1page.title=Building a Flexible UI 2 3trainingnavtop=true 4 5@jd:body 6 7<div id="tb-wrapper"> 8 <div id="tb"> 9 <h2>This lesson teaches you to</h2> 10<ol> 11 <li><a href="#AddAtRuntime">Add a Fragment to an Activity at Runtime</a></li> 12 <li><a href="#Replace">Replace One Fragment with Another</a></li> 13</ol> 14 15 <h2>You should also read</h2> 16 <ul> 17 <li><a href="{@docRoot}guide/components/fragments.html">Fragments</a></li> 18 <li><a href="{@docRoot}guide/practices/tablets-and-handsets.html">Supporting Tablets and 19Handsets</a></li> 20 </ul> 21 22<h2>Try it out</h2> 23 24<div class="download-box"> 25 <a href="http://developer.android.com/shareables/training/FragmentBasics.zip" 26class="button">Download the sample</a> 27 <p class="filename">FragmentBasics.zip</p> 28</div> 29 30 </div> 31</div> 32 33 34<p>When designing your application to support a wide range of screen sizes, you can reuse your 35fragments in different layout configurations to optimize the user experience based on the available 36screen space.</p> 37 38<p>For example, on a handset device it might be appropriate to display just one fragment at a time 39for a single-pane user interface. Conversely, you may want to set fragments side-by-side on a 40tablet which has a wider screen size to display more information to the user.</p> 41 42<img src="{@docRoot}images/training/basics/fragments-screen-mock.png" alt="" /> 43<p class="img-caption"><strong>Figure 1.</strong> Two fragments, displayed in different 44configurations for the same activity on different screen sizes. On a large screen, both fragments 45fit side by side, but on a handset device, only one fragment fits at a time so the fragments must 46replace each other as the user navigates.</p> 47 48<p>The {@link android.support.v4.app.FragmentManager} class provides methods that allow you to add, 49remove, and replace fragments to an activity at runtime in order to create a dynamic experience.</p> 50 51 52 53<h2 id="AddAtRuntime">Add a Fragment to an Activity at Runtime</h2> 54 55<p>Rather than defining the fragments for an activity in the layout file—as shown in the 56<a href="creating.html">previous lesson</a> with the {@code <fragment>} element—you can add 57a fragment to the activity during the activity runtime. This is necessary 58if you plan to change fragments during the life of the activity.</p> 59 60<p>To perform a transaction such as add or 61remove a fragment, you must use the {@link android.support.v4.app.FragmentManager} to create a 62{@link android.support.v4.app.FragmentTransaction}, which provides APIs to add, remove, replace, 63and perform other fragment transactions.</p> 64 65<p>If your activity allows the fragments to be removed and replaced, you should add the 66initial fragment(s) to the activity during the activity's 67{@link android.app.Activity#onCreate onCreate()} method.</p> 68 69<p>An important rule when dealing with fragments—especially those that you add at 70runtime—is that the fragment must have a container {@link android.view.View} in the layout in 71which the fragment's layout will reside.</p> 72 73<p>The following layout is an alternative to the layout shown in the <a 74href="creating.html">previous lesson</a> that shows only one fragment at a time. In order to replace 75one fragment with another, the activity's layout 76includes an empty {@link android.widget.FrameLayout} that acts as the fragment container.</p> 77 78<p>Notice that the filename is the same as the layout file in the previous lesson, but the layout 79directory does <em>not</em> have the <code>large</code> qualifier, so this layout is used when the 80device screen is smaller than <em>large</em> because the screen does not fit both fragments at 81the same time.</p> 82 83<p><code>res/layout/news_articles.xml:</code></p> 84<pre> 85<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 86 android:id="@+id/fragment_container" 87 android:layout_width="match_parent" 88 android:layout_height="match_parent" /> 89</pre> 90 91<p>Inside your activity, call {@link 92android.support.v4.app.FragmentActivity#getSupportFragmentManager()} to get a {@link 93android.support.v4.app.FragmentManager} using the Support Library APIs. Then call {@link 94android.support.v4.app.FragmentManager#beginTransaction} to create a {@link 95android.support.v4.app.FragmentTransaction} and call {@link 96android.support.v4.app.FragmentTransaction#add add()} to add a fragment.