1page.title=Grid View
2page.tags=gridview
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
20two-dimensional,
21scrollable grid. The grid items are automatically inserted to the layout using a {@link
22android.widget.ListAdapter}.</p>
23
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
28<img src="{@docRoot}images/ui/gridview.png" alt="" />
29
30
31<h2 id="example">Example</h2>
32
33<p>In this tutorial, you'll create a grid of image thumbnails. When an item is selected, a
34toast 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
40href="{@docRoot}shareables/sample_images.zip">download these sample images</a>. Save the image files
41into 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&lt;?xml version="1.0" encoding="utf-8"?>
46&lt;GridView xmlns:android="http://schemas.android.com/apk/res/android"
47    android:id="@+id/gridview"
48    android:layout_width="match_parent"
49    android:layout_height="match_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
59self explanatory. For more information about valid attributes, see the {@link
60android.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>
65public 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&lt;?> 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
81android.app.Activity#findViewById(int)}. The {@link
82android.widget.GridView#setAdapter(T) setAdapter()} method then sets a custom adapter ({@code
83ImageAdapter}) as the source for all items to be displayed in the grid. The {@code ImageAdapter} is
84created in the next step.</p>
85<p>To do something when an item in the grid is clicked, the {@link
86android.widget.AdapterView#setOnItemClickListener(OnItemClickListener) setOnItemClickListener()}
87method is passed a new {@link android.widget.AdapterView.OnItemClickListener}. This anonymous
88instance defines the {@link
89android.widget.AdapterView.OnItemClickListener#onItemClick(AdapterView,View,int,long)
90onItemClick()} callback method to show a {@link android.widget.Toast} that displays the index
91position (zero-based) of the selected item (in a real world scenario, the position could be used to
92get the full sized
93image for some other task).</p>
94
95</li>
96<li>Create a new class called <code>ImageAdapter</code> that extends {@link
97android.widget.BaseAdapter}:
98<pre>
99public 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
151android.widget.BaseAdapter}. The constructor and {@link
152android.widget.Adapter#getCount()} are self-explanatory. Normally, {@link
153android.widget.Adapter#getItem(int)} should return the actual object at the specified position in
154the adapter, but it's ignored for this example. Likewise, {@link
155android.widget.Adapter#getItemId(int)} should return the row id of the item, but it's not
156needed here.</p>
157
158<p>The first method necessary is {@link android.widget.Adapter#getView(int,View,ViewGroup)
159getView()}. This method creates a new {@link android.view.View} for each image added to the {@code
160ImageAdapter}. When this is called, a {@link android.view.View} is passed in, which is normally a
161recycled object (at least after this has been called once), so there's a check to see if the
162object is null. If it <em>is</em> null, an {@link android.widget.ImageView} is instantiated and
163configured with desired properties for the image presentation:</p>
164<ul>
165  <li>{@link android.view.View#setLayoutParams(ViewGroup.LayoutParams)} sets
166the height and width for the View&mdash;this ensures that, no matter the size of the drawable, each
167image 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
169be cropped toward the center (if necessary).</li>
170  <li>{@link android.widget.ImageView#setPadding(int,int,int,int)} defines the padding for all
171sides. (Note that, if the images have different aspect-ratios, then less
172padding will cause more cropping of the image if it does not match
173the dimensions given to the ImageView.)</li>
174</ul>
175
176<p>If the {@link android.view.View} passed to {@link
177android.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}
179object.</p>
180
181<p>At the end of the {@link android.widget.Adapter#getView(int,View,ViewGroup) getView()} method,
182the {@code
183position} integer passed into the method is used to select an image from the {@code mThumbIds}
184array, 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
191android.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
196