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1page.title=Radio Buttons
2page.tags="radiobutton","radiogroup"
3@jd:body
4
5<div id="qv-wrapper">
6<div id="qv">
7<h2>In this document</h2>
8<ol>
9  <li><a href="#HandlingEvents">Responding to Click Events</a></li>
10</ol>
11
12<h2>Key classes</h2>
13<ol>
14  <li>{@link android.widget.RadioButton}</li>
15  <li>{@link android.widget.RadioGroup}</li>
16</ol>
17</div>
18</div>
19
20<p>Radio buttons allow the user to select one option from a set. You should use radio buttons for
21optional sets that are mutually exclusive if you think that the user needs to see all available
22options side-by-side. If it's not necessary to show all options side-by-side, use a <a
23href="{@docRoot}guide/topics/ui/controls/spinner.html">spinner</a> instead.</p>
24
25<img src="{@docRoot}images/ui/radiobuttons.png" alt="" />
26
27<p>To create each radio button option, create a {@link android.widget.RadioButton} in your layout.
28However, because radio buttons are mutually exclusive, you must group them together inside a
29{@link android.widget.RadioGroup}. By grouping them together, the system ensures that only one
30radio button can be selected at a time.</p>
31
32<h2 id="HandlingEvents">Responding to Click Events</h2>
33
34<p>When the user selects one of the radio buttons, the corresponding {@link
35android.widget.RadioButton} object receives an on-click event.</p>
36
37<p>To define the click event handler for a button, add the <code><a
38href="/reference/android/R.attr.html#onClick">android:onClick</a></code> attribute to the
39<code>&lt;RadioButton&gt;</code> element in your XML
40layout. The value for this attribute must be the name of the method you want to call in response
41to a click event. The {@link android.app.Activity} hosting the layout must then implement the
42corresponding method.</p>
43
44<p>For example, here are a couple {@link android.widget.RadioButton} objects:</p>
45
46<pre>
47&lt;?xml version="1.0" encoding="utf-8"?>
48&lt;RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
49    android:layout_width="fill_parent"
50    android:layout_height="wrap_content"
51    android:orientation="vertical">
52    &lt;RadioButton android:id="@+id/radio_pirates"
53        android:layout_width="wrap_content"
54        android:layout_height="wrap_content"
55        android:text="@string/pirates"
56        android:onClick="onRadioButtonClicked"/>
57    &lt;RadioButton android:id="@+id/radio_ninjas"
58        android:layout_width="wrap_content"
59        android:layout_height="wrap_content"
60        android:text="@string/ninjas"
61        android:onClick="onRadioButtonClicked"/>
62&lt;/RadioGroup>
63</pre>
64
65<p class="note"><strong>Note:</strong> The {@link android.widget.RadioGroup} is a subclass of
66{@link android.widget.LinearLayout} that has a vertical orientation by default.</p>
67
68<p>Within the {@link android.app.Activity} that hosts this layout, the following method handles the
69click event for both radio buttons:</p>
70
71<pre>
72public void onRadioButtonClicked(View view) {
73    // Is the button now checked?
74    boolean checked = ((RadioButton) view).isChecked();
75
76    // Check which radio button was clicked
77    switch(view.getId()) {
78        case R.id.radio_pirates:
79            if (checked)
80                // Pirates are the best
81            break;
82        case R.id.radio_ninjas:
83            if (checked)
84                // Ninjas rule
85            break;
86    }
87}
88</pre>
89
90<p>The method you declare in the {@link android.R.attr#onClick android:onClick} attribute
91must have a signature exactly as shown above. Specifically, the method must:</p>
92<ul>
93  <li>Be public</li>
94  <li>Return void</li>
95  <li>Define a {@link android.view.View} as its only parameter (this will be the {@link
96android.view.View} that was clicked)</li>
97</ul>
98
99<p class="note"><strong>Tip:</strong> If you need to change the radio button state
100yourself (such as when loading a saved {@link android.preference.CheckBoxPreference}),
101use the {@link android.widget.CompoundButton#setChecked(boolean)} or {@link
102android.widget.CompoundButton#toggle()} method.</p>
103