for controlling the IME settings --&gt;
    &lt;activity android:name="FastInputIMESettings" 
        android:label="&#64;string/fast_input_settings"&gt;
        &lt;intent-filter&gt;
            &lt;action android:name="android.intent.action.MAIN"/&gt;
        &lt;/intent-filter&gt;
    &lt;/activity&gt;
</pre>
<p>
    You can also provide access to the IME's settings directly from its UI.
</p>
<h2 id="IMEAPI">The Input Method API</h2>
<p>
    Classes specific to IMEs are found in the {@link android.inputmethodservice} and {@link
    android.view.inputmethod} packages. The {@link android.view.KeyEvent} class is important for
    handling keyboard characters.
</p>
<p>
    The central part of an IME is a service component, a class that extends 
    {@link android.inputmethodservice.InputMethodService}. In addition to implementing the 
    normal service lifecycle, this class has callbacks for providing your IME's UI, handling user 
    input, and delivering text to the field that currently has focus. By default, the
    {@link android.inputmethodservice.InputMethodService} class provides most of the implementation 
    for managing the state and visibility of the IME and communicating with the current 
    input field.
</p>
<p>
    The following classes are also important:
</p>
<dl>
    <dt>{@link android.view.inputmethod.BaseInputConnection}</dt>
    <dd>
        Defines the communication channel from an {@link android.view.inputmethod.InputMethod}
        back to the application that is receiving its input. You use it to read text around the
        cursor, commit text to the text box, and send raw key events to the application.
        Applications should extend this class rather than implementing the base interface 
        {@link android.view.inputmethod.InputConnection}.
    </dd>
    <dt>{@link android.inputmethodservice.KeyboardView}</dt>
    <dd>
        An extension of {@link android.view.View} that renders a keyboard and responds to user
        input events. The keyboard layout is specified by an instance of 
        {@link android.inputmethodservice.Keyboard}, which you can define in an XML file.
    </dd>
</dl>
<h2 id="IMEUI">Designing the Input Method UI</h2>
<p>
    There are two main visual elements for an IME: the <strong>input</strong> view and the
    <strong>candidates</strong> view. You only have to implement the elements that are relevant to
    the input method you're designing.
</p>
<h3 id="InputView">Input view</h3>
<p>
    The input view is the UI where the user inputs text, in the form of keyclicks, handwriting or
    gestures. When the iIME is displayed for the first time, the system calls the 
    {@link android.inputmethodservice.InputMethodService#onCreateInputView()} callback. In your
    implementation of this method, you create the layout you want to display in the IME
    window and return the layout to the system. This snippet is an example of implementing the
    {@link android.inputmethodservice.InputMethodService#onCreateInputView()} method:
<pre>
    &#64;Override 
    public View onCreateInputView() { 
        MyKeyboardView inputView = 
            (MyKeyboardView) getLayoutInflater().inflate( R.layout.input, null);
    
        inputView.setOnKeyboardActionListener(this); inputView.setKeyboard(mLatinKeyboard); 
        
