ch5.htm

JAVA Developing Professional JavaApplets

   if ((currentRow < numRows) && (currentCol
&lt; numColumns)) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp; // See if it fits in the column...<BR>
&nbsp;&nbsp;&nbsp;&nbsp; if ((xHit &gt;= x) &amp;&amp; (xHit &lt;
(x + cellWidth))) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//
See if it fits in the row...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if
((yHit &gt;= y) &amp;&amp; (yHit &lt; (y + cellHeight))) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;paintIndex
= index;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;paintX
= x;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;paintY
= y;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return
matrix[index];<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}
// end if<BR>
&nbsp;&nbsp;&nbsp;&nbsp; } // end if<BR>
&nbsp;&nbsp;&nbsp;} // end inner if<BR>
&nbsp;&nbsp;} // end else<BR>
&nbsp;&nbsp;// Adjust column display of cells<BR>
&nbsp;&nbsp;if (j == 0)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;currentCol = leftCell;
<BR>
&nbsp;&nbsp;else<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;++currentCol;
<BR>
 }&nbsp;&nbsp;// end column for<BR>
 // Now start data cells at appropriate top...<BR>
 if (i == 0)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; currentRow = topCell;<BR>
 else<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;++currentRow;<BR>
 } // end row for<BR>
 return null;&nbsp;&nbsp;// Only used if paint is false...<BR>
}</TT>
</BLOCKQUOTE>
<HR>
<P>
The painting begins with the <TT>update()</TT>
method. Recall that the earlier versions of the spreadsheet applet
have a brief flicker of white when the spreadsheet area is repainted.
This is because the <TT>update()</TT>
method, by default, clears out the area before the <TT>paint()</TT>
area is called; this clearing results in the flicker, which can
be solved by overriding the <TT>update()</TT>
method. In this case, it calls the <TT>paint()</TT>
method directly. This method, in turn, calls the <TT>calculatePaint()</TT>
method.
<P>
The <TT>calculatePaint()</TT> method
is at the heart of the SpreadsheetContainer class. It is not only
used for painting, but also is called by other routines to calculate
where a cell is located. The second parameter of <TT>calculatePaint()</TT>
indicates whether the method should repaint the region or simply
calculate a value. The first part of the method calculates how
many rows and columns of SpreadsheetCells can be displayed in
the current canvas area. The <TT>size()</TT>
method returns the area's size, and the <TT>getFontMetrics()</TT>
methods are used to calculate the cell dimensions. Note that the
dimensions will change when the font of the spreadsheet is resized,
as discussed in the previous chapter's section on fonts.
<P>
The next step is to loop through all the rows and columns to be
displayed. The <TT>currentRow</TT>
and <TT>currentCol</TT> variables
indicate which SpreadsheetCell is to be painted. These values
are initially set to <TT>0</TT> so
that the row and column headers are displayed. At the bottom of
the <TT>for</TT> loops, these are
adjusted to the top cell or leftmost column. In the ensuing iterations,
the variables are simply incremented to get the new row or column.
<P>
If the mode of the <TT>calculatePaint()</TT>
method is true, then the cells are to be painted. In this case,
the code checks to see whether the item falls in the clipping
rectangle, retrieved by the <TT>getClipRect()</TT>
method. This actually represents the area to be painted. The clipping
rectangle could be the whole screen or a single cell. The code
that sets a highlighted cell or marks an area (to be discussed)
only forces the area affected to be repainted. If it does fall
in the region, the individual SpreadsheetCell is painted at the
current coordinates. Recall that the cell has colors and a font
associated with it. Highlighting or marking a cell is really nothing
more than changing a SpreadsheetCell object's internal color variables
and forcing it to be repainted. See the <A HREF="ch3.htm" >Chapter 3</A>,
&quot;Building a Spreadsheet Applet,&quot; tutorial for how the
SpreadsheetCell class works.
<P>
Painting affects only those objects that fall in the clipping
rectangle. The <TT>intersects()</TT>
method is used to see whether two Rectangle objects overlap. By
painting only the cells that intersect the clipping region, the
code saves some unnecessary processing.
<P>
If the method is not in painting mode, then the processing is
used to check which cell an x-y coordinate belongs to. This is
useful when the user clicks on a cell to be highlighted and when
marking occurs.
<P>
By using a central routine for determining the locations of SpreadsheetCells,
such activities as painting, scrolling, marking, and highlighting
become relatively easy. If something goes wrong, it probably could
be traced back to the <TT>calculatePaint()</TT>
method.
