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diff --git a/docs/html/guide/topics/views/layout.jd b/docs/html/guide/topics/views/layout.jd new file mode 100644 index 0000000..f6eedbb --- /dev/null +++ b/docs/html/guide/topics/views/layout.jd @@ -0,0 +1,188 @@ +page.title=Common Layout Objects +@jd:body + +<p>The sections below describe some of the more common types of layout objects you'll be likely to use in your applications. Like other layouts, they are subclasses of {@link android.view.ViewGroup ViewGroup}.</p> + +<h2>FrameLayout<a name="framelayout" id="framelayout"></a></h2> + +<p>{@link android.widget.FrameLayout FrameLayout} is the simplest layout +object. It is intended as a blank reserved space on your screen that you can +later fill with a single object — for example, a picture that you'll swap out. +All child elements are pinned to the top left corner of the screen; you cannot +specify a location for a child of a {@link android.widget.FrameLayout +FrameLayout}. Later children will simply be drawn over earlier objects, +partially or totally obscuring them (unless the newer object is transparent). +</p> + +<h2>LinearLayout<a name="linearlayout" id="linearlayout"></a></h2> + +<p>A {@link android.widget.LinearLayout LinearLayout} aligns all children in a +single direction — vertically or horizontally, depending on what property you +set on the {@link android.widget.LinearLayout LinearLayout}. All children are +stacked one after the other, so a vertical list will only have one child per +row, no matter how wide they are, and a horizontal list will only be one row +high (the height of the tallest child, plus padding). {@link +android.widget.LinearLayout LinearLayout} respects margins between children, +and also <em>gravity</em> (right, center, or left alignment of a child). </p> + +<p>{@link android.widget.LinearLayout LinearLayout} also supports assigning a +<em>weight</em> to individual children. This value allows children to expand +to fill any remaining space on a screen. This prevents a list of small objects +from being bunched to one end of a large screen, allowing them to expand to +fill the space. Children specify a weight value, and any remaining space is +assigned to children in the proportion of their declared weight. Default +weight is zero. So, for example, if there are three text boxes, and two of +them declare a weight of 1, two of them will expand equally to fill the +remaining space, and the third will not grow any additional amount.</p> + +<div class="sidebox"> +<p><strong>Tip</strong>: To create a proportionate size +layout on the screen, create a container object that is fill_parent, assign +the children heights or widths of zero, and then assign relative weight values +to each child, depending on what proportion of the screen each should +take.</p> +</div> + +<p>The following two forms represent a {@link android.widget.LinearLayout LinearLayout} with a set of elements: a +button, some labels, some text boxes. Both have padding values to adjust the +padding nicely. The text boxes have their width set to <code>FILL_PARENT</code>; other +elements are set to <code>WRAP_CONTENT</code>. The gravity, by default, is left. The form +on the left has weight values unset (0 by default); the form on the right has +the comments text box weight set to 1. If the Name textbox had also been set +to 1, the Name and Comments text boxes would be the same height. </p> + +<p> + <img src="{@docRoot}images/linearlayout.png" alt="Linear layout with +weight attribute." width="421" height="348" /> +</p> + +<p>Within a horizontal {@link android.widget.LinearLayout LinearLayout}, items are aligned by the position of +their text base line (the first line of the first list element — topmost or +leftmost — is considered the reference line). This is so that people scanning +elements in a form shouldn't have to jump up and down to read element text in +neighboring elements. This can be turned off by setting +<code>android:baselineAligned="false"</code> in the layout XML. </p> + +<h2>TableLayout<a name="tablelayout" id="tablelayout"></a></h2> + +<p>{@link android.widget.TableLayout TableLayout} positions its children into rows + and columns. A TableLayout consists of a number of TableRow objects, + each defining a row (actually, you can have other children, which will be explained + below). TableLayout containers do not display border lines for their rows, columns, + or cells. Each row has zero or more cells; each cell can hold one View object. + The table has as many columns as the row with the most cells. A table can leave +cells empty. Cells cannot span columns, as they can in HTML. The following image + shows a table layout, with the invisible cell borders displayed as dotted lines. </p> +<p><img src="{@docRoot}images/table_layout.png" alt="TableLayout example" width="499" height="348" /></p> +<p>Columns can be hidden, can be marked to stretch to fill available screen space, + or can be marked as shrinkable to force the column to shrink until the table + fits the screen. See the reference documentation for this class for more details. </p> +<h2>AbsoluteLayout<a name="absolutelayout" id="absolutelayout"></a></h2> +<p>{@link