Blackberry上实现文字滚动效果

 博主doll还写了几篇BlackBerry开发的小文档，相当实用，感谢！

 

原文：

http://doll.javaeye.com/blog/569457

 

LabelField testLabel = new LabelField(  
            "I swear to god up in the sky I will be your shelter when you cry Cause you are my everything.",  
            Field.FOCUSABLE) {  
        int currentChar = 0;  
        String currentText = null;  
        Font ourFont;  
        private Timer _scrollTimer;  
        private TimerTask _scrollTimerTask;  
 
        protected void paint(Graphics graphics) {  
            currentText = this.getText();  
            if (currentChar < currentText.length()) {  
                currentText = currentText.substring(currentChar);  
            }  
            graphics.drawText(currentText, 0, 0, DrawStyle.ELLIPSIS, Display  
                    .getWidth());  
        }  
 
        protected void layout(int width, int height)  {  
            ourFont = this.getFont();  
            setExtent(Display.getWidth(), ourFont.getHeight());  
        }  
 
        protected void onDisplay() {  
            startScroll();  
        }  
 
        protected void onUnfocus() {  
            startScroll();  
        }  
 
        private void startScroll() {  
            // Start scrolling  
            final String fullText = this.getText();  
            if (_scrollTimer == null) {  
                _scrollTimer = new Timer();  
                _scrollTimerTask = new TimerTask() {  
                    public void run() {  
                        currentChar = currentChar + 4;  
                        if (currentChar > fullText.length()) {  
                            currentChar = 0;  
                        }  
                        invalidate();  
                    }  
                };  
                _scrollTimer.scheduleAtFixedRate(_scrollTimerTask, 500, 500);  
            }  
        }  
 
        protected void onFocus(int direction) {  
            if (_scrollTimer != null) {  
                _scrollTimerTask.cancel();  
                _scrollTimer.cancel();  
                _scrollTimer = null;  
                _scrollTimerTask = null;  
            }  
        }  
 
        protected boolean navigationMovement(int dx, int dy, int status,  
                int time) {  
            currentText = this.getText();  
            int oldCurrentChar = currentChar;  
            if (Math.abs(dx) > Math.abs(dy)) {  
                // horizontal scroll  
                if (dx > 0) {  
                    currentChar = Math.min(currentText.length() - 1,  
                            currentChar + 1);  
                } else if (dx < 0) {  
                    currentChar = Math.max(0, currentChar - 1);  
                }  
                if (oldCurrentChar != currentChar) {  
                    this.invalidate();  
                }  
                return true;  
            } else {  
                return super.navigationMovement(dx, dy, status, time);  
            }  
        }  
    };