canvas.html

是MIDP 的API 查詢文件, 大家可以看一下裡面的index.html, 再用Package 或 Class 名字來查.

<DT><B>Parameters:</B><DD><CODE>keyCode</CODE> - the key code of the key that was repeated<DT><B>See Also: </B><DD><A HREF="../../../javax/microedition/lcdui/Canvas.html#hasRepeatEvents()"><CODE>hasRepeatEvents()</CODE></A></DL>
</DD>
</DL>
<HR>

<A NAME="keyReleased(int)"><!-- --></A><H3>
keyReleased</H3>
<PRE>
protected void <B>keyReleased</B>(int&nbsp;keyCode)</PRE>
<DL>
<DD>Called when a key is released.
 <P>
 The <code>getGameAction()</code> method can be called to
 determine what game action, if any, is mapped to the key.
 Class <code>Canvas</code> has an empty implementation of this method, and
 the subclass has to redefine it if it wants to listen this method.
 </P><DD><DL>
<DT><B>Parameters:</B><DD><CODE>keyCode</CODE> - the key code of the key that was released</DL>
</DD>
</DL>
<HR>

<A NAME="pointerPressed(int, int)"><!-- --></A><H3>
pointerPressed</H3>
<PRE>
protected void <B>pointerPressed</B>(int&nbsp;x,
                              int&nbsp;y)</PRE>
<DL>
<DD>Called when the pointer is pressed. 

 <P>
 The <A HREF="../../../javax/microedition/lcdui/Canvas.html#hasPointerEvents()"><CODE>hasPointerEvents()</CODE></A>
 method may be called to determine if the device supports pointer events.
 Class <code>Canvas</code> has an empty implementation of this method, and
 the subclass has to redefine it if it wants to listen this method.
 </P><DD><DL>
<DT><B>Parameters:</B><DD><CODE>x</CODE> - the horizontal location where the pointer was pressed (relative
 to the <code>Canvas</code>)<DD><CODE>y</CODE> - the vertical location where the pointer was pressed
 (relative to the <code>Canvas</code>)</DL>
</DD>
</DL>
<HR>

<A NAME="pointerReleased(int, int)"><!-- --></A><H3>
pointerReleased</H3>
<PRE>
protected void <B>pointerReleased</B>(int&nbsp;x,
                               int&nbsp;y)</PRE>
<DL>
<DD>Called when the pointer is released. 

 <P>
 The <A HREF="../../../javax/microedition/lcdui/Canvas.html#hasPointerEvents()"><CODE>hasPointerEvents()</CODE></A>
 method may be called to determine if the device supports pointer events.
 Class <code>Canvas</code> has an empty implementation of this method, and
 the subclass has to redefine it if it wants to listen this method.
 </P><DD><DL>
<DT><B>Parameters:</B><DD><CODE>x</CODE> - the horizontal location where the pointer was released
 (relative to the <code>Canvas</code>)<DD><CODE>y</CODE> - the vertical location where the pointer was released
 (relative to the <code>Canvas</code>)</DL>
</DD>
</DL>
<HR>

<A NAME="pointerDragged(int, int)"><!-- --></A><H3>
pointerDragged</H3>
<PRE>
protected void <B>pointerDragged</B>(int&nbsp;x,
                              int&nbsp;y)</PRE>
<DL>
<DD>Called when the pointer is dragged.

 <P>
 The <A HREF="../../../javax/microedition/lcdui/Canvas.html#hasPointerMotionEvents()"><CODE>hasPointerMotionEvents()</CODE></A>
 method may be called to determine if the device supports pointer events.
 Class <code>Canvas</code> has an empty implementation of this method, and
 the subclass has to redefine it if it wants to listen this method.
 </P><DD><DL>
<DT><B>Parameters:</B><DD><CODE>x</CODE> - the horizontal location where the pointer was dragged
 (relative to the <code>Canvas</code>)<DD><CODE>y</CODE> - the vertical location where the pointer was dragged
 (relative to the <code>Canvas</code>)</DL>
</DD>
</DL>
<HR>

<A NAME="repaint(int, int, int, int)"><!-- --></A><H3>
repaint</H3>
<PRE>
public final void <B>repaint</B>(int&nbsp;x,
                          int&nbsp;y,
                          int&nbsp;width,
                          int&nbsp;height)</PRE>
<DL>
<DD>Requests a repaint for the specified region of the
 <code>Canvas</code>. Calling
 this method may result in subsequent call to
 <code>paint()</code>, where the passed
 <code>Graphics</code> object's clip region will include at
 least the specified
 region.