        return mInputView; 
    } 
</pre>
<p>
    In this example, {@code MyKeyboardView} is an instance of a custom implementation of 
    {@link android.inputmethodservice.KeyboardView} that renders a 
    {@link android.inputmethodservice.Keyboard}. If you’re building a traditional QWERTY keyboard, 
    see the <a href=”{@docRoot}resources/samples/SoftKeyboard/index.html”>Soft Keyboard</a> sample 
    app for an example of how to extend the {@link android.inputmethodservice.KeyboardView} class.
</p>
<h3 id="CandidateView">Candidates view</h3>
<p>
    The candidates view is the UI where the IME displays potential word corrections or
    suggestions for the user to select. In the IME lifecycle, the system calls 
    {@link android.inputmethodservice.InputMethodService#onCreateCandidatesView()} when it's ready 
    to display the candidate view. In your implementation of this method, return a layout that shows
    word suggestions, or return null if you don’t want to show anything (a null response is the
    default behavior, so you don’t have to implement this if you don’t provide suggestions).</p>
<p>
    For an example implementation that provides user suggestions, see the 
    <a href=”{@docRoot}resources/samples/SoftKeyboard/index.html”>Soft Keyboard</a> sample app.
</p>
<h3 id="DesignConsiderations">UI design considerations</h3>
<p>
    This section describes some specific UI design considerations for IMEs.
</p>
<h4>Handling multiple screen sizes</h4>
<p>
    The UI for your IME must be able to scale for different screen sizes, and it also
    must handle both landscape and portrait orientations. In non-fullscreen IME mode, leave
    sufficient space for the application to show the text field and any associated context, so that
    no more than half the screen is occupied by the IME. In fullscreen IME mode this is not an
    issue.
</p>
<h4>Handling different input types</h4>
<p>
    Android text fields allow you to set a specific input type, such as free form text, numbers,
    URLs, email addresses, and search strings. When you implement a new IME, you need to
    detect the input type of each field and provide the appropriate interface for it. However, you
    don't have to set up your IME to check that the user entered text that's valid for the
    input type; that's the responsibility of the application that owns the text field.
</p>
<p>
    For example, here are screenshots of the interfaces that the Latin IME provided with the
    Android platform provides for text and phone number inputs:
</p>
<img src="{@docRoot}resources/articles/images/inputmethod_text_type_screenshot.png" alt=""
    height="142" id="figure2" />
<img src="{@docRoot}resources/articles/images/inputmethod_numeric_type_screenshot.png" alt=""
    height="120" id="figure2a" />
<p class="img-caption">
    <strong>Figure 2.</strong> Latin IME input types.
</p>
<p>
    When an input field receives focus and your IME starts, the system calls 
    {@link android.inputmethodservice.InputMethodService#onStartInputView(EditorInfo, boolean)
    onStartInputView()}, passing in an {@link android.view.inputmethod.EditorInfo} object that 
    contains details about the input type and other attributes of the text field. In this object, 
    the {@link android.view.inputmethod.EditorInfo#inputType} field contains the text field's input
    type.
</p>
<p>
    The {@link android.view.inputmethod.EditorInfo#inputType} field is an <code>int</code>
    that contains bit patterns for various input type settings. To test it for the text field's
    input type, mask it with the constant {@link android.text.InputType#TYPE_MASK_CLASS}, like
    this:
</p>
<pre>
inputType &amp; InputType.TYPE_MASK_CLASS 
</pre>
<p>
The input type bit pattern can have one of several values, including:
</p>
<dl>
    <dt>{@link android.text.InputType#TYPE_CLASS_NUMBER}</dt>
    <dd>
        A text field for entering numbers. As illustrated in the previous screen shot, the
        Latin IME displays a number pad for fields of this type.
    </dd>
    <dt>{@link android.text.InputType#TYPE_CLASS_DATETIME}</dt>
    <dd>
        A text field for entering a date and time.
    </dd>
    <dt>{@link android.text.InputType#TYPE_CLASS_PHONE}</dt>
    <dd>
        A text field for entering telephone numbers.
    </dd>
    <dt>{@link android.text.InputType#TYPE_CLASS_TEXT}</dt>
    <dd>
        A text field for entering all supported characters.
    </dd>
</dl>
<p>
    These constants are described in more detail in the reference documentation for 
    {@link android.text.InputType}.
</p>
<p>
    The {@link android.view.inputmethod.EditorInfo#inputType} field can contain other bits that
    indicate a variant of the text field type, such as:
</p>
<dl>
    <dt>{@link android.text.InputType#TYPE_TEXT_VARIATION_PASSWORD}</dt>
    <dd>
        A variant of {@link android.text.InputType#TYPE_CLASS_TEXT} for entering passwords. The
        input method will display dingbats instead of the actual text.
    </dd>
    <dt>{@link android.text.InputType#TYPE_TEXT_VARIATION_URI}</dt>
    <dd>
        A variant of {@link android.text.InputType#TYPE_CLASS_TEXT} for entering web URLs and
        other Uniform Resource Identifiers (URIs).
    </dd>
    <dt>{@link android.text.InputType#TYPE_TEXT_FLAG_AUTO_COMPLETE}</dt>
    <dd>
        A variant of {@link android.text.InputType#TYPE_CLASS_TEXT} for entering text that the
        application "auto-completes" from a dictionary, search, or other facility.
    </dd>
</dl>
<p>
    Remember to mask {@link android.view.inputmethod.EditorInfo#inputType} with the appropriate
    constant when you test for these variants. The available mask constants are listed in the
    reference documentation for {@link android.text.InputType}.
</p>
<p class="caution">
    <strong>Caution:</strong> In your own IME, make sure you handle text correctly when you send it
    to a password field. Hide the password in your UI both in the input view and in the candidates
    view. Also remember that you shouldn't store passwords on a device. To learn more, see the <a
        href="{@docRoot}guide/practices/security.html">Designing for Security</a> guide.
</p>
<h2 id="SendText">Sending Text to the Application</h2>
<p>
    As the user inputs text with your IME, you can send text to the application by
    sending individual key events or by editing the text around the cursor in the application's text
    field. In either case, you use an instance of {@link android.view.inputmethod.InputConnection} 
    to deliver the text. To get this instance, call 
    {@link android.inputmethodservice.InputMethodService#getCurrentInputConnection
    InputMethodService.getCurrentInputConnection()}.
</p>
<h3 id="EditingCursor">Editing the text around the cursor</h3>
<p>
    When you're handling the editing of existing text in a text field, some of the more useful
    methods in {@link android.view.inputmethod.BaseInputConnection} are:
</p>
<dl>
    <dt>
        {@link android.view.inputmethod.BaseInputConnection#getTextBeforeCursor(int, int)
        getTextBeforeCursor()}</dt>
    <dd>
        Returns a {@link java.lang.CharSequence} containing the number of requested characters
        before the current cursor position.
    </dd>
    <dt>
        {@link android.view.inputmethod.BaseInputConnection#getTextAfterCursor(int, int)
        getTextAfterCursor()}
    </dt>
    <dd>
        Returns a {@link java.lang.CharSequence} containing the number of requested characters
        following the current cursor position.
    </dd>
    <dt>
        {@link android.view.inputmethod.BaseInputConnection#deleteSurroundingText(int, int)
        deleteSurroundingText()}
    </dt>
    <dd>
        Deletes the specified number of characters before and following the current cursor
        position.
    </dd>
    <dt>
        {@link android.view.inputmethod.BaseInputConnection#commitText(CharSequence, int)
        commitText()}
    </dt>
    <dd>
        Commit a {@link java.lang.CharSequence} to the text field and set a new cursor
        position.
    </dd>
</dl>
<p>
    For example, the following snippet shows how to replace the text "Fell" to the left of the
    with the text "Hello!":
</p>
<pre>
    InputConnection ic = getCurrentInputConnection();
    
