Scott Main | c5e128c | 2012-07-25 11:51:12 -0700 | [diff] [blame] | 1 | page.title=Grid View |
Joe Fernandez | 33baa5a | 2013-11-14 11:41:19 -0800 | [diff] [blame] | 2 | page.tags=gridview |
Scott Main | 50e990c | 2012-06-21 17:14:39 -0700 | [diff] [blame] | 3 | @jd:body |
| 4 | <div id="qv-wrapper"> |
| 5 | <div id="qv"> |
| 6 | <h2>In this document</h2> |
| 7 | <ol> |
| 8 | <li><a href="#example">Example</a></li> |
| 9 | </ol> |
| 10 | <h2>Key classes</h2> |
| 11 | <ol> |
| 12 | <li>{@link android.widget.GridView}</li> |
| 13 | <li>{@link android.widget.ImageView}</li> |
| 14 | <li>{@link android.widget.BaseAdapter}</li> |
| 15 | <li>{@link android.widget.AdapterView.OnItemClickListener}</li> |
| 16 | </ol> |
| 17 | </div> |
| 18 | </div> |
| 19 | <p>{@link android.widget.GridView} is a {@link android.view.ViewGroup} that displays items in a |
| 20 | two-dimensional, |
| 21 | scrollable grid. The grid items are automatically inserted to the layout using a {@link |
| 22 | android.widget.ListAdapter}.</p> |
| 23 | |
Scott Main | 2d9063b | 2012-08-08 18:49:28 -0700 | [diff] [blame] | 24 | <p>For an introduction to how you can dynamically insert views using an adapter, read |
| 25 | <a href="{@docRoot}guide/topics/ui/declaring-layout.html#AdapterViews">Building Layouts with |
| 26 | an Adapter</a>.</p> |
| 27 | |
Scott Main | 50e990c | 2012-06-21 17:14:39 -0700 | [diff] [blame] | 28 | <img src="{@docRoot}images/ui/gridview.png" alt="" /> |
| 29 | |
| 30 | |
| 31 | <h2 id="example">Example</h2> |
Scott Main | 2d9063b | 2012-08-08 18:49:28 -0700 | [diff] [blame] | 32 | |
Scott Main | 50e990c | 2012-06-21 17:14:39 -0700 | [diff] [blame] | 33 | <p>In this tutorial, you'll create a grid of image thumbnails. When an item is selected, a |
| 34 | toast message will display the position of the image.</p> |
| 35 | |
| 36 | |
| 37 | <ol> |
| 38 | <li>Start a new project named <em>HelloGridView</em>.</li> |
| 39 | <li>Find some photos you'd like to use, or <a |
| 40 | href="{@docRoot}shareables/sample_images.zip">download these sample images</a>. Save the image files |
| 41 | into the project's |
| 42 | <code>res/drawable/</code> directory.</li> |
| 43 | <li>Open the <code>res/layout/main.xml</code> file and insert the following: |
| 44 | <pre> |
| 45 | <?xml version="1.0" encoding="utf-8"?> |
| 46 | <GridView xmlns:android="http://schemas.android.com/apk/res/android" |
| 47 | android:id="@+id/gridview" |
| 48 | android:layout_width="fill_parent" |
| 49 | android:layout_height="fill_parent" |
| 50 | android:columnWidth="90dp" |
| 51 | android:numColumns="auto_fit" |
| 52 | android:verticalSpacing="10dp" |
| 53 | android:horizontalSpacing="10dp" |
| 54 | android:stretchMode="columnWidth" |
| 55 | android:gravity="center" |
| 56 | /> |
| 57 | </pre> |
| 58 | <p>This {@link android.widget.GridView} will fill the entire screen. The attributes are rather |
| 59 | self explanatory. For more information about valid attributes, see the {@link |
| 60 | android.widget.GridView} reference.</p> |
| 61 | </li> |
| 62 | <li>Open <code>HelloGridView.java</code> and insert the following code for the |
| 63 | {@link android.app.Activity#onCreate(Bundle) onCreate()} method: |
| 64 | <pre> |
| 65 | public void onCreate(Bundle savedInstanceState) { |
| 66 | super.onCreate(savedInstanceState); |
| 67 | setContentView(R.layout.main); |
| 68 | |
| 69 | GridView gridview = (GridView) findViewById(R.id.gridview); |
