1 page.title=Radio Buttons 2 parent.title=Input Controls 3 parent.link=../controls.html 4 @jd:body 5 6 <div id="qv-wrapper"> 7 <div id="qv"> 8 <h2>In this document</h2> 9 <ol> 10 <li><a href="#HandlingEvents">Responding to Click Events</a></li> 11 </ol> 12 13 <h2>Key classes</h2> 14 <ol> 15 <li>{@link android.widget.RadioButton}</li> 16 <li>{@link android.widget.RadioGroup}</li> 17 </ol> 18 </div> 19 </div> 20 21 <p>Radio buttons allow the user to select one option from a set. You should use radio buttons for 22 optional sets that are mutually exclusive if you think that the user needs to see all available 23 options side-by-side. If it's not necessary to show all options side-by-side, use a <a 24 href="{@docRoot}guide/topics/ui/controls/spinner.html">spinner</a> instead.</p> 25 26 <img src="{@docRoot}images/ui/radiobuttons.png" alt="" /> 27 28 <p>To create each radio button option, create a {@link android.widget.RadioButton} in your layout. 29 However, because radio buttons are mutually exclusive, you must group them together inside a 30 {@link android.widget.RadioGroup}. By grouping them together, the system ensures that only one 31 radio button can be selected at a time.</p> 32 33 <h2 id="HandlingEvents">Responding to Click Events</h2> 34 35 <p>When the user selects one of the radio buttons, the corresponding {@link 36 android.widget.RadioButton} object receives an on-click event.</p> 37 38 <p>To define the click event handler for a button, add the <code><a 39 href="/reference/android/R.attr.html#onClick">android:onClick</a></code> attribute to the 40 <code><RadioButton></code> element in your XML 41 layout. The value for this attribute must be the name of the method you want to call in response 42 to a click event. The {@link android.app.Activity} hosting the layout must then implement the 43 corresponding method.</p> 44 45 <p>For example, here are a couple {@link android.widget.RadioButton} objects:</p> 46 47 <pre> 48 <?xml version="1.0" encoding="utf-8"?> 49 <RadioGroup xmlns:android="http://schemas.android.com/apk/res/android" 50 android:layout_width="fill_parent" 51 android:layout_height="wrap_content" 52 android:orientation="vertical"> 53 <RadioButton android:id="@+id/radio_pirates" 54 android:layout_width="wrap_content" 55 android:layout_height="wrap_content" 56 android:text="@string/pirates" 57 android:onClick="onRadioButtonClicked"/> 58 <RadioButton android:id="@+id/radio_ninjas" 59 android:layout_width="wrap_content" 60 android:layout_height="wrap_content" 61 android:text="@string/ninjas" 62 android:onClick="onRadioButtonClicked"/> 63 </RadioGroup> 64 </pre> 65 66 <p class="note"><strong>Note:</strong> The {@link android.widget.RadioGroup} is a subclass of 67 {@link android.widget.LinearLayout} that has a vertical orientation by default.</p> 68 69 <p>Within the {@link android.app.Activity} that hosts this layout, the following method handles the 70 click event for both radio buttons:</p> 71 72 <pre> 73 public void onRadioButtonClicked(View view) { 74 // Is the button now checked? 75 boolean checked = ((RadioButton) view).isChecked(); 76 77 // Check which radio button was clicked 78 switch(view.getId()) { 79 case R.id.radio_pirates: 80 if (checked) 81 // Pirates are the best 82 break; 83 case R.id.radio_ninjas: 84 if (checked) 85 // Ninjas rule 86 break; 87 } 88 } 89 </pre> 90 91 <p>The method you declare in the {@link android.R.attr#onClick android:onClick} attribute 92 must have a signature exactly as shown above. Specifically, the method must:</p> 93 <ul> 94 <li>Be public</li> 95 <li>Return void</li> 96 <li>Define a {@link android.view.View} as its only parameter (this will be the {@link 97 android.view.View} that was clicked)</li> 98 </ul> 99 100 <p class="note"><strong>Tip:</strong> If you need to change the radio button state 101 yourself (such as when loading a saved {@link android.preference.CheckBoxPreference}), 102 use the {@link android.widget.CompoundButton#setChecked(boolean)} or {@link 103 android.widget.CompoundButton#toggle()} method.</p> 104
