BlackBerry-创建图像查看器

发布的代码将引发，IllegalStateException因为它试图直接从后台（计时器）线程修改UI元素：

animationField.setBitmap(image000);

您需要使用UiApplication.getUiApplication().invokeLater()或类似方法从后台线程修改UI。

另外，您可以让计时器连续调整位图字段的Alpha值（不透明度）以产生淡入淡出效果。

这是一个示例，从您提供的代码开始：

public class SlideTransition extends MainScreen {

   private final Bitmap image000 = Bitmap.getBitmapResource("img1.jpg");
   private final Bitmap image001 = Bitmap.getBitmapResource("img2.jpg");
   private final Bitmap image002 = Bitmap.getBitmapResource("img3.jpg");
   private AlphaBitmapField animationField = new AlphaBitmapField(image000);
   private Timer animationTimer = new Timer();
   private TimerTask animationTask;
   private final int animationPeriodMsec = 40; // 25 Hz animation timer

   public SlideTransition() {
      animationTask = new AnimationTask();

      add(animationField);
      animationTimer.scheduleAtFixedRate(animationTask, 0, animationPeriodMsec);  
   }

   // I separated your anonymous timer task into its own class for readability
   private class AnimationTask extends TimerTask {

      private final int fadeDurationMsec = 500;
      private final int displayDurationMsec = 1500;
      private final int fadeInEndCount = fadeDurationMsec / animationPeriodMsec;
      private final int fadeOutStartCount = (fadeDurationMsec + displayDurationMsec) / animationPeriodMsec;
      private final int endCount = (2 * fadeDurationMsec + displayDurationMsec) / animationPeriodMsec;

      private int imgCounter = 0;
      private int cycleCounter = 0;

      public void run() {
         if (cycleCounter >= endCount) {
            cycleCounter = 0;
         }
         Bitmap newImage = null;
         if (cycleCounter == 0) {
            // time to switch the images
            if (imgCounter == 0) {
               newImage = image000;
            } else if (imgCounter == 1) {
               newImage = image001;
            } else if (imgCounter == 2) {
               newImage = image002;
               imgCounter = -1;
            }
            imgCounter++;
         }

         // assign final variables to use inside a UI thread Runnable
         final Bitmap currentImage = newImage;
         final int i = cycleCounter;

         UiApplication.getUiApplication().invokeLater(new Runnable() {
            public void run() {
               if (i == 0) {
                  // switch images, and start with the image invisible (alpha = 0)
                  animationField.setAlpha(0);
                  animationField.setBitmap(currentImage);
               } else if (i <= fadeInEndCount) {
                  // fade in by changing alpha
                  animationField.setAlpha(i * 255 / fadeInEndCount);
               } else if (i >= fadeOutStartCount) {
                  // fade out by changing alpha
                  animationField.setAlpha(255 + (fadeOutStartCount - i) * 255 / (endCount - fadeOutStartCount));
               }               
            }
         });

         cycleCounter++;
      }
   }

   // this class extends BitmapField to allow alpha adjustment, and automatic repainting
   private class AlphaBitmapField extends BitmapField {

      private int _alpha;

      public AlphaBitmapField(Bitmap img) {
         super(img);
      }

      public void setAlpha(int alpha) {
         if (alpha != _alpha) {
            _alpha = alpha;
            // force a repaint
            invalidate();
         }
      }

      protected void paint(Graphics graphics) {
         graphics.setGlobalAlpha(_alpha);         
         super.paint(graphics);
      }
   }
}

我从您的代码中更改了时间值，但是您可以将它们修改为任意的值。我使动画计时器以每秒25个周期运行。我发现这对于智能手机动画来说是一个合理的价值。它的速度足以使它看起来相当平滑，但仅是人眼可以处理此类信息的速度的两倍……任何更快的速度都可能是浪费的。

我定义了一些常数，您可以使用这些常数来控制淡入和淡出所花费的时间（fadeDurationMsec）以及淡入和淡出之间所显示的每个图像的时间（displayDurationMsec）。所有值均以毫秒为单位。

有用的参考

BlackBerry AnimatedGIFField示例代码。

黑莓论坛关于淡入/淡出的话题