| 70 | gridview.setAdapter(new ImageAdapter(this)); |
| 71 | |
| 72 | gridview.setOnItemClickListener(new OnItemClickListener() { |
| 73 | public void onItemClick(AdapterView<?> parent, View v, int position, long id) { |
| 74 | Toast.makeText(HelloGridView.this, "" + position, Toast.LENGTH_SHORT).show(); |
| 75 | } |
| 76 | }); |
| 77 | } |
| 78 | </pre> |
| 79 | <p>After the {@code main.xml} layout is set for the content view, the |
| 80 | {@link android.widget.GridView} is captured from the layout with {@link |
| 81 | android.app.Activity#findViewById(int)}. The {@link |
| 82 | android.widget.GridView#setAdapter(T) setAdapter()} method then sets a custom adapter ({@code |
| 83 | ImageAdapter}) as the source for all items to be displayed in the grid. The {@code ImageAdapter} is |
| 84 | created in the next step.</p> |
| 85 | <p>To do something when an item in the grid is clicked, the {@link |
| 86 | android.widget.AdapterView#setOnItemClickListener(OnItemClickListener) setOnItemClickListener()} |
| 87 | method is passed a new {@link android.widget.AdapterView.OnItemClickListener}. This anonymous |
| 88 | instance defines the {@link |
| 89 | android.widget.AdapterView.OnItemClickListener#onItemClick(AdapterView,View,int,long) |
| 90 | onItemClick()} callback method to show a {@link android.widget.Toast} that displays the index |
| 91 | position (zero-based) of the selected item (in a real world scenario, the position could be used to |
| 92 | get the full sized |
| 93 | image for some other task).</p> |
| 94 | |
| 95 | </li> |
| 96 | <li>Create a new class called <code>ImageAdapter</code> that extends {@link |
| 97 | android.widget.BaseAdapter}: |
| 98 | <pre> |
| 99 | public class ImageAdapter extends BaseAdapter { |
| 100 | private Context mContext; |
| 101 | |
| 102 | public ImageAdapter(Context c) { |
| 103 | mContext = c; |
| 104 | } |
| 105 | |
| 106 | public int getCount() { |
| 107 | return mThumbIds.length; |
| 108 | } |
| 109 | |
| 110 | public Object getItem(int position) { |
| 111 | return null; |
| 112 | } |
| 113 | |
| 114 | public long getItemId(int position) { |
| 115 | return 0; |
| 116 | } |
| 117 | |
| 118 | // create a new ImageView for each item referenced by the Adapter |
| 119 | public View getView(int position, View convertView, ViewGroup parent) { |
| 120 | ImageView imageView; |
| 121 | if (convertView == null) { // if it's not recycled, initialize some attributes |
| 122 | imageView = new ImageView(mContext); |
| 123 | imageView.setLayoutParams(new GridView.LayoutParams(85, 85)); |
| 124 | imageView.setScaleType(ImageView.ScaleType.CENTER_CROP); |
| 125 | imageView.setPadding(8, 8, 8, 8); |
| 126 | } else { |
| 127 | imageView = (ImageView) convertView; |
| 128 | } |
| 129 | |
| 130 | imageView.setImageResource(mThumbIds[position]); |
| 131 | return imageView; |
| 132 | } |
| 133 | |
| 134 | // references to our images |
| 135 | private Integer[] mThumbIds = { |
| 136 | R.drawable.sample_2, R.drawable.sample_3, |
| 137 | R.drawable.sample_4, R.drawable.sample_5, |
| 138 | R.drawable.sample_6, R.drawable.sample_7, |
| 139 | R.drawable.sample_0, R.drawable.sample_1, |
| 140 | R.drawable.sample_2, R.drawable.sample_3, |
| 141 | R.drawable.sample_4, R.drawable.sample_5, |
| 142 | R.drawable.sample_6, R.drawable.sample_7, |
| 143 | R.drawable.sample_0, R.drawable.sample_1, |
| 144 | R.drawable.sample_2, R.drawable.sample_3, |
