📄 item.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN""http://www.w3.org/TR/REC-html40/frameset.dtd">
<!--NewPage-->
<HTML>
<HEAD>
<!-- Generated by javadoc on Wed Sep 24 14:57:49 PDT 2003 -->
<TITLE>
MID Profile: Class Item
</TITLE>
<LINK REL ="stylesheet" TYPE="text/css" HREF="../../../stylesheet.css" TITLE="Style">
</HEAD>
<BODY BGCOLOR="white">
<!-- ========== START OF NAVBAR ========== -->
<A NAME="navbar_top"><!-- --></A><TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0">
<TR>
<TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1">
<A NAME="navbar_top_firstrow"><!-- --></A><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3">
<TR ALIGN="center" VALIGN="top">
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD>
<TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="class-use/Item.html"><FONT CLASS="NavBarFont1"><B>Use</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../index-all.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD>
</TR>
</TABLE>
</TD>
<TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM>
<strong>MID Profile</strong></EM>
</TD>
</TR>
<TR>
<TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2">
<A HREF="../../../javax/microedition/lcdui/ImageItem.html"><B>PREV CLASS</B></A>
<A HREF="../../../javax/microedition/lcdui/List.html"><B>NEXT CLASS</B></A></FONT></TD>
<TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2">
<A HREF="../../../index.html" TARGET="_top"><B>FRAMES</B></A>
<A HREF="Item.html" TARGET="_top"><B>NO FRAMES</B></A></FONT></TD>
</TR>
<TR>
<TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">
SUMMARY: INNER | <A HREF="#field_summary">FIELD</A> | CONSTR | <A HREF="#method_summary">METHOD</A></FONT></TD>
<TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">
DETAIL: <A HREF="#field_detail">FIELD</A> | CONSTR | <A HREF="#method_detail">METHOD</A></FONT></TD>
</TR>
</TABLE>
<!-- =========== END OF NAVBAR =========== -->
<HR>
<!-- ======== START OF CLASS DATA ======== -->
<H2>
<FONT SIZE="-1">
javax.microedition.lcdui</FONT>
<BR>
Class Item</H2>
<PRE>
<A HREF="../../../java/lang/Object.html">java.lang.Object</A>
|
+--<B>javax.microedition.lcdui.Item</B>
</PRE>
<DL>
<DT><B>Direct Known Subclasses:</B> <DD><A HREF="../../../javax/microedition/lcdui/ChoiceGroup.html">ChoiceGroup</A>, <A HREF="../../../javax/microedition/lcdui/CustomItem.html">CustomItem</A>, <A HREF="../../../javax/microedition/lcdui/DateField.html">DateField</A>, <A HREF="../../../javax/microedition/lcdui/Gauge.html">Gauge</A>, <A HREF="../../../javax/microedition/lcdui/ImageItem.html">ImageItem</A>, <A HREF="../../../javax/microedition/lcdui/Spacer.html">Spacer</A>, <A HREF="../../../javax/microedition/lcdui/StringItem.html">StringItem</A>, <A HREF="../../../javax/microedition/lcdui/TextField.html">TextField</A></DD>
</DL>
<HR>
<DL>
<DT>public abstract class <B>Item</B><DT>extends <A HREF="../../../java/lang/Object.html">Object</A></DL>
<P>
A superclass for components that can be added to a <A HREF="../../../javax/microedition/lcdui/Form.html"><CODE>Form</CODE></A>. All <code>Item</code> objects have a label field, which is a string that is attached to the item. The label is typically displayed near the component when it is displayed within a screen. The label should be positioned on the same horizontal row as the item or directly above the item. The implementation should attempt to distinguish label strings from other textual content, possibly by displaying the label in a different font, aligning it to a different margin, or appending a colon to it if it is placed on the same line as other string content. If the screen is scrolling, the implementation should try to keep the label visible at the same time as the <code>Item</code>. <p>In some cases, when the user attempts to interact with an <code>Item</code>, the system will switch to a system-generated screen where the actual interaction takes place. If this occurs, the label will generally be carried along and displayed within this new screen in order to provide the user with some context for the operation. For this reason it is recommended that applications supply a label to all interactive Item objects. However, this is not required, and a <code>null</code> value