TextView实现打印机效果 ,字符串逐字显示

https://github.com/lygttpod/AndroidCustomView/blob/master/app/src/main/java/com/allen/androidcustomview/widget/FadeInTextView.java

上述是自定义好的Textview，可以直接使用，具体如何实现，我们一起学习一下

 public class FadeInTextView extends TextView {

     private Rect textRect = new Rect();

     private StringBuffer stringBuffer = new StringBuffer();

     private String[] arr;

     private int textCount;

     private int currentIndex = -1;

     /**
      * 每个字出现的时间
      */
     private int duration = 300;
     private ValueAnimator textAnimation;

     private TextAnimationListener textAnimationListener;

     public FadeInTextView setTextAnimationListener(TextAnimationListener textAnimationListener) {
         this.textAnimationListener = textAnimationListener;
         return this;
     }

     public FadeInTextView(Context context) {
         this(context, null);
     }

     public FadeInTextView(Context context, @Nullable AttributeSet attrs) {
         super(context, attrs);

     }

     @Override
     protected void onDraw(final Canvas canvas) {
         super.onDraw(canvas);
         if (stringBuffer != null) {
             drawText(canvas, stringBuffer.toString());
         }
     }

     /**
      * 绘制文字
      *
      * @param canvas 画布
      */
     private void drawText(Canvas canvas, String textString) {
         textRect.left = getPaddingLeft();
         textRect.top = getPaddingTop();
         textRect.right = getWidth() - getPaddingRight();
         textRect.bottom = getHeight() - getPaddingBottom();
         Paint.FontMetricsInt fontMetrics = getPaint().getFontMetricsInt();
         int baseline = (textRect.bottom + textRect.top - fontMetrics.bottom - fontMetrics.top) / 2;
         //文字绘制到整个布局的中心位置
         canvas.drawText(textString, getPaddingLeft(), baseline, getPaint());
     }

     /**
      * 文字逐个显示动画  通过插值的方式改变数据源
      */
     private void initAnimation() {

         //从0到textCount - 1  是设置从第一个字到最后一个字的变化因子
         textAnimation = ValueAnimator.ofInt(0, textCount - 1);
         //执行总时间就是每个字的时间乘以字数
         textAnimation.setDuration(textCount * duration);
         //匀速显示文字
         textAnimation.setInterpolator(new LinearInterpolator());
         textAnimation.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
             @Override
             public void onAnimationUpdate(ValueAnimator valueAnimator) {
                 int index = (int) valueAnimator.getAnimatedValue();
                 //过滤去重，保证每个字只重绘一次
                 if (currentIndex != index) {
                     stringBuffer.append(arr[index]);
                     currentIndex = index;
                     //所有文字都显示完成之后进度回调结束动画
                     if (currentIndex == (textCount - 1)) {
                         if (textAnimationListener != null) {
                             textAnimationListener.animationFinish();
                         }
                     }

                     invalidate();
                 }
             }
         });
     }

     /**
      * 设置逐渐显示的字符串
      *
      * @param textString
      * @return
      */
     public FadeInTextView setTextString(String textString) {
         if (textString != null) {
             //总字数
             textCount = textString.length();
             //存放单个字的数组
             arr = new String[textCount];
             for (int i = 0; i < textCount; i++) {
                 arr[i] = textString.substring(i, i + 1);
             }
             initAnimation();
         }

         return this;
     }

     /**
      * 开启动画
      *
      * @return
      */
     public FadeInTextView startFadeInAnimation() {
         if (textAnimation != null) {
             stringBuffer.setLength(0);
             currentIndex = -1;
             textAnimation.start();
         }
         return this;
     }

     /**
      * 停止动画
      *
      * @return
      */
     public FadeInTextView stopFadeInAnimation() {
         if (textAnimation != null) {
             textAnimation.end();
         }
         return this;
     }

     /**
      * 回调接口
      */
     public interface TextAnimationListener {
         void animationFinish();
     }
 }

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在此说明，俺们也是看大神写的代码学习学习，并非自己写的，在此是供大家学习!