Android自定义View实现竖直跑马灯效果案例解析

首先给出跑马灯效果图

 

中间的色块是因为视频转成GIF造成的失真，自动忽略哈。
大家知道，横向的跑马灯Android自带的TextView就可以实现，详情请百度【Android跑马灯效果】。但是竖直的跑马灯效果原生Android是不支持的。网上也有很多网友实现了自定义的效果，但是我一贯是不喜欢看别人的代码，所以这篇博客的思路完全是我自己的想法哈。 

首先，我们需要给自定义的控件梳理一下格局，如下图所示： 

1、首先我们将控件分为三个区块，上面绿色部分为消失不可见的块，中间黑色部分为可见区域，下面红色部分为欲出现不可见区域。蓝色的线代表的是整个控件的上线和下线。 
2、首先我们只给出两个文字块在内存中，分别是黑色部分的可见块和红色部分的欲出现块。 
3、求出这些块的宽度、高度与中心点的坐标值。 
4、滚动时，动态地改变每个块的中心点y坐标，使之向上平移。 
5、当平移结束后，可见块位于欲消失的不可见块，欲出现的可见块位于可见区域的文字块。此时将欲消失的文字块移除List，并重新设置后一个索引的Text和重心坐标值，重新加入List中，刷新。 
6、用一个Handler来处理动画的间隔时间。用属性动画ValueAnimator来实现平移的动画效果。 

下面开始代码讲解，首先是用链式设置法设置一些常规属性： 

<span style="font-size:14px;"> public VerticalMarqueeView color(int color){
  this.color = color;
  return this;
 }
 public VerticalMarqueeView textSize(int textSize){
  this.textSize = textSize;
  return this;
 }
 public VerticalMarqueeView datas(String[] datas){
  this.datas = datas;
  return this;
 }
 public void commit(){
  if(this.datas == null || datas.length == 0){
   Log.e("VerticalMarqueeView", "the datas's length is illegal");
   throw new IllegalStateException("may be not invoke the method named datas(String[])");
  }
  paint.setColor(color);
  paint.setTextSize(textSize);
 }</span>

最后一定要调用commit方法进行提交，通过代码可以看出来这里除了有排空措施，还有最重要的一步：设置字体的大小。
然后我抽象出一个文字块的bean类： 

 public class TextBlock {
  private int width;
  private int height;
  private String text;
  private int drawX;
  private int drawY;
  private Paint paint;
  private int position;
  public TextBlock(int width, int height, Paint paint){
   this.width = width;
   this.height = height;
   this.paint = paint;
  }
  public void reset(int centerY){
   reset(text, centerX, centerY, position);
  }
  public void reset(String text, int centerY){
   reset(text, centerX, centerY, position);
  }
  public void reset(String text, int centerY, int position){
   reset(text, centerX, centerY, position);
  }
  public void reset(String text, int centerX, int centerY, int position){
   this.text = text;
   this.position = position;
   int measureWidth = (int)paint.measureText(text);
   drawX = (width - measureWidth) / 2;
   FontMetrics metrics = paint.getFontMetrics();
   drawY = (int)(centerY + (metrics.bottom - metrics.top) / 2 - metrics.bottom);
  }
  public int getPosition(){
   return position;
  }
  public void draw(canvas canvas){
   canvas.drawText(text, drawX, drawY, paint);
  }
 }

这个bean类，最重要的方法就是几个重载的reset方法，通过改变centerY的值，来动态得改变绘制文字的起点实现居中绘制。关于文字的居中绘制请参考百度【android canvas 居中绘制文本】。
然后是重写onMeasure方法 

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec){
  super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  if(this.datas == null || this.datas.length == 0){
   Log.e("VerticalMarqueeView", "the datas's length is illegal");
   return;
  }
  width = MeasureSpec.getSize(widthMeasureSpec) - getPaddingLeft() - getPaddingRight();
  height = MeasureSpec.getSize(heightMeasureSpec) - getPaddingTop() - getPaddingBottom();
  centerX = width / 2;
  centerY = height / 2;
  blocks.clear();
  //添加显示区域的文字块
  TextBlock block1 = new TextBlock(width, height, paint);
  block1.reset(datas[0], centerX, centerY, 0);
  blocks.add(block1);
  if(datas.length > 1){   
   TextBlock block2 = new TextBlock(width, height, paint);
   block2.reset(datas[1], centerX, centerY + height, 1);
   blocks.add(block2);
  }
 }

在这个方法中，首先进行非空判断以免出现致命逻辑错误。然后得到整个控件的宽高和重心坐标。然后实例化两个文字块TextBlock，第一个文字块通过reset设置中点y坐标为整个控件的中点y坐标，第二个文字块通过reset设置中点y坐标为centerY+height，意思就是置于下一个文字块的不可见区域内。
 然后是onDraw方法，这个方法非常简单，已经将业务逻辑转交给TextBlock的draw方法了。 

 @Override
 protected void onDraw(Canvas canvas){
  for(int i = 0; i < blocks.size(); i++){
   blocks.get(i).draw(canvas);
  }
 }