    ic.deleteSurroundingText(4, 0);
    
    ic.commitText("Hello", 1);
    
    ic.commitText("!", 1);
</pre>
<h3 id="ComposeThenCommit">Composing text before committing</h3>
<p>
    If your IME does text prediction or requires multiple steps to compose a glyph or
    word, you can show the progress in the text field until the user commits the word, and then you
    can replace the partial composition with the completed text. You may give special treatment to 
    the text by adding a "span" to it when you pass it to InputConnection#setComposingText().
</p>
<p>
    The following snippet shows how to show progress in a text field:
</p>
<pre>
    InputConnection ic = getCurrentInputConnection();

    ic.setComposingText("Composi", 1);
...

    ic.setComposingText("Composin", 1);

...

    ic.commitText("Composing ", 1);
</pre>
<p>
    The following screenshots show how this appears to the user:
</p>
<img src="{@docRoot}resources/articles/images/inputmethod_composing_text_1.png" alt="" height="54"
    id="figure3a" />
<img src="{@docRoot}resources/articles/images/inputmethod_composing_text_2.png" alt="" height="53"
    id="figure3b" />
<img src="{@docRoot}resources/articles/images/inputmethod_composing_text_3.png" alt="" height="31"
    id="figure3c" />
<p class="img-caption">
    <strong>Figure 3.</strong> Composing text before committing.
</p>
<h3 id="HardwareKeyEvents">Intercepting hardware key events</h3>
<p>
    Even though the input method window doesn't have explicit focus, it receives hardware key
    events first and can choose to consume them or forward them along to the application. For
    example, you may want to consume the directional keys to navigate within your UI for candidate
    selection during composition. You may also want to trap the back key to dismiss any popups
    originating from the input method window.</p>
<p>
    To intercept hardware keys, override 
    {@link android.inputmethodservice.InputMethodService#onKeyDown(int, KeyEvent) onKeyDown()}
    and {@link android.inputmethodservice.InputMethodService#onKeyUp(int, KeyEvent) onKeyUp()}. 
    See the <a href=”{@docRoot}resources/samples/SoftKeyboard/index.html”>Soft Keyboard</a> sample 
    app for an example.
</p>
<p>
    Remember to call the <code>super()</code> method for keys you don't want to handle yourself.
</p>
<h2 id="IMESubTypes">Creating an IME Subtype</h2>
<p>
    Subtypes allow the IME to expose multiple input modes and languages supported by an IME. A 
    subtype can represent:
</p>
<ul>
    <li>A locale such as en_US or fr_FR</li>
    <li>An input mode such as voice, keyboard, or handwriting</li>
    <li>
        Other input styles, forms, or properties specific to the IME, such as 10-key or qwerty
        keyboard layouts.
    </li>
</ul>
<p>
    Basically, the mode can be any text such as "keyboard", "voice", and so forth.
</p>
<p>A subtype can also expose a combination of these.</p>
<p>
    Subtype information is used for an IME switcher dialog that's available from the notification
    bar and also for IME settings. The information also allows the framework to bring up a
    specific subtype of an IME directly. When you build an IME, use the subtype facility, because 
    it helps the user identify and switch between different IME languages and modes.
</p>
<p>
    You define subtypes in one of the input method's XML resource files, using the
    <code>&lt;subtype&gt;</code> element. The following snippet defines an IME with two 
    subtypes: a keyboard subtype for the US English locale, and another keyboard subtype for the 
    French language locale for France:
</p>
<pre>
&lt;input-method xmlns:android="http://schemas.android.com/apk/res/android"
        android:settingsActivity="com.example.softkeyboard.Settings"
        android:icon="&#64;drawable/ime_icon"
    &lt;subtype android:name="&#64;string/display_name_english_keyboard_ime"
            android:icon="&#64;drawable/subtype_icon_english_keyboard_ime"
            android:imeSubtypeLanguage="en_US"
            android:imeSubtypeMode="keyboard"
            android:imeSubtypeExtraValue="somePrivateOption=true"
    /&gt;
    &lt;subtype android:name="&#64;string/display_name_french_keyboard_ime"
