Android自定义View实现弹幕效果

public class Textitem {
 private String content;
 private float fx;
 private float fy;
 private float perstep;
 private int textcolor;
 
 public Textitem(String content,float fx,float fy,float perstep,int textcolor){
  this.content = content;
  this.fx = fx;
  this.fy = fy;
  this.perstep = perstep;
  this.textcolor = textcolor;
 }
 
 public String getContent(){
  return content;
 }
 
 public void setContent(String content){
  this.content = content;
 }
 
 public int getTextcolor(){
  return textcolor;
 }
 
 public void setTextcolor(int textcolor){
  this.textcolor = textcolor;
 }
 
 public float getFx(){
   return fx;
 }
 
 public void setFx(float fx){
  this.fx = fx;
 }
 
 public float getFy(){
  return fy;
 }
 
 public void setFy(float fy){
  this.fy = fy;
 }
 
 public float getPerstep(){
  return perstep;
 }
 
 public void setPerstep(){
  fx -= perstep;
 }
}

public class barrageview extends View implements Runnable{
 
 private List<Textitem> items = new ArrayList<>();
 Random random = new Random();
 private Paint paint;
 
 public barrageview(Context context) {
  super(context);
  initpaint();
  new Thread(this).start();
 }
 
 public barrageview(Context context, AttributeSet attrs) {
  super(context, attrs);
  initpaint();
  new Thread(this).start();
 }
 
 public barrageview(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  initpaint();
  new Thread(this).start();
 }
 
 
 public void addTextitem(String content){
  float x = random.nextFloat()*getWidth();
  float y = Math.abs(random.nextFloat()*(getHeight()-50))+40;
  float step = random.nextFloat()*50;
  int r = random.nextInt(255);
  int g = random.nextInt(255);
  int b = random.nextInt(255);
  Textitem item = new Textitem(content,x,y,step, Color.rgb(r,g,b));
  items.add(item);
 }
 
 public void initpaint(){
  paint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
  paint.setColor(Color.RED);
  paint.setTextSize(30);
 }
 
 @Override
 public void draw(Canvas canvas) {
  super.draw(canvas);
  for(Textitem item:items){
   paint.setColor(item.getTextcolor());
   canvas.drawText(item.getContent(),item.getFx(),item.getFy(),paint);
  }
 }
 
 @Override
 public void run() {
  while(true){
   try{
    Thread.sleep(600);
    for(Textitem item:items){
     item.setPerstep();
    }
    postInvalidate();
   } catch (InterruptedException e){
    e.printStackTrace();
   }
  }
 }
}