最关键的就是滚动效果的实现了，首先我们给出两个方法，开始滚动和结束滚动。 

 public void startScroll(){
  isStopScroll = false;
  if(datas == null || datas.length == 0 || datas.length == 1){
   Log.e("VerticalMarqueeView", "the datas's length is illegal");
   return;
  }
  if(!isStopScroll){
   handler.postDelayed(new Runnable(){
    @Override
    public void run(){
     scroll();
     if(!isStopScroll){
      handler.postDelayed(this, DURATION_SCROLL);
     }
    }
   }, DURATION_SCROLL);
  }
 }
 public void stopScroll(){
  this.isStopScroll = true;
 }

原理很简单，首先给出一个boolean标志isStopScroll。然后用Handler的postDelayed方法进行循环延迟得调用scroll方法进行滚动。接下来给出全文最重要的方法，scroll方法。 

private void scroll(){
  ValueAnimator animator = ValueAnimator.ofPropertyValuesHolder(PropertyValuesHolder.ofInt("scrollY", centerY, centerY - height));
  animator.setDuration(DURATION_ANIMATOR);
  animator.addUpdateListener(new AnimatorUpdateListener(){
   @Override
   public void onAnimationUpdate(ValueAnimator animation){
    int scrollY = (int)animation.getAnimatedValue("scrollY");
    blocks.get(0).reset(scrollY);
    blocks.get(1).reset(scrollY + height);
    invalidate();
   }
  });
  animator.addListener(new AnimatorListener(){
   @Override
   public void onAnimationStart(Animator animation){
   }
   @Override
   public void onAnimationRepeat(Animator animation){
   }
   @Override
   public void onAnimationEnd(Animator animation){
    //移除第一块
    int position = blocks.get(1).getPosition();
    TextBlock textBlock = blocks.remove(0);
    //最后一个
    if(position == datas.length - 1){
     position = 0;
    }else{
     position ++;
    }
    textBlock.reset(datas[position], centerY + height, position);
    blocks.add(textBlock);
    invalidate();
   }
   @Override
   public void onAnimationCancel(Animator animation){
   }
  });
  animator.start();
 }

首先采用ValueAnimator类进行属性动画，开始值为控件的中点y坐标，结束值为centerY-height，意味着要从下往上移动一个文字块的距离。然后在动画更新回调方法中，进行对文字块的reset方法。当动画结束后，得到第二个文字块的position值，然后移除第一个文字块，重新reset这个文字块的索引值，再加入到List的容器中。如此循坏。
最后给一个get方法返回position吧。 

 public int getCurrentPosition(){
  if(datas == null || datas.length == 0){
   return -1;
  }
  if(datas.length == 1 && blocks.size() == 1){
   return 0;
  }
  return blocks.get(0).getPosition();
 }

