1 page.title=Checkboxes 2 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.CheckBox}</li> 15 </ol> 16 </div> 17 </div> 18 19 <p>Checkboxes allow the user to select one or more options from a set. Typically, you should 20 present each checkbox option in a vertical list.</p> 21 22 <img src="{@docRoot}images/ui/checkboxes.png" alt="" /> 23 24 <p>To create each checkbox option, create a {@link android.widget.CheckBox} in your layout. Because 25 a set of checkbox options allows the user to select multiple items, each checkbox is managed 26 separately and you must register a click listener for each one.</p> 27 28 <h2 id="HandlingEvents">Responding to Click Events</h2> 29 30 <p>When the user selects a checkbox, the {@link android.widget.CheckBox} object receives an 31 on-click event.</p> 32 33 <p>To define the click event handler for a checkbox, add the <code><a 34 href="/reference/android/R.attr.html#onClick">android:onClick</a></code> attribute to the 35 <code><CheckBox></code> element in your XML 36 layout. The value for this attribute must be the name of the method you want to call in response 37 to a click event. The {@link android.app.Activity} hosting the layout must then implement the 38 corresponding method.</p> 39 40 <p>For example, here are a couple {@link android.widget.CheckBox} objects in a list:</p> 41 42 <pre> 43 <?xml version="1.0" encoding="utf-8"?> 44 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 45 android:orientation="vertical" 46 android:layout_width="fill_parent" 47 android:layout_height="fill_parent"> 48 <CheckBox android:id="@+id/checkbox_meat" 49 android:layout_width="wrap_content" 50 android:layout_height="wrap_content" 51 android:text="@string/meat" 52 android:onClick="onCheckboxClicked"/> 53 <CheckBox android:id="@+id/checkbox_cheese" 54 android:layout_width="wrap_content" 55 android:layout_height="wrap_content" 56 android:text="@string/cheese" 57 android:onClick="onCheckboxClicked"/> 58 </LinearLayout> 59 </pre> 60 61 <p>Within the {@link android.app.Activity} that hosts this layout, the following method handles the 62 click event for both checkboxes:</p> 63 64 <pre> 65 public void onCheckboxClicked(View view) { 66 // Is the view now checked? 67 boolean checked = ((CheckBox) view).isChecked(); 68 69 // Check which checkbox was clicked 70 switch(view.getId()) { 71 case R.id.checkbox_meat: 72 if (checked) 73 // Put some meat on the sandwich 74 else 75 // Remove the meat 76 break; 77 case R.id.checkbox_cheese: 78 if (checked) 79 // Cheese me 80 else 81 // I'm lactose intolerant 82 break; 83 // TODO: Veggie sandwich 84 } 85 } 86 </pre> 87 88 <p>The method you declare in the {@link android.R.attr#onClick android:onClick} attribute 89 must have a signature exactly as shown above. Specifically, the method must:</p> 90 <ul> 91 <li>Be public</li> 92 <li>Return void</li> 93 <li>Define a {@link android.view.View} as its only parameter (this will be the {@link 94 android.view.View} that was clicked)</li> 95 </ul> 96 97 <p class="note"><strong>Tip:</strong> If you need to change the checkbox state 98 yourself (such as when loading a saved {@link android.preference.CheckBoxPreference}), 99 use the {@link android.widget.CompoundButton#setChecked(boolean)} or {@link 100 android.widget.CompoundButton#toggle()} method.</p>