<H2><A NAME="MarkingCells"><FONT SIZE=5 COLOR=#FF0000>Marking
Cells</FONT></A></H2>
<P>
It is useful to mark cells to indicate that they are subject to
some upcoming operation, such as cutting or copying, or, in this
case, producing a graph. Marking is performed in this applet by
clicking on a valid cell, holding the mouse key down, and dragging
in a southeasterly direction. When the mouse is released, marking
is complete. Figure 5.2 shows what a spreadsheet with some cells
marked looks like.
<P>
<A HREF="f5-2.gif" ><B>Figure 5.2 :</B><I> A spreadsheet with cells marked.</I></A>
<P>
Marking cells is actually a simple extension of the techniques
that have been developed through the last three chapters. There
are three key aspects to marking: tracking mouse movements, keeping
track of the cells selected, and changing the color of the marked
cells.
<P>
To track mouse movements, the SpreadsheetContainer <TT>handleEvent()</TT>
method is modified to manage the mouse actions. The modified code
is detailed in Listing 5.3.
<HR>
<BLOCKQUOTE>
<B>Listing 5.3. SpreadsheetContainer event handler.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT>public boolean handleEvent(Event evt)
{<BR>
&nbsp;switch(evt.id) {<BR>
&nbsp;&nbsp;// Mouse clicks. See whether you should highlight
<BR>
&nbsp;&nbsp;// cell on spreadsheet...<BR>
&nbsp;&nbsp;case Event.MOUSE_DOWN:<BR>
&nbsp;&nbsp;&nbsp;&nbsp;setMouseHighlight(evt.x,evt.y);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;// Handle cell marking...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;toggleMarking(evt.x,evt.y);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;return false;<BR>
&nbsp;case Event.MOUSE_DRAG:<BR>
&nbsp;&nbsp;// Select cells if marking...<BR>
&nbsp;&nbsp;dragMarking(evt.x,evt.y);<BR>
&nbsp;&nbsp;return false;<BR>
&nbsp;case Event.MOUSE_UP:<BR>
&nbsp;&nbsp;// If marking, then you are done!<BR>
&nbsp;&nbsp;stopMarking(evt.x,evt.y);<BR>
&nbsp;&nbsp;return false;<BR>
&nbsp;}<BR>
&nbsp;default:<BR>
&nbsp;&nbsp;return false;<BR>
&nbsp;}<BR>
}</TT>
</BLOCKQUOTE>
<HR>
<P>
The marking code is too long and involved to list here; refer
to the CD-ROM for the complete code. However, the general approach
and highlights can be presented.
<P>
When you click the mouse over a valid cell (not a row or column
header), the cell becomes the current focus and is highlighted.
This is done through the <TT>setMouseHighlight()</TT>
method, which calls <TT>calculatePaint()</TT>
to find the reference of the selected SpreadsheetCell. After the
cell is highlighted, the <TT>toggleMarking()</TT>
method is called to either begin marking or to reset the marking
if there were cells selected at the time of the mouse click. The
<TT>startMarking()</TT> method begins
tracking the mouse, and <TT>resetMarking()</TT>
resets the marking state. SpreadsheetCell objects are set to their
default colors through the <TT>setNewColors()</TT>
method, which is used to set the normal and highlighted values
of the spreadsheet. This method is called by the color dialog
discussed in the previous chapter, and is called here with the
current normal and highlighted colors as a simple way of resetting
colors.
<P>
As the mouse is being dragged (which means the mouse key is still
down), <TT>MOUSE_DRAG</TT> events
are issued. If marking is on, the <TT>dragMarking()</TT>
method checks to see whether the mouse has left the current cell;
if it has, then new cells are marked. The <TT>paintMarked()</TT>
method looks at the first cell marked and the last cell marked
and figures out the rectangular area to be painted. It then sets
the colors of each of the cells that are marked. The method then
forces a limited repaint of the SpreadsheetContainer so that painting
occurs quickly. The following code from <TT>paintMarked()</TT>
takes the top-left and bottom-right areas that are marked and
forces them to be repainted:
<BLOCKQUOTE>
<TT>repaint(startX,startY,endX-startX,endY-startY);</TT>
</BLOCKQUOTE>
<P>
When the paint message is processed, the marked cells are drawn
in their new color. Cells outside the clipping rectangle issued
by the <TT>repaint()</TT> method are
not drawn.