上述就将这个自定义控件的所有代码都呈现出来了，考虑到比较零散，这里讲所有代码都打印出来： 

package cc.wxf.component;
import android.animation.Animator;
import android.animation.Animator.AnimatorListener;
import android.animation.PropertyValuesHolder;
import android.animation.ValueAnimator;
import android.animation.ValueAnimator.AnimatorUpdateListener;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.FontMetrics;
import android.os.Handler;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import java.util.ArrayList;
import java.util.List;
public class VerticalMarqueeView extends View{
 public static final int DURATION_SCROLL = 3000;
 public static final int DURATION_ANIMATOR = 1000;
 private int color = Color.BLACK;
 private int textSize = 30;
 private String[] datas = null;
 private int width;
 private int height;
 private int centerX;
 private int centerY;
 private List<TextBlock> blocks = new ArrayList<TextBlock>(2);
 private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
 private Handler handler = new Handler();
 private boolean isStopScroll = false;
 public VerticalMarqueeView(Context context, AttributeSet attrs, int defStyleAttr){
  super(context, attrs, defStyleAttr);
 }
 public VerticalMarqueeView(Context context, AttributeSet attrs){
  super(context, attrs);
 }
 public VerticalMarqueeView(Context context){
  super(context);
 }
 public VerticalMarqueeView color(int color){
  this.color = color;
  return this;
 }
 public VerticalMarqueeView textSize(int textSize){
  this.textSize = textSize;
  return this;
 }
 public VerticalMarqueeView datas(String[] datas){
  this.datas = datas;
  return this;
 }
 public void commit(){
  if(this.datas == null || datas.length == 0){
   Log.e("VerticalMarqueeView", "the datas's length is illegal");
   throw new IllegalStateException("may be not invoke the method named datas(String[])");
  }
  paint.setColor(color);
  paint.setTextSize(textSize);
 }
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec){
  super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  if(this.datas == null || this.datas.length == 0){
   Log.e("VerticalMarqueeView", "the datas's length is illegal");
   return;
  }
  width = MeasureSpec.getSize(widthMeasureSpec) - getPaddingLeft() - getPaddingRight();
  height = MeasureSpec.getSize(heightMeasureSpec) - getPaddingTop() - getPaddingBottom();
  centerX = width / 2;
  centerY = height / 2;
  blocks.clear();
  //添加显示区域的文字块
  TextBlock block1 = new TextBlock(width, height, paint);
  block1.reset(datas[0], centerX, centerY, 0);
  blocks.add(block1);
  if(datas.length > 1){   
   TextBlock block2 = new TextBlock(width, height, paint);
   block2.reset(datas[1], centerX, centerY + height, 1);
   blocks.add(block2);
  }
 }
 @Override
 protected void onDraw(Canvas canvas){
  for(int i = 0; i < blocks.size(); i++){
   blocks.get(i).draw(canvas);
  }
 }
 public void startScroll(){
  isStopScroll = false;
  if(datas == null || datas.length == 0 || datas.length == 1){
   Log.e("VerticalMarqueeView", "the datas's length is illegal");
   return;
  }
  if(!isStopScroll){
   handler.postDelayed(new Runnable(){
    @Override
    public void run(){
     scroll();
     if(!isStopScroll){
      handler.postDelayed(this, DURATION_SCROLL);
     }
    }
   }, DURATION_SCROLL);
  }
 }
 public void stopScroll(){
  this.isStopScroll = true;
 }
 private void scroll(){
  ValueAnimator animator = ValueAnimator.ofPropertyValuesHolder(PropertyValuesHolder.ofInt("scrollY", centerY, centerY - height));
  animator.setDuration(DURATION_ANIMATOR);
  animator.addUpdateListener(new AnimatorUpdateListener(){
   @Override
   public void onAnimationUpdate(ValueAnimator animation){
    int scrollY = (int)animation.getAnimatedValue("scrollY");
    blocks.get(0).reset(scrollY);
    blocks.get(1).reset(scrollY + height);
    invalidate();
   }
  });
  animator.addListener(new AnimatorListener(){
   @Override
   public void onAnimationStart(Animator animation){
   }
   @Override
   public void onAnimationRepeat(Animator animation){
   }
   @Override
   public void onAnimationEnd(Animator animation){
    //移除第一块
    int position = blocks.get(1).getPosition();
    TextBlock textBlock = blocks.remove(0);
    //最后一个
    if(position == datas.length - 1){
     position = 0;
    }else{
     position ++;
    }
    textBlock.reset(datas[position], centerY + height, position);
    blocks.add(textBlock);
    invalidate();
   }
   @Override
   public void onAnimationCancel(Animator animation){
   }
  });
  animator.start();
 }
 public int getCurrentPosition(){
  if(datas == null || datas.length == 0){
   return -1;
  }
  if(datas.length == 1 && blocks.size() == 1){
   return 0;
  }
  return blocks.get(0).getPosition();
 }
 public class TextBlock {
  private int width;
  private int height;
  private String text;
  private int drawX;
  private int drawY;
  private Paint paint;
  private int position;
  public TextBlock(int width, int height, Paint paint){
   this.width = width;
   this.height = height;
   this.paint = paint;
  }
  public void reset(int centerY){
   reset(text, centerX, centerY, position);
  }
  public void reset(String text, int centerY){
   reset(text, centerX, centerY, position);
  }
  public void reset(String text, int centerY, int position){
   reset(text, centerX, centerY, position);
  }
  public void reset(String text, int centerX, int centerY, int position){
   this.text = text;
   this.position = position;
   int measureWidth = (int)paint.measureText(text);
   drawX = (width - measureWidth) / 2;
   FontMetrics metrics = paint.getFontMetrics();
   drawY = (int)(centerY + (metrics.bottom - metrics.top) / 2 - metrics.bottom);
  }
  public int getPosition(){
   return position;
  }
  public void draw(Canvas canvas){
   canvas.drawText(text, drawX, drawY, paint);
  }
 }
}

最后给出使用的方法，很简单。

package cc.wxf.androiddemo;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import cc.wxf.component.VerticalMarqueeView;
public class MainActivity extends Activity {
 private VerticalMarqueeView vmView;
 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  vmView = (VerticalMarqueeView)findViewById(R.id.vmView);
  String[] datas = new String[]{
    "南海又开始动荡了","菲律宾到处都在肇事","这次为了一张审判废纸，菲律宾投入了多少成本呢","测试数据4","测试数据5为了长度不一样","就把这条当做测试数据吧"
  };
  vmView.color(getResources().getColor(android.R.color.black))
    .textSize(sp2px(this, 15))
    .datas(datas).commit();
  vmView.startScroll();
  vmView.setOnClickListener(new View.OnClickListener(){
   @Override
   public void onClick(View v){
    Toast.makeText(MainActivity.this, "当前的索引为：" + vmView.getCurrentPosition(), Toast.LENGTH_SHORT).show();
   }
  });
 }
 private int sp2px(Context context, int sp){
  float density = context.getResources().getDisplayMetrics().scaledDensity;
  return (int) (sp * density + 0.5f);
 }
 @Override
 protected void onDestroy() {
  super.onDestroy();
  //必须要调用，否则内存中会一直无限循环
  vmView.stopScroll();
 }
}

demo就不提供了，自定义View就只有上面一个文件。

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