            android:icon="&#64;drawable/subtype_icon_french_keyboard_ime"
            android:imeSubtypeLanguage="fr_FR"
            android:imeSubtypeMode="keyboard"
            android:imeSubtypeExtraValue="foobar=30,someInternalOption=false"
    /&gt;
    &lt;subtype android:name="&#64;string/display_name_german_keyboard_ime"
            ...
    /&gt;
/&gt;
</pre>
<p>
    To ensure that your subtypes are labeled correctly in the UI, use %s to get a subtype label
    that is the same as the subtype’s locale label. This is demonstrated in the next two snippets.
    The first snippet shows part of the input method's XML file:
</p>
<pre>
    &lt;subtype
        android:label="&#64;string/label_subtype_generic"
        android:imeSubtypeLocale="en_US"
        android:icon="&#64;drawable/icon_en_us"
        android:imeSubtypeMode="keyboard" /&gt;
</pre>
<p>
    The next snippet is part of the IME's <code>strings.xml</code> file. The string 
    resource <code>label_subtype_generic</code>, which is used by the input method UI definition to 
    set the subtype's label, is defined as:
</p>
<pre>
&lt;string name="label_subtype_generic"&gt;%s&lt;/string&gt;
</pre>
<p>
    This sets the subtype’s display name to “English (United States)” in any English language
    locale, or to the appropriate localization in other locales.
</p>
<h3 id="SubtypeProcessing">Choosing IME subtypes from the notification bar</h3>
<p>
    The Android system manages all subtypes exposed by all IMEs. IME subtypes are
    treated as modes of the IME they belong to. In the notification bar, a user can select an
    available subtype for the currently-set IME, as shown in the following screenshot:
</p>
<img src="{@docRoot}resources/articles/images/inputmethod_subtype_notification.png" alt=""
    height="85" id="figure4" />
<p class="img-caption">
    <strong>Figure 4.</strong> Choosing an IME subtype from the notification bar.
</p>
<img src="{@docRoot}resources/articles/images/inputmethod_subtype_preferences.png" alt=""
    height="165" id="figure5" />
<p class="img-caption">
    <strong>Figure 5.</strong> Setting subtype preferences in System Settings.
</p>
<h3 id="SubtypeSettings">Choosing IME subtypes from System Settings</h3>
<p>
    A user can control how subtypes are used in the “Language &amp; input” settings panel in the
    System Settings area. In the Soft Keyboard sample, the file 
    <code>InputMethodSettingsFragment.java</code> contains an implementation that 
    facilitates a subtype enabler in the IME settings. Please refer to the SoftKeyboard sample in 
    the Android SDK for more information about how to support Input Method Subtypes in your IME.
</p>
<img src="{@docRoot}resources/articles/images/inputmethod_subtype_settings.png" alt=""
    height="210" id="figure6" />
<p class="img-caption">
    <strong>Figure 6.</strong> Choosing a language for the IME.
</p>
<h2 id="GeneralDesign">General IME Considerations</h2>
<p>
    Here are some other things to consider as you're implementing your IME:
</p>
<ul>
<li>
    Provide a way for users to set options directly from the IME's UI.
</li>
<li>
    Because multiple IMEs may be installed on the device, provide a way for the user to switch to a 
    different IME directly from the input method UI.
</li>
<li>
    Bring up the IME's UI quickly. Preload or load on demand any large resources so that users 
    see the IME as soon as they tap on a text field. Cache resources and views for subsequent 
    invocations of the input method.
</li>
<li>
    Conversely, you should release large memory allocations soon after the input method window is 
    hidden, so that applications can have sufficient memory to run. Consider using a delayed message
    to release resources if the IME is in a hidden state for a few seconds.
</li>    
<li>
    Make sure that users can enter as many characters as possible for the language or locale 
    associated with the IME. Remember that users may use punctuation in passwords or user 
    names, so your IME has to provide many different characters to allow users to enter a
    password and get access to the device.
</li>
</ul>