photocanvas.java

相册是J2me MIDLet 的一个demo程序

/*
 *  Filename: PhotoCanvas.java
 *  - contains definition of the class PhotoCanvas. It is a Canvas for image to be drawn on Canvas and to be shown to 
 *  user. Methods are defined to react to key and pointer actions on phone -  image scrolling and navigating forward 
 *	or backward within image album.
 *
 *  Application Name: Image Album Demo 
 *  Version: 2.0
 *  Release Date: 27th September, 2002
 *  Author:	Edmund Wong, Application Engineer, Metrowerks Hong Kong
 *
 *
 *  (c) Copyright. 2002. Metrowerks Corp. ALL RIGHTS RESERVED.
 *	This code is provided "AS IS" without warranty of any kind and subject to Metrowerks Sample Application
 *  End User License Agreement. NO EXTERNAL DISTRIBUTION OR COMMERCIALIZATION OF THE SOFTWARE IS PERMITTED 
 *  EXCEPT BY WRITTEN AGREEMENT OF METROWERKS."
 */

import javax.microedition.lcdui.*;
	
	
	/**
	 *  Create a class for implementing the Canvas for showing Images
	 */
	
	public class PhotoCanvas extends Canvas {
	
		/**
		 *  Create references  
		 */
		
		Image img;		// for image to be shown on Canvas
		
		String description;	//for description to be shown on Canvas
		
		int imageID;  // the imageID that will be shown to user as 'Image x of y', where x = imageID and y is the
					  // total no. of images in Album
		
		int imageByteSize;	// for showing size in byte of the image on Canvas when needed, used in displaying
							// downloaded image (i.e. when downloadImageCanvasFlag == true)
		
		ImageAlbum imageAlbumReference;	// for referencing the main object - ImageAlbum
			
		boolean downloadImageCanvasFlag; // = true if it is for displaying downloaded image, 
								  // = false if displaying images in the Album
								  
		Font font = null;	// get font object for checking the height of the fonts on Canvas
		
		
	    /**
		 *  Create variables for storing coordinates in pointer action for scrolling large images on screen 
		 */
		 
	    int pointerStartX;	// x-coordinate of the starting point of the pointer action
    	
    	int pointerStartY;	// y-coordinate of the starting point of the pointer action
    	
    	int originX;		// new origin's x-coordinate for origin translation
    	
    	int originY;		// new origin's y-coordinate for origin translation
    	
    	int stepX;			// storing the distance moved in x-direction during the pointer drag action
    	
    	int stepY;  		// storing the distance moved in y-direction during the pointer drag action
    	
    	int standardStepX;	// distance in x-direction that will be moved for each scroll in non-touch screen phone
    						// (i.e. when hasPointerEvents() == false)
    	
    	int standardStepY;  // distance in y-direction that will be moved for each scroll in non-touch screen phone
    						// (i.e. when hasPointerEvents() == false)
    	
	    
	   /**
     	* Constructor of PhotoCanvas
     	*/ 
     	
     	// constructor for use in creating PhotoCanvas for showing downloaded Image , with information of image size
     	// (in byte) passed
     	
     	PhotoCanvas(Image img, String description, int imageByteSize){
	
		this();
		
		this.img = img;
		
		this.description = description;
		
		this.imageByteSize = imageByteSize;
		
		downloadImageCanvasFlag = true;	// for indicating this is the Canvas for showing downloaded image
					
		}
     	
     	// constructor for use in creating PhotoCanvas for showing Images stored in Album
     	
		PhotoCanvas(Image img, String description, ImageAlbum imageAlbumReference){
	
		this();
		
		this.img = img;
		
		this.description = description;
		
		this.imageAlbumReference = imageAlbumReference;
		
		downloadImageCanvasFlag = false;	 // for indicating this is the Canvas for showing images in Album
					
		}
		
		PhotoCanvas(){
		
		originX = 0;
        
        originY = 0;
        
        standardStepX = getWidth()/4;	// setting default scrolling distance in x direction (for non-touch screen phone)
        
        standardStepY = getHeight()/4;	// setting default scrolling distance in y direction (for non-touch screen phone)
        
        font = Font.getDefaultFont();
        
		}
		
		
		/**
		 *  Draw the image onto the Canvas 
		 */
	
		public void paint(Graphics g) {
		
		g.setColor(255,255,255);	// fill in the background with white color
		
		g.fillRect(0,0,getWidth(),getHeight());
		
		g.translate(originX, originY);	 // translate the origin of graphics to the coordinates (originX, originY)
	    				
		g.setColor(0,0,0);			// set color to black to draw string 
		
				
			if (downloadImageCanvasFlag == false){		// Display no. of Images in Album if viewing images in Album
			
			g.drawImage(img, getWidth()/2, font.getHeight(), Graphics.TOP|Graphics.HCENTER);	//draw the image
			
			g.drawString(description, 5, 0, Graphics.TOP|Graphics.LEFT);
			
			g.drawString("Image " + imageID + " of " + ImageAlbum.totalImageNumber, 5, font.getHeight() + img.getHeight(), Graphics.TOP|Graphics.LEFT);
			
