1 page.title=Building a Flexible UI 2 3 trainingnavtop=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 19 Handsets</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" 26 class="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 35 fragments in different layout configurations to optimize the user experience based on the available 36 screen space.</p> 37 38 <p>For example, on a handset device it might be appropriate to display just one fragment at a time 39 for a single-pane user interface. Conversely, you may want to set fragments side-by-side on a 40 tablet 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 44 configurations for the same activity on different screen sizes. On a large screen, both fragments 45 fit side by side, but on a handset device, only one fragment fits at a time so the fragments must 46 replace 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, 49 remove, 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 57 a fragment to the activity during the activity runtime. This is necessary 58 if you plan to change fragments during the life of the activity.</p> 59 60 <p>To perform a transaction such as add or 61 remove 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, 63 and perform other fragment transactions.</p> 64 65 <p>If your activity allows the fragments to be removed and replaced, you should add the 66 initial 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 70 runtime—is that the fragment must have a container {@link android.view.View} in the layout in 71 which the fragment's layout will reside.</p> 72 73 <p>The following layout is an alternative to the layout shown in the <a 74 href="creating.html">previous lesson</a> that shows only one fragment at a time. In order to replace 75 one fragment with another, the activity's layout 76 includes 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 79 directory does <em>not</em> have the <code>large</code> qualifier, so this layout is used when the 80 device screen is smaller than <em>large</em> because the screen does not fit both fragments at 81 the 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 92 android.support.v4.app.FragmentActivity#getSupportFragmentManager()} to get a {@link 93 android.support.v4.app.FragmentManager} using the Support Library APIs. Then call {@link 94 android.support.v4.app.FragmentManager#beginTransaction} to create a {@link 95 android.support.v4.app.FragmentTransaction} and call {@link 96 android.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 99 android.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> 105 import android.os.Bundle; 106 import android.support.v4.app.FragmentActivity; 107 108 public 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 a new Fragment to be placed in the activity layout 126 HeadlinesFragment firstFragment = new HeadlinesFragment(); 127 128 // In case this activity was started with special instructions from an 129 // Intent, 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 141 runtime—instead of defining it in the activity's layout with a {@code <fragment>} 142 element—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 149 android.support.v4.app.FragmentTransaction#replace replace()} method instead of {@link 150 android.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 153 often appropriate to allow the user to navigate backward and "undo" the change. To allow the user 154 to navigate backward through the fragment transactions, you must call {@link 155 android.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 159 to the back stack, the fragment that is removed is stopped (not destroyed). If the user navigates 160 back to restore the fragment, it restarts. If you <em>do not</em> add the transaction to the back 161 stack, 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 167 ArticleFragment newFragment = new ArticleFragment(); 168 Bundle args = new Bundle(); 169 args.putInt(ArticleFragment.ARG_POSITION, position); 170 newFragment.setArguments(args); 171 172 FragmentTransaction 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 176 transaction.replace(R.id.fragment_container, newFragment); 177 transaction.addToBackStack(null); 178 179 // Commit the transaction 180 transaction.commit(); 181 </pre> 182 183 <p>The {@link android.support.v4.app.FragmentTransaction#addToBackStack addToBackStack()} method 184 takes an optional string parameter that specifies a unique name for the transaction. The name isn't 185 needed unless you plan to perform advanced fragment operations using the {@link 186 android.support.v4.app.FragmentManager.BackStackEntry} APIs.</p> 187 188 189 190 191