<P>
When the mouse is released, the <TT>stopMarking()</TT>
method is called, and the marking is finished. The marked areas
can then be used for further operations.
<H2><A NAME="DrawingGraphs"><FONT SIZE=5 COLOR=#FF0000>Drawing
Graphs</FONT></A></H2>
<P>
The last feature of the spreadsheet applet to be developed is
drawing graphs from the marked cells. Most of the work is done
in the <TT>graphCanvas()</TT> class.
However, the graph is displayed inside a dialog object based on
the GraphDialog class.
<P>
Two spreadsheet applets can produce two types of graphs: a line
graph and a bar chart. The latter is shown in Figure 5.3. They
are invoked by new menu items off the SpreadsheetFrame object.
The menu items result in a call to the SpreadsheetFrame method
<TT>launchGraphicsDialog()</TT>, which
gets the currently marked data and then displays the graphics
dialog box (which was instantiated in the frame's constructor).
If nothing is marked, an error message in the status bar indicates
that nothing was drawn.
<P>
<A HREF="f5-3.gif" ><B>Figure 5.3 :</B> <I>Spreadsheet applet bar chart.</I></A>
<P>
The GraphData class is an accessor class used to store the data
to be displayed. It contains an array of double values representing
the data to be plotted and an array of Strings used as the column
labels. These arrays are prepared in the SpreadsheetContainer
method <TT>getGraphData()</TT>, which
is called by the frame's <TT>launchGraphicsDialog()</TT>
method just discussed. The <TT>getGraphData()</TT>
checks to see whether something is marked; if not, an IllegalArgumentException
object is thrown. Otherwise, it stores the marked data in the
GraphData object by moving across the columns. The bottom row
marked is used to generate the data to be plotted and is placed
in the double array. The top row is used to represent the column
String headers. If only one row is marked, the cell headers (A1,
A2, and so forth) are used as the column headers. The middle rows
that are marked are ignored. As a further exercise, you can modify
the graph-<BR>
plotting algorithms to support multiple rows of data.
<P>
Once the graph data is collected, the GraphDialog is displayed.
The dialog box is very simple, consisting of only two components:
the GraphCanvas object for drawing the graph and a button for
shutting down the dialog box. The only interesting code in the
dialog box involves resizing the dialog box to take up most of
the screen.
<BLOCKQUOTE>
<TT>// Get the screen dimensions...<BR>
Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
<BR>
// Get the font and use to calculate some margins...<BR>
FontMetrics fm = Toolkit.getDefaultToolkit().getFontMetrics(getFont());
<BR>
resize(screen.width,screen.height - (4 * fm.getHeight()) );</TT>
</BLOCKQUOTE>
<P>
This code uses the AWT Toolkit to get the screen size and the
current font. The dialog box then resizes itself to take up the
screen's full width and most of its height.
<P>
When the dialog box is shown, it first calls the GraphCanvas <TT>prepareNewGraph()</TT>
method, which takes the GraphData and prepares it for presentation.
When the dialog box appears and a paint event is issued, the GraphCanvas
object draws the graph.
<P>
Listing 5.4 gives the full code for the GraphCanvas class. It
uses two constants to indicate the two graph modes it supports:
line or bar graph. When the canvas is constructed, it creates
an array of six Color objects. This array is used to randomly
generate colors for each bar chart or line so that they are more
easily distinguished. When the <TT>prepareNewGraph()</TT>
method is called, which must happen before painting occurs, the
maximum value is calculated and stored in the <TT>maxValue</TT>
variable. This is an important figure since it represents the
range of values the data is plotted against. The maximum value
is not the highest value in the data area, but actually is the
highest value rounded up to the nearest power of 10. Therefore,
if the top value is <TT>66</TT>, the
maximum value will be set to <TT>100</TT>.
Doing this makes it easy to divide the range of data values into
intervals of one-tenth the maximum. The data in Figure 5.3 shows
the plotting of values when the highest data value is <TT>66</TT>
and the range is set from <TT>0</TT>
to <TT>100</TT>.
<HR>
<BLOCKQUOTE>
<B>Listing 5.4. The GraphCanvas class.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT>// Not a public class.&nbsp;&nbsp;Imports
are in GraphDialog class<BR>
// This paints a graph on a canvas...<BR>
class GraphCanvas extends Canvas {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;// Types of graphs...<BR>
&nbsp;&nbsp;&nbsp;static final int LINE_GRAPH = 0;<BR>
&nbsp;&nbsp;&nbsp;static final int BAR_GRAPH = 1;<BR>