 <p> If the canvas is not visible, or if width and height are zero or 
 less, or if the rectangle does not specify a visible region of 
 the display, this call has no effect. </p>

 <p> The call to <code>paint()</code> occurs asynchronously of
 the call to <code>repaint()</code>.
 That is, <code>repaint()</code> will not block waiting for
 <code>paint()</code> to finish. The
 <code>paint()</code> method will either be called after the
 caller of <code>repaint(</code>)
 returns
 to the implementation (if the caller is a callback) or on another thread
 entirely. </p>

 <p> To synchronize with its <code>paint()</code> routine,
 applications can use either
 <A HREF="../../../javax/microedition/lcdui/Display.html#callSerially(java.lang.Runnable)"><CODE>Display.callSerially()</CODE></A> or
 <A HREF="../../../javax/microedition/lcdui/Canvas.html#serviceRepaints()"><CODE>serviceRepaints()</CODE></A>, or they can code explicit
 synchronization into their <code>paint()</code> routine. </p>

 <p> The origin of the coordinate system is above and to the left of the
 pixel in the upper left corner of the displayable area of the
 <code>Canvas</code>.
 The X-coordinate is positive right and the Y-coordinate is 
 positive downwards.
 </p><DD><DL>
<DT><B>Parameters:</B><DD><CODE>x</CODE> - the x coordinate of the rectangle to be repainted<DD><CODE>y</CODE> - the y coordinate of the rectangle to be repainted<DD><CODE>width</CODE> - the width of the rectangle to be repainted<DD><CODE>height</CODE> - the height of the rectangle to be repainted<DT><B>See Also: </B><DD><A HREF="../../../javax/microedition/lcdui/Display.html#callSerially(java.lang.Runnable)"><CODE>Display.callSerially(Runnable)</CODE></A>, 
<A HREF="../../../javax/microedition/lcdui/Canvas.html#serviceRepaints()"><CODE>serviceRepaints()</CODE></A></DL>
</DD>
</DL>
<HR>

<A NAME="repaint()"><!-- --></A><H3>
repaint</H3>
<PRE>
public final void <B>repaint</B>()</PRE>
<DL>
<DD>Requests a repaint for the entire <code>Canvas</code>. The
 effect is identical to
 <p> <code> repaint(0, 0, getWidth(), getHeight()); </code></DL>
<HR>

<A NAME="serviceRepaints()"><!-- --></A><H3>
serviceRepaints</H3>
<PRE>
public final void <B>serviceRepaints</B>()</PRE>
<DL>
<DD>Forces any pending repaint requests to be serviced immediately. This
 method blocks until the pending requests have been serviced. If 
 there are
 no pending repaints, or if this canvas is not visible on the display,
 this call does nothing and returns immediately. 

 <p><strong>Warning:</strong> This method blocks until the call to the
 application's <code>paint()</code> method returns. The
 application has no
 control over
 which thread calls <code>paint()</code>; it may vary from
 implementation to
 implementation. If the caller of <code>serviceRepaints()</code>
 holds a lock that the
 <code>paint()</code> method acquires, this may result in
 deadlock. Therefore, callers
 of <code>serviceRepaints()</code> <em>must not</em> hold any
 locks that might be
 acquired within the <code>paint()</code> method. The
 <A HREF="../../../javax/microedition/lcdui/Display.html#callSerially(java.lang.Runnable)"><CODE>Display.callSerially()</CODE></A>
 method provides a facility where an application can be called back after
 painting has completed, avoiding the danger of deadlock.
 </p><DD><DL>
<DT><B>See Also: </B><DD><A HREF="../../../javax/microedition/lcdui/Display.html#callSerially(java.lang.Runnable)"><CODE>Display.callSerially(Runnable)</CODE></A></DL>
</DD>
</DL>
<HR>

<A NAME="showNotify()"><!-- --></A><H3>
showNotify</H3>
<PRE>
protected void <B>showNotify</B>()</PRE>
<DL>
<DD>The implementation calls <code>showNotify()</code>
 immediately prior to this <code>Canvas</code> being made
 visible on the display.
 Canvas subclasses may override
 this method to perform tasks before being shown, such
 as setting up animations, starting timers, etc.
 The default implementation of this method in class
 <code>Canvas</code> is empty.</DL>
<HR>