for a label is legal and specifies the absence of a label. </p> <h3>Item Layout</h3> <p>An <code>Item's</code> layout within its container is influenced through layout directives:</p> <ul> <li> <code>LAYOUT_DEFAULT</code> </li> <li> <code>LAYOUT_LEFT</code> </li> <li> <code>LAYOUT_RIGHT</code> </li> <li> <code>LAYOUT_CENTER</code> </li> <li> <code>LAYOUT_TOP</code> </li> <li> <code>LAYOUT_BOTTOM</code> </li> <li> <code>LAYOUT_VCENTER</code> </li> <li> <code>LAYOUT_NEWLINE_BEFORE</code> </li> <li> <code>LAYOUT_NEWLINE_AFTER</code> </li> <li> <code>LAYOUT_SHRINK</code> </li> <li> <code>LAYOUT_VSHRINK</code> </li> <li> <code>LAYOUT_EXPAND</code> </li> <li> <code>LAYOUT_VEXPAND</code> </li> <li> <code>LAYOUT_2</code> </li> </ul> <p>The <code>LAYOUT_DEFAULT</code> directive indicates that the container's default layout policy is to be used for this item. <code>LAYOUT_DEFAULT</code> has the value zero and has no effect when combined with other layout directives. It is useful within programs in order to document the programmer's intent.</p> <p>The <code>LAYOUT_LEFT</code>, <code>LAYOUT_RIGHT</code>, and <code>LAYOUT_CENTER</code> directives indicate horizontal alignment and are mutually exclusive. Similarly, the <code>LAYOUT_TOP</code>, <code>LAYOUT_BOTTOM</code>, and <code>LAYOUT_VCENTER</code> directives indicate vertical alignment and are mutually exclusive.</p> <p>A horizontal alignment directive, a vertical alignment directive, and any combination of other layout directives may be combined using the bit-wise <code>OR</code> operator (<code>|</code>) to compose a layout directive value. Such a value is used as the parameter to the <A HREF="../../../javax/microedition/lcdui/Item.html#setLayout(int)"><CODE>setLayout(int)</CODE></A> method and is the return value from the <A HREF="../../../javax/microedition/lcdui/Item.html#getLayout()"><CODE>getLayout()</CODE></A> method.</p> <p>Some directives have no defined behavior in some contexts. A layout directive is ignored if its behavior is not defined for the particular context within which the <code>Item</code> resides.</p> <p>A complete specification of the layout of <code>Items</code> within a <code>Form</code> is given <a href="Form.html#layout">here</a>.</p> <a name="sizes"></a> <h3>Item Sizes</h3> <p><code>Items</code> have two explicit size concepts: the <em>minimum</em> size and the <em>preferred</em> size. Both the minimum and the preferred sizes refer to the total area of the <code>Item</code>, which includes space for the <code>Item's</code> contents, the <code>Item's</code> label, as well as other space that is significant to the layout policy. These sizes do not include space that is not significant for layout purposes. For example, if the addition of a label to an <code>Item</code> would cause other <code>Items</code> to move in order to make room, then the space occupied by this label is significant to layout and is counted as part of the <code>Item's</code> minimum and preferred sizes. However, if an implementation were to place the label in a margin area reserved exclusively for labels, this would not affect the layout of neighboring <code>Items</code>. In this case, the space occupied by the label would not be considered part of the minimum and preferred sizes.</p> <p>The minimum size is the smallest size at which the <code>Item</code> can function and display its contents, though perhaps not optimally. The minimum size may be recomputed whenever the <code>Item's</code> contents changes.</p> <p>The preferred size is generally a size based on the <code>Item's</code> contents and is the smallest size at which no information is clipped and text wrapping (if any) is kept to a tolerable minimum. The preferred size may be recomputed whenever the <code>Item's</code> contents changes. The application can <em>lock</em> the preferred width or preferred height (or both) by supplying specific values for parameters to the <A HREF="../../../javax/microedition/lcdui/Item.html#setPreferredSize(int, int)"><CODE>setPreferredSize</CODE></A> method. The manner in which an <code>Item</code> fits its contents within an application-specified preferred size is implementation-specific. However, it is recommended that textual content be word-wrapped to fit the preferred size set by the application. The application can <em>unlock</em> either or both dimensions by supplying the value <code>-1</code> for parameters to the <code>setPreferredSize</code> method.