| 145 | R.drawable.sample_4, R.drawable.sample_5, |
| 146 | R.drawable.sample_6, R.drawable.sample_7 |
| 147 | }; |
| 148 | } |
| 149 | </pre> |
| 150 | <p>First, this implements some required methods inherited from {@link |
| 151 | android.widget.BaseAdapter}. The constructor and {@link |
| 152 | android.widget.Adapter#getCount()} are self-explanatory. Normally, {@link |
| 153 | android.widget.Adapter#getItem(int)} should return the actual object at the specified position in |
| 154 | the adapter, but it's ignored for this example. Likewise, {@link |
| 155 | android.widget.Adapter#getItemId(int)} should return the row id of the item, but it's not |
| 156 | needed here.</p> |
| 157 | |
| 158 | <p>The first method necessary is {@link android.widget.Adapter#getView(int,View,ViewGroup) |
| 159 | getView()}. This method creates a new {@link android.view.View} for each image added to the {@code |
| 160 | ImageAdapter}. When this is called, a {@link android.view.View} is passed in, which is normally a |
| 161 | recycled object (at least after this has been called once), so there's a check to see if the |
| 162 | object is null. If it <em>is</em> null, an {@link android.widget.ImageView} is instantiated and |
| 163 | configured with desired properties for the image presentation:</p> |
| 164 | <ul> |
| 165 | <li>{@link android.view.View#setLayoutParams(ViewGroup.LayoutParams)} sets |
| 166 | the height and width for the View—this ensures that, no matter the size of the drawable, each |
| 167 | image is resized and cropped to fit in these dimensions, as appropriate.</li> |
| 168 | <li>{@link android.widget.ImageView#setScaleType(ImageView.ScaleType)} declares that images should |
| 169 | be cropped toward the center (if necessary).</li> |
| 170 | <li>{@link android.widget.ImageView#setPadding(int,int,int,int)} defines the padding for all |
| 171 | sides. (Note that, if the images have different aspect-ratios, then less |
Scott Main | 6aad995 | 2013-01-07 18:51:49 -0800 | [diff] [blame] | 172 | padding will cause more cropping of the image if it does not match |
Scott Main | 50e990c | 2012-06-21 17:14:39 -0700 | [diff] [blame] | 173 | the dimensions given to the ImageView.)</li> |
| 174 | </ul> |
| 175 | |
| 176 | <p>If the {@link android.view.View} passed to {@link |
| 177 | android.widget.Adapter#getView(int,View,ViewGroup) getView()} is <em>not</em> null, then the local |
| 178 | {@link android.widget.ImageView} is initialized with the recycled {@link android.view.View} |
| 179 | object.</p> |
| 180 | |
| 181 | <p>At the end of the {@link android.widget.Adapter#getView(int,View,ViewGroup) getView()} method, |
| 182 | the {@code |
| 183 | position} integer passed into the method is used to select an image from the {@code mThumbIds} |
| 184 | array, which is set as the image resource for the {@link android.widget.ImageView}.</p> |
| 185 | <p>All that's left is to define the {@code mThumbIds} array of drawable resources.</p> |
| 186 | </li> |
| 187 | <li>Run the application.</li> |
| 188 | </ol> |
| 189 | |
| 190 | <p>Try experimenting with the behaviors of the {@link android.widget.GridView} and {@link |
| 191 | android.widget.ImageView} elements by adjusting their properties. For example, instead of using |
| 192 | {@link android.view.View#setLayoutParams(ViewGroup.LayoutParams)}, try using |
| 193 | {@link android.widget.ImageView#setAdjustViewBounds(boolean)}. </p> |
| 194 | |
| 195 | |