<A NAME="hideNotify()"><!-- --></A><H3>
hideNotify</H3>
<PRE>
protected void <B>hideNotify</B>()</PRE>
<DL>
<DD>The implementation calls <code>hideNotify()</code> shortly
 after the <code>Canvas</code> has been
 removed from the display.
 <code>Canvas</code> subclasses may override this method in
 order to pause
 animations, 
 revoke timers, etc.  The default implementation of this 
 method in class <code>Canvas</code> is empty.</DL>
<HR>

<A NAME="paint(javax.microedition.lcdui.Graphics)"><!-- --></A><H3>
paint</H3>
<PRE>
protected abstract void <B>paint</B>(<A HREF="../../../javax/microedition/lcdui/Graphics.html">Graphics</A>&nbsp;g)</PRE>
<DL>
<DD>Renders the <code>Canvas</code>. The application must implement
 this method in
 order to paint any graphics.

 <p>The <code>Graphics</code> object's clip region defines the
 area of the screen
 that is considered to be invalid. A correctly-written
 <code>paint()</code> routine
 must paint <em>every</em> pixel within this region. This is necessary
 because the implementation is not required to clear the region prior to
 calling <code>paint()</code> on it.  Thus, failing to paint
 every pixel may result
 in a portion of the previous screen image remaining visible. </p>

 <p>Applications <em>must not</em> assume that
 they know the underlying source of the <code>paint()</code>
 call and use this
 assumption
 to paint only a subset of the pixels within the clip region. The 
 reason is
 that this particular <code>paint()</code> call may have
 resulted from multiple
 <code>repaint()</code>
 requests, some of which may have been generated from outside the
 application. An application that paints only what it thinks is 
 necessary to
 be painted may display incorrectly if the screen contents had been
 invalidated by, for example, an incoming telephone call. </p>

 <p>Operations on this graphics object after the <code>paint()
 </code>call returns are
 undefined. Thus, the application <em>must not</em> cache this
 <code>Graphics</code>
 object for later use or use by another thread. It must only be 
 used within
 the scope of this method. </p>

 <p>The implementation may postpone visible effects of
 graphics operations until the end of the paint method.</p>

 <p> The contents of the <code>Canvas</code> are never saved if
 it is hidden and then
 is made visible again. Thus, shortly after
 <code>showNotify()</code> is called,
 <code>paint()</code> will always be called with a
 <code>Graphics</code> object whose clip region
 specifies the entire displayable area of the
 <code>Canvas</code>.  Applications
 <em>must not</em> rely on any contents being preserved from a previous
 occasion when the <code>Canvas</code> was current. This call to
 <code>paint()</code> will not
 necessarily occur before any other key or pointer
 methods are called on the <code>Canvas</code>.  Applications
 whose repaint
 recomputation is expensive may create an offscreen
 <code>Image</code>, paint into it,
 and then draw this image on the <code>Canvas</code> when
 <code>paint()</code> is called. </p>

 <P>The application code must never call <code>paint()</code>;
 it is called only by
 the implementation.</P>

 <P>The <code>Graphics</code> object passed to the
 <code>paint()</code> method has the following
 properties:</P>
 <UL>
 <LI>the destination is the actual display, or if double buffering is in 
 effect, a back buffer for the display;</LI>
 <LI>the clip region includes at least one pixel
 within this <code>Canvas</code>;</LI>
 <LI>the current color is black;</LI>
 <LI>the font is the same as the font returned by
 <A HREF="../../../javax/microedition/lcdui/Font.html#getDefaultFont()"><CODE>Font.getDefaultFont()</CODE></A>;</LI>
 <LI>the stroke style is <A HREF="../../../javax/microedition/lcdui/Graphics.html#SOLID"><CODE>SOLID</CODE></A>;</LI>
 <LI>the origin of the coordinate system is located at the upper-left
 corner of the <code>Canvas</code>; and</LI>
 <LI>the <code>Canvas</code> is visible, that is, a call to
 <code>isShown()</code> will return
 <code>true</code>.</LI>
 </UL><DD><DL>
<DT><B>Parameters:</B><DD><CODE>g</CODE> - the <code>Graphics</code> object to be used for
 rendering the <code>Canvas</code></DL>
</DD>
</DL>
<HR>

<A NAME="sizeChanged(int, int)"><!-- -