实例解析如何在Android应用中实现弹幕动画效果

public class BarrageItem { 
  public TextView textView; 
  public int textColor; 
  public String text; 
  public int textSize; 
  public int moveSpeed;//移动速度 
  public int verticalPos;//垂直方向显示的位置 
  public int textMeasuredWidth;//字体显示占据的宽度 
} 

  private Context mContext; 
  private BarrageHandler mHandler = new BarrageHandler(); 
  private Random random = new Random(System.currentTimeMillis()); 
  private static final long BARRAGE_GAP_MIN_DURATION = 1000;//两个弹幕的最小间隔时间 
  private static final long BARRAGE_GAP_MAX_DURATION = 2000;//两个弹幕的最大间隔时间 
  private int maxSpeed = 10000;//速度，ms 
  private int minSpeed = 5000;//速度，ms 
  private int maxSize = 30;//文字大小，dp 
  private int minSize = 15;//文字大小，dp 
 
  private int totalHeight = 0; 
  private int lineHeight = 0;//每一行弹幕的高度 
  private int totalLine = 0;//弹幕的行数 
  private String[] itemText = {"是否需要帮忙", "what are you 弄啥来", "哈哈哈哈哈哈哈", "抢占沙发。。。。。。", "************", "是否需要帮忙","我不会轻易的狗带", "嘿嘿", "这是我见过的最长长长长长长长长长长长的评论"}; 
  private int textCount; 
//  private List<BarrageItem> itemList = new ArrayList<BarrageItem>(); 
 
  public BarrageView(Context context) { 
    this(context, null); 
  } 
 
  public BarrageView(Context context, AttributeSet attrs) { 
    this(context, attrs, 0); 
  } 
 
  public BarrageView(Context context, AttributeSet attrs, int defStyleAttr) { 
    super(context, attrs, defStyleAttr); 
    mContext = context; 
    init(); 
  } 

@Override 
public void onWindowFocusChanged(boolean hasWindowFocus) { 
  super.onWindowFocusChanged(hasWindowFocus); 
  totalHeight = getMeasuredHeight(); 
  lineHeight = getLineHeight(); 
  totalLine = totalHeight / lineHeight; 
} 
    通过Handler的sendEmptyMessageDelayed每隔随机的时间产生一个弹幕项。下面的代码设置弹幕项的属性。
 
class BarrageHandler extends Handler { 
  @Override 
  public void handleMessage(Message msg) { 
    super.handleMessage(msg); 
    generateItem(); 
    //每个弹幕产生的间隔时间随机 
    int duration = (int) ((BARRAGE_GAP_MAX_DURATION - BARRAGE_GAP_MIN_DURATION) * Math.random()); 
    this.sendEmptyMessageDelayed(0, duration); 
  } 
} 
 
private void generateItem() { 
  BarrageItem item = new BarrageItem(); 
  String tx = itemText[(int) (Math.random() * textCount)]; 
  int sz = (int) (minSize + (maxSize - minSize) * Math.random()); 
  item.textView = new TextView(mContext); 
  item.textView.setText(tx); 
  item.textView.setTextSize(sz); 
  item.textView.setTextColor(Color.rgb(random.nextInt(256), random.nextInt(256), random.nextInt(256))); 
  item.textMeasuredWidth = (int) getTextWidth(item, tx, sz); 
  item.moveSpeed = (int) (minSpeed + (maxSpeed - minSpeed) * Math.random()); 
  if (totalLine == 0) { 
    totalHeight = getMeasuredHeight(); 
    lineHeight = getLineHeight(); 
    totalLine = totalHeight / lineHeight; 
  } 
  item.verticalPos = random.nextInt(totalLine) * lineHeight; 
  showBarrageItem(item); 
} 

private void showBarrageItem(final BarrageItem item) { 
 
    int leftMargin = this.getRight() - this.getLeft() - this.getPaddingLeft(); 
 
    LayoutParams params = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); 
    params.addRule(RelativeLayout.ALIGN_PARENT_TOP); 
    params.topMargin = item.verticalPos; 
    this.addView(item.textView, params); 
    Animation anim = generateTranslateAnim(item, leftMargin); 
    anim.setAnimationListener(new Animation.AnimationListener() { 
      @Override 
      public void onAnimationStart(Animation animation) { 
 
      } 
 
      @Override 
      public void onAnimationEnd(Animation animation) { 
        item.textView.clearAnimation(); 
        BarrageView.this.removeView(item.textView); 
      } 
 
      @Override 
      public void onAnimationRepeat(Animation animation) { 
 
      } 
    }); 
    item.textView.startAnimation(anim); 
  } 
 
  private TranslateAnimation generateTranslateAnim(BarrageItem item, int leftMargin) { 
    TranslateAnimation anim = new TranslateAnimation(leftMargin, -item.textMeasuredWidth, 0, 0); 
    anim.setDuration(item.moveSpeed); 
    anim.setInterpolator(new AccelerateDecelerateInterpolator()); 
    anim.setFillAfter(true); 
    return anim; 
  }