</p> <p>When an <code>Item</code> is created, both the preferred width and height are unlocked. In this state, the implementation computes the preferred width and height based on the <code>Item's</code> contents, possibly including other relevant factors such as the <code>Item's</code> graphic design and the screen dimensions. After having locked either the preferred width or height, the application can restore the initial, unlocked state by calling <code>setPreferredSize(-1, -1)</code>.</p> <p>The application can lock one dimension of the preferred size and leave the other unlocked. This causes the system to compute an appropriate value for the unlocked dimension based on arranging the contents to fit the locked dimension. If the contents changes, the size on the unlocked dimension is recomputed to reflect the new contents, but the size on the locked dimension remains unchanged. For example, if the application called <code>setPreferredSize(50, -1)</code>, the preferred width would be locked at <code>50</code> pixels and the preferred height would be computed based on the <code>Item's</code> contents. Similarly, if the application called <code>setPreferredSize(-1, 60)</code>, the preferred height would be locked at <code>60</code> pixels and the preferred width would be computed based on the <code>Item's</code> contents. This feature is particularly useful for <code>Items</code> with textual content that can be line wrapped.</p> <p>The application can also lock both the preferred width and height to specific values. The <code>Item's</code> contents are truncated or padded as necessary to honor this request. For <code>Items</code> containing text, the text should be wrapped to the specified width, and any truncation should occur at the end of the text.</p> <p><code>Items</code> also have an implicit maximum size provided by the implementation. The maximum width is typically based on the width of the screen space available to a <code>Form</code>. Since <code>Forms</code> can scroll vertically, the maximum height should typically not be based on the height of the available screen space.</p> <p>If the application attempts to lock a preferred size dimension to a value smaller than the minimum or larger than the maximum, the implementation may disregard the requested value and instead use either the minimum or maximum as appropriate. If this occurs, the actual values used must be visible to the application via the values returned from the <A HREF="../../../javax/microedition/lcdui/Item.html#getPreferredWidth()"><CODE>getPreferredWidth</CODE></A> and <A HREF="../../../javax/microedition/lcdui/Item.html#getPreferredHeight()"><CODE>getPreferredHeight</CODE></A> methods. </p> <h3>Commands</h3> <p>A <code>Command</code> is said to be present on an <code>Item</code> if the <code>Command</code> has been added to this <code>Item</code> with a prior call to <A HREF="../../../javax/microedition/lcdui/Item.html#addCommand(javax.microedition.lcdui.Command)"><CODE>addCommand(javax.microedition.lcdui.Command)</CODE></A> or <A HREF="../../../javax/microedition/lcdui/Item.html#setDefaultCommand(javax.microedition.lcdui.Command)"><CODE>setDefaultCommand(javax.microedition.lcdui.Command)</CODE></A> and if the <code>Command</code> has not been removed with a subsequent call to <A HREF="../../../javax/microedition/lcdui/Item.html#removeCommand(javax.microedition.lcdui.Command)"><CODE>removeCommand(javax.microedition.lcdui.Command)</CODE></A>. <code>Commands</code> present on an item should have a command type of <code>ITEM</code>. However, it is not an error for a command whose type is other than <code>ITEM</code> to be added to an item. For purposes of presentation and placement within its user interface, the implementation is allowed to treat a command's items as if they were of type <code>ITEM</code>. </p> <p><code>Items</code> may have a <em>default</em> <code>Command</code>. This state is controlled by the <A