android.widget.AbsoluteLayout AbsoluteLayout} enables children to specify + exact x/y coordinates to display on the screen, where (0,0) is the upper left + corner, and values increase as you move down or to the right. Margins are not + supported, and overlapping elements are allowed (although not recommended). We + generally recommend against using AbsoluteLayout unless you have good reasons + to use it, because it is fairly rigid and does not work well with different device + displays. </p> +<h2>RelativeLayout<a name="relativelayout" id="relativelayout"></a></h2> +<p>{@link android.widget.RelativeLayout RelativeLayout} lets children specify their + position relative to each other (specified by ID), or to the parent. So you can + align two elements by right border, or make one below another, or centered in + the screen. Elements are rendered in the order given, so if the first element + is centered in the screen, other elements aligning themselves to that element + will be aligned relative to screen center. If using XML to specify this layout + (as described later), a referenced element must be listed before you refer to + it. </p> +<p>Here is an example relative layout with the visible and invisible elements outlined. + The root screen layout object is a RelativeLayout object. </p> +<p><img src="{@docRoot}images/designing_ui_relative_layout.png" alt="RelativeLayout screen with elements highlighted." width="692" height="440" /></p> +<p>This diagram shows the class names of the screen elements, followed by a list + of the properties of each. Some of these properties are supported directly by + the element, and some are supported by its LayoutParams member (subclass RelativeLayout + for all the elements in this screen, because all elements are children of a RelativeLayout + parent object). The RelativeLayout parameters are width, height, below, alignTop, + toLeft, padding, and marginLeft. Note that some of these parameters support values + relative to other children — hence the name RelativeLayout. These include the + toLeft, alignTop, and below properties, which indicate the object to the left, + top, and below respectively. </p> +<h2>Summary of Important View Groups<a name="viewgroupsummary" id="viewgroupsummary"></a></h2> +<p>These objects all hold child UI elements. Some provide visible UI, and others + only handle child layout. </p> +<table width="100%" border="1"> + <tr> + <th scope="col">Class</th> + <th scope="col">Description</th> + </tr> + <tr> + <td>{@link android.widget.AbsoluteLayout AbsoluteLayout}<br /></td> + <td>Enables you to specify the location of child objects relative to the + parent in exact measurements (for example, pixels). </td> + </tr> + <tr> + <td>{@link android.widget.FrameLayout FrameLayout}</td> + <td>Layout that acts as a view frame to display + a single object. </td> + </tr> + <tr> + <td>{@link android.widget.Gallery Gallery} </td> + <td>A horizontal scrolling display of images, from a bound list. </td> + </tr> + <tr> + <td>{@link android.widget.GridView GridView} </td> + <td>Displays a scrolling grid of m columns and n rows.</td> + </tr> + <tr> + <td>{@link android.widget.LinearLayout LinearLayout} </td> + <td>A layout that organizes its children into a single horizontal or vertical + row. It creates a scrollbar if the length of the window exceeds the length + of the screen. </td> + </tr> + <tr> + <td>{@link android.widget.ListView ListView} </td> + <td>Displays a scrolling single column list. </td> + </tr> + <tr> + <td>{@link android.widget.RelativeLayout RelativeLayout} </td> + <td>Enables you to specify the location of child objects relative to each + other (child A to the left of child B) or to the parent (aligned to the + top of the parent). </td> + </tr> + <tr> + <td>{@link android.widget.ScrollView ScrollView} </td> + <td>A vertically scrolling column of elements. </td> + </tr> + <tr> + <td>{@link android.widget.Spinner Spinner} </td> + <td>Displays a single item at a time from a bound list, inside a one-row + textbox. Rather like a one-row listbox that can scroll either horizontally + or vertically. </td> + </tr> + <tr> + <td>{@link android.view.SurfaceView SurfaceView} </td> + <td>Provides direct access to a dedicated drawing surface. It can hold child + views layered on top of the surface, but is intended for applications + that need to draw pixels, rather than using widgets. </td> + </tr> + <tr> + <td>{@link android.widget.TabHost TabHost} </td> + <td>Provides a tab selection list that monitors clicks and enables the application + to change the screen whenever a tab is clicked. </td> + </tr> + <tr> + <td>{@link android.widget.TableLayout TableLayout} </td> + <td>A tabular layout with an arbitrary number of rows and columns, each cell + holding the widget of your choice. The rows resize to fit the largest + column. The cell borders are not + visible. </td> + </tr> + <tr> + <td>{@link android.widget.ViewFlipper ViewFlipper} </td> + <td>A list that displays one item at a time, inside a one-row textbox. It + can be set to swap items at timed intervals, like a slide show. </td> + </tr> + <tr> + <td>{@link android.widget.ViewSwitcher ViewSwitcher} </td> + <td>Same as ViewFlipper. </td> + </tr> +</table> |