			} else {	// Display size of images when viewing downloaded images
			
			g.drawImage(img, getWidth()/2, font.getHeight()*2, Graphics.TOP|Graphics.HCENTER);	//draw the image with two row at top for string
							
			g.drawString("Choose Save Image to Save!", 5, 0, Graphics.TOP|Graphics.LEFT);
			
			g.drawString(description, 5, font.getHeight(), Graphics.TOP|Graphics.LEFT);	
			
			g.drawString("Image size: " + imageByteSize + " bytes", 5, font.getHeight()*2 + img.getHeight(), Graphics.TOP|Graphics.LEFT);
			
							
			}
			
		}	
		
		
		/**
		 *  Following methods provide functionality for user to scroll large image on screen for viewing the whole image,
		 *  and also browsing the images in the Album by navigating forward and backward using key action
		 *
		 *  
		 *	on touch screen phone: 
		 *
		 *	scroll to view large image -  by pointer drag action
		 *  
		 *  navigate to previous image - pressing navigation key UP or LEFT 
		 *
		 *  navigate to next image - pressing navigation key DOWN or RIGHT
		 *
		 *
		 *	on non-touch screen phone: 
		 *  
		 *	scroll to view large image - using navigation key UP,DOWN,LEFT,RIGHT
		 *
		 *	navigate to previous image - pressing KEYPAD KEY '1'
		 * 
		 *	navigate to next image - pressing KEYPAD KEY '3'
		 *  
		 */
		 
		 
		 
		/**
		 *  Method for responding to key action on phone 
		 */
		 
		protected void keyPressed(int keyCode) {
								
			// On A008\6288\388, Game Action LEFT and RIGHT keys are the UP and DOWN arrow keys on top 
			// of handset, while Game Action UP and DOWN keys are the UP and DOWN arrow keys on the left 
			// side of the handset.  
		    
			
			// keyPressed action for non-touch screen phone
			if (hasPointerEvents() == false) {
			
				// translate the origin of Graphics upon receiving navigation key action, distance translated = 
				// standardStep
			
				switch (getGameAction(keyCode)) {
		
				case UP:
		
				originY += standardStepY;
		
				repaint();
		
				break;
		
				case DOWN:
		
				originY -= standardStepY;
		
				repaint();
		
				break;
		
				case LEFT:
		
				originX += standardStepX;
		
				repaint();
		
				break;
		
		
				case RIGHT:
		
				originX -= standardStepX;
		
				repaint();
		
				break;
																							
				}
				
				if (downloadImageCanvasFlag == false) {	
				
					// for Canvas used in showing images in Album
					// enable this Canvas to use functions for navigating forward and backward through Album
					
				
					switch (keyCode) {
				
					case KEY_NUM1:
				
					imageAlbumReference.changePreviousPhoto(this);
				
					break;
				
					case KEY_NUM3:
				
					imageAlbumReference.changeNextPhoto(this);
				
					break;
				
					}
				
				}
			
			}
			
			else {	// keyPressed action for touch screen phone
					// navigation key UP or LEFT pressed -> navigate to previous image 
		 			// navigation key DOWN or RIGHT pressed -> navigate to next image 		
				
			
				if ((getGameAction(keyCode) == UP || getGameAction(keyCode) == LEFT) && downloadImageCanvasFlag == false){
			
					imageAlbumReference.changePreviousPhoto(this); 
		
				}
			
				if ((getGameAction(keyCode) == DOWN || getGameAction(keyCode) == RIGHT) && downloadImageCanvasFlag == false){ 
		
					imageAlbumReference.changeNextPhoto(this);
			
				}
			
			}
					
		}
		
		
		/**
		 *  Method for responding to pointerPressed action on phone -  record the coordinates of starting point
		 */
		
		protected void pointerPressed(int x, int y) {
		
			if (y < 239 ) {		// only respond to pointerPressed event occur outside command area (y coordinate < 239)
		
				pointerStartX = x;
		
				pointerStartY = y;
				
			}
		
		}
		
		
		/**
		 *  Method for responding to pointerDragged action on phone - calculate the distance that the pointer is dragged,
		 *	same distance and direction is used for moving the image  
		 */
		
		protected void pointerDragged(int x, int y) {
				
			
			if (y < 239 ) {		// only respond to pointerDragged event occur outside command area (y coordinate < 239)
				
				// drag to a direction to move the image in that direction	
								
				stepX = x - pointerStartX ;
		
				originX += stepX;
		
				stepY = y - pointerStartY ;		
		
				originY += stepY;
		
				pointerStartX = x;
		
				pointerStartY = y;
		
				repaint();
			
			}
		
		}
		
	}