HREF="../../../javax/microedition/lcdui/Item.html#setDefaultCommand(javax.microedition.lcdui.Command)"><CODE>setDefaultCommand(javax.microedition.lcdui.Command)</CODE></A> method. The default <code>Command</code> is eligible to be bound to a special platform-dependent user gesture. The implementation chooses which gesture is the most appropriate to initiate the default command on that particular <code>Item</code>. For example, on a device that has a dedicated selection key, pressing this key might invoke the item's default command. Or, on a stylus-based device, tapping on the <code>Item</code> might invoke its default command. Even if it can be invoked through a special gesture, the default command should also be invokable in the same fashion as other item commands.</p> <p>It is possible that on some devices there is no special gesture suitable for invoking the default command on an item. In this case the default command must be accessible to the user in the same fashion as other item commands. The implementation may use the state of a command being the default in deciding where to place the command in its user interface.</p> <p>It is possible for an <code>Item</code> not to have a default command. In this case, the implementation may bind its special user gesture (if any) for another purpose, such as for displaying a menu of commands. The default state of an <code>Item</code> is not to have a default command. An <code>Item</code> may be set to have no default <code>Command</code> by removing it from the <code>Item</code> or by passing <code>null</code> to the <code>setDefaultCommand()</code> method.</p> <p>The same command may occur on more than one <code>Item</code> and also on more than one <code>Displayable</code>. If this situation occurs, the user must be provided with distinct gestures to invoke that command on each <code>Item</code> or <code>Displayable</code> on which it occurs, while those <code>Items</code> or <code>Displayables</code> are visible on the display. When the user invokes the command, the listener (<code>CommandListener</code> or <code>ItemCommandListener</code> as appropriate) of just the object on which the command was invoked will be called.</p> <p>Adding commands to an <code>Item</code> may affect its appearance, the way it is laid out, and the traversal behavior. For example, the presence of commands on an <code>Item</code> may cause row breaks to occur, or it may cause additional graphical elements (such as a menu icon) to appear. In particular, if a <code>StringItem</code> whose appearance mode is <code>PLAIN</code> (see below) is given one or more <code>Commands</code>, the implementation is allowed to treat it as if it had a different appearance mode.</p> <a name="appearance"></a> <h3>Appearance Modes</h3> <p>The <code>StringItem</code> and <code>ImageItem</code> classes have an <em>appearance mode</em> attribute that can be set in their constructors. This attribute can have one of the values <A HREF="../../../javax/microedition/lcdui/Item.html#PLAIN"><CODE>PLAIN</CODE></A>, <A HREF="../../../javax/microedition/lcdui/Item.html#HYPERLINK"><CODE>HYPERLINK</CODE></A>, or <A HREF="../../../javax/microedition/lcdui/Item.html#BUTTON"><CODE>BUTTON</CODE></A>. An appearance mode of <code>PLAIN</code> is typically used for non-interactive display of textual or graphical material. The appearance mode values do not have any side effects on the interactivity of the item. In order to be interactive, the item must have one or more <code>Commands</code> (preferably with a default command assigned), and it must have a <code>CommandListener</code> that receives notification of <code>Command</code> invocations. The appearance mode values also do not have any effect on the semantics of <code>Command</code> invocation on the item. For example, setting the appearance mode of a <code>StringItem</code> to be <code>HYPERLINK</code> requests that the implementation display the string contents as if they were a hyperlink in a browser. It is the application's responsibility to attach a <code>Command</code> and a listener to the <code>StringItem</code> that provide behaviors that the user would expect from invoking⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -