public void paint(Graphics g){ //清除屏幕 int color = g.getColor(); g.setColor(0xFFFFFF); g.fillRect(0,0,getWidth(),getHeight()); g.setColor(color); //計算整個菜單的高度，寬度和（x,y） int rectWidth = PReferWidth; int rectHeight = preferHeight * LABELS.length; int x = (getWidth()-rectWidth)/2; int y = (getHeight()-rectHeight)/2; //畫矩形 g.drawRect(x,y,rectWidth,rectHeight); for(int i = 1;i<LABELS.length;i++){ g.drawLine(x,y+preferHeight*i,x+rectWidth,y+preferHeight*i); } //畫菜單選項，并根據selected的值判定焦點 for(int j = 0;j<LABELS.length;j++){ if(selected == j){ g.setColor(0x6699cc); g.fillRect(x+1,y+j*preferHeight+1,rectWidth-1,preferHeight-1); g.setColor(color); } g.drawString(LABELS[j],x+8,y+j*preferHeight+4,Graphics.LEFTGraphics.TOP); } } 第二個重要的問題是：焦點的切換，在高級UI類中，這是不需要我們處理的。但是使用Canvas制作菜單需要自己來處理焦點的移動，這里我們定義一個int類型變量selected，來記錄焦點所在的菜單條目位置,也就是選擇的索引。當用戶按鍵的時候，我們在keyPressed()方法中判定用戶的移動方向，對selected進行相關的加減運算，然后repaint()整個屏幕即可。
public void keyPressed(int keyCode){ //根據用戶輸入更新selected的值，并重新繪制屏幕 int action = this.getGameAction(keyCode); switch(action){ case Canvas.FIRE: printLabel(selected); break; case Canvas.DOWN: selected = (selected+1)%4; break; case Canvas.UP:{ if(--selected < 0){ selected+=4; } break; } default: break; } repaint(); serviceRepaints(); } 這樣我們就制作出了一個基本的菜單，你還可以發揮想象給被選中的菜單增加動畫效果。MenUCanvas的代碼如下所示：
package com.j2medev.chapter3;
import javax.microedition.lcdui.*;
public class MenuCanvas extends Canvas{
//selected變量標記了焦點位置 private int selected = 0; private int preferWidth = -1; private int preferHeight = -1; public static final int[] OPTIONS = {0,1,2,3}; public static final String[] LABELS={"New Game","Setttings","High Scores","Exit"};
public MenuCanvas() { selected = OPTIONS[0]; //計算菜單選項的長度和高度值 Font f = Font.getDefaultFont(); for(int i = 0;i<LABELS.length;i++){ int temp = f.stringWidth(LABELS[i]); if(temp > preferWidth){ preferWidth = temp; } } preferWidth = preferWidth + 2*8; preferHeight = f.getHeight()+2*4; }
public void paint(Graphics g){ //清除屏幕 int color = g.getColor(); g.setColor(0xFFFFFF); g.fillRect(0,0,getWidth(),getHeight()); g.setColor(color); //計算整個菜單的高度，寬度和（x,y） int rectWidth = preferWidth; int rectHeight = preferHeight * LABELS.length; int x = (getWidth()-rectWidth)/2; int y = (getHeight()-rectHeight)/2; //畫矩形 g.drawRect(x,y,rectWidth,rectHeight); for(int i = 1;i<LABELS.length;i++){ g.drawLine(x,y+preferHeight*i,x+rectWidth,y+preferHeight*i); } //畫菜單選項，并根據selected的值判定焦點 for(int j = 0;j<LABELS.length;j++){ if(selected == j){ g.setColor(0x6699cc); g.fillRect(x+1,y+j*preferHeight+1,rectWidth-1,preferHeight-1); g.setColor(color); } g.drawString(LABELS[j],x+8,y+j*preferHeight+4,Graphics.LEFTGraphics.TOP); } }
public void keyPressed(int keyCode){ //根據用戶輸入更新selected的值，并重新繪制屏幕 int action = this.getGameAction(keyCode); switch(action){ case Canvas.FIRE: printLabel(selected); break; case Canvas.DOWN: selected = (selected+1)%4; break; case Canvas.UP:{ if(--selected < 0){ selected+=4; } break; } default: break; } repaint(); serviceRepaints(); } //showNotify()在paint()之前被調用 public void showNotify(){ System.out.println("showNotify() is called"); } private void printLabel(int selected){ System.out.println(LABELS[selected]); } }