</p> 97 98<p>You can perform multiple fragment transaction for the activity using the same {@link 99android.support.v4.app.FragmentTransaction}. When you're ready to make the changes, you must call 100{@link android.support.v4.app.FragmentTransaction#commit()}.</p> 101 102<p>For example, here's how to add a fragment to the previous layout:</p> 103 104<pre> 105import android.os.Bundle; 106import android.support.v4.app.FragmentActivity; 107 108public class MainActivity extends FragmentActivity { 109 @Override 110 public void onCreate(Bundle savedInstanceState) { 111 super.onCreate(savedInstanceState); 112 setContentView(R.layout.news_articles); 113 114 // Check that the activity is using the layout version with 115 // the fragment_container FrameLayout 116 if (findViewById(R.id.fragment_container) != null) { 117 118 // However, if we're being restored from a previous state, 119 // then we don't need to do anything and should return or else 120 // we could end up with overlapping fragments. 121 if (savedInstanceState != null) { 122 return; 123 } 124 125 // Create an instance of ExampleFragment 126 HeadlinesFragment firstFragment = new HeadlinesFragment(); 127 128 // In case this activity was started with special instructions from an Intent, 129 // pass the Intent's extras to the fragment as arguments 130 firstFragment.setArguments(getIntent().getExtras()); 131 132 // Add the fragment to the 'fragment_container' FrameLayout 133 getSupportFragmentManager().beginTransaction() 134 .add(R.id.fragment_container, firstFragment).commit(); 135 } 136 } 137} 138</pre> 139 140<p>Because the fragment has been added to the {@link android.widget.FrameLayout} container at 141runtime—instead of defining it in the activity's layout with a {@code <fragment>} 142element—the activity can remove the fragment and replace it with a different one.</p> 143 144 145 146<h2 id="Replace">Replace One Fragment with Another</h2> 147 148<p>The procedure to replace a fragment is similar to adding one, but requires the {@link 149android.support.v4.app.FragmentTransaction#replace replace()} method instead of {@link 150android.support.v4.app.FragmentTransaction#add add()}.</p> 151 152<p>Keep in mind that when you perform fragment transactions, such as replace or remove one, it's 153often appropriate to allow the user to navigate backward and "undo" the change. To allow the user 154to navigate backward through the fragment transactions, you must call {@link 155android.support.v4.app.FragmentTransaction#addToBackStack addToBackStack()} before you commit the 156{@link android.support.v4.app.FragmentTransaction}.</p> 157 158<p class="note"><strong>Note:</strong> When you remove or replace a fragment and add the transaction 159to the back stack, the fragment that is removed is stopped (not destroyed). If the user navigates 160back to restore the fragment, it restarts. If you <em>do not</em> add the transaction to the back 161stack, then the fragment is destroyed when removed or replaced.</p> 162 163<p>Example of replacing one fragment with another:</p> 164 165<pre> 166// Create fragment and give it an argument specifying the article it should show 167ArticleFragment newFragment = new ArticleFragment(); 168Bundle args = new Bundle(); 169args.putInt(ArticleFragment.ARG_POSITION, position); 170newFragment.setArguments(args); 171 172FragmentTransaction transaction = getSupportFragmentManager().beginTransaction(); 173 174// Replace whatever is in the fragment_container view with this fragment, 175// and add the transaction to the back stack so the user can navigate back 176transaction.replace(R.id.fragment_container, newFragment); 177transaction.addToBackStack(null); 178 179// Commit the transaction 180transaction.commit(); 181</pre> 182 183<p>The {@link android.support.v4.app.FragmentTransaction#addToBackStack addToBackStack()} method 184takes an optional string parameter that specifies a unique name for the transaction. The name isn't 185needed unless you plan to perform advanced fragment operations using the {@link 186android.support.v4.app.FragmentManager.BackStackEntry} APIs.</p> 187 188 189 190 191
