属性动画高级运用

1、自定义TypeEvaluator

1、TypeEvaluator的作用

  • 告诉动画系统如何从初始值过度到结束值

2、FloatEvaluator的代码实现:

  • evaluate()方法当中传入了三个参数,第一个参数fraction非常重要,这个参数用于表示动画的完成度的,我们应该根据它来计算当前动画的值应该是多少,第二第三个参数分别表示动画的初始值和结束值。那么上述代码的逻辑就比较清晰了,用结束值减去初始值,算出它们之间的差值,然后乘以fraction这个系数,再加上初始值,那么就得到当前动画的值了。

    public class FloatEvaluator implements TypeEvaluator {  
      public Object evaluate(float fraction, Object startValue, Object endValue) {  
          float startFloat = ((Number) startValue).floatValue();  
          return startFloat + fraction * (((Number) endValue).floatValue() - startFloat);  
      }  
    }  
    

3、使用ValueAnimator.ofObject()时,自定义TypeEvaluator

  • 先定义一个Point类

    public class Point {  
    
      private float x;  
    
      private float y;  
    
      public Point(float x, float y) {  
          this.x = x;  
          this.y = y;  
      }  
    
      public float getX() {  
          return x;  
      }  
    
      public float getY() {  
          return y;  
      }  
    
    }  
    
  • 定义PointEvaluator

    public class PointEvaluator implements TypeEvaluator{  
    
      @Override  
      public Object evaluate(float fraction, Object startValue, Object endValue) {  
          Point startPoint = (Point) startValue;  
          Point endPoint = (Point) endValue;  
          float x = startPoint.getX() + fraction * (endPoint.getX() - startPoint.getX());  
          float y = startPoint.getY() + fraction * (endPoint.getY() - startPoint.getY());  
          Point point = new Point(x, y);  
          return point;  
      }  
    
    }  
    
  • 自定义ColorEvaluator(ObjectAnimator必须保证作用对象有set和get)

    public class ColorEvaluator implements TypeEvaluator {  
    
          private int mCurrentRed = -1;  
    
          private int mCurrentGreen = -1;  
    
          private int mCurrentBlue = -1;  
    
          @Override  
          public Object evaluate(float fraction, Object startValue, Object endValue) {  
              String startColor = (String) startValue;  
              String endColor = (String) endValue;  
              int startRed = Integer.parseInt(startColor.substring(1, 3), 16);  
              int startGreen = Integer.parseInt(startColor.substring(3, 5), 16);  
              int startBlue = Integer.parseInt(startColor.substring(5, 7), 16);  
              int endRed = Integer.parseInt(endColor.substring(1, 3), 16);  
              int endGreen = Integer.parseInt(endColor.substring(3, 5), 16);  
              int endBlue = Integer.parseInt(endColor.substring(5, 7), 16);  
              // 初始化颜色的值  
              if (mCurrentRed == -1) {  
                  mCurrentRed = startRed;  
              }  
              if (mCurrentGreen == -1) {  
                  mCurrentGreen = startGreen;  
              }  
              if (mCurrentBlue == -1) {  
                  mCurrentBlue = startBlue;  
              }  
              // 计算初始颜色和结束颜色之间的差值  
              int redDiff = Math.abs(startRed - endRed);  
              int greenDiff = Math.abs(startGreen - endGreen);  
              int blueDiff = Math.abs(startBlue - endBlue);  
              int colorDiff = redDiff + greenDiff + blueDiff;  
              if (mCurrentRed != endRed) {  
                  mCurrentRed = getCurrentColor(startRed, endRed, colorDiff, 0,  
                  fraction);  
              } else if (mCurrentGreen != endGreen) {  
                  mCurrentGreen = getCurrentColor(startGreen, endGreen, colorDiff,  
                  redDiff, fraction);  
              } else if (mCurrentBlue != endBlue) {  
                  mCurrentBlue = getCurrentColor(startBlue, endBlue, colorDiff,  
                  redDiff + greenDiff, fraction);  
              }  
              // 将计算出的当前颜色的值组装返回  
              String currentColor = "#" + getHexString(mCurrentRed)  
              + getHexString(mCurrentGreen) + getHexString(mCurrentBlue);  
              return currentColor;  
          }  
    
          /** 
           * 根据fraction值来计算当前的颜色。 
           */  
          private int getCurrentColor(int startColor, int endColor, int colorDiff,  
          int offset, float fraction) {  
              int currentColor;  
              if (startColor > endColor) {  
                  currentColor = (int) (startColor - (fraction * colorDiff - offset));  
                  if (currentColor < endColor) {  
                      currentColor = endColor;  
                  }  
              } else {  
                  currentColor = (int) (startColor + (fraction * colorDiff - offset));  
                  if (currentColor > endColor) {  
                      currentColor = endColor;  
                  }  
              }  
              return currentColor;  
          }  
    
          /** 
           * 将10进制颜色值转换成16进制。 
           */  
          private String getHexString(int value) {  
              String hexString = Integer.toHexString(value);  
              if (hexString.length() == 1) {  
                  hexString = "0" + hexString;  
              }  
              return hexString;  
          }  
    
      }  
    
  • 使用

    public class MyAnimView extends View {  
    
      public static final float RADIUS = 50f;  
    
      private Point currentPoint;  
    
      private Paint mPaint;  
    
      public MyAnimView(Context context, AttributeSet attrs) {  
          super(context, attrs);  
          mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);  
          mPaint.setColor(Color.BLUE);  
      }  
    
      private String color;  
    
      public String getColor() {  
          return color;  
      }  
    
      public void setColor(String color) {  
          this.color = color;  
          mPaint.setColor(Color.parseColor(color));  
          invalidate();  
      }  
    
      @Override  
      protected void onDraw(Canvas canvas) {  
          if (currentPoint == null) {  
              currentPoint = new Point(RADIUS, RADIUS);  
              drawCircle(canvas);  
              startAnimation();  
          } else {  
              drawCircle(canvas);  
          }  
      }  
    
      private void drawCircle(Canvas canvas) {  
          float x = currentPoint.getX();  
          float y = currentPoint.getY();  
          canvas.drawCircle(x, y, RADIUS, mPaint);  
      }  
    
      private void startAnimation() {  
          Point startPoint = new Point(RADIUS, RADIUS);  
          Point endPoint = new Point(getWidth() - RADIUS, getHeight() - RADIUS);  
          ValueAnimator anim = ValueAnimator.ofObject(new PointEvaluator(), startPoint, endPoint);  
          anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {  
              @Override  
              public void onAnimationUpdate(ValueAnimator animation) {  
                  currentPoint = (Point) animation.getAnimatedValue();  
                  invalidate();  
              }  
          });  
          ObjectAnimator anim2 = ObjectAnimator.ofObject(this, "color", new ColorEvaluator(),   
              "#0000FF", "#FF0000");  
          AnimatorSet animSet = new AnimatorSet();  
          animSet.play(anim).with(anim2);  
          animSet.setDuration(5000);  
          animSet.start();  
      }  
    
    }  
    
  • 效果


    20150504225554203.gif

2、自定义TimeInterpolator

1、TimeInterpolator

  • 它的主要作用是可以控制动画的变化速率,比如去实现一种非线性运动的动画效果。

2、 TimeInterpolator源码

  • 只有一个getInterpolation()方法。大家有兴趣可以通过注释来对这个接口进行详解的了解,这里我就简单解释一下,getInterpolation()方法中接收一个input参数,这个参数的值会随着动画的运行而不断变化,不过它的变化是非常有规律的,就是根据设定的动画时长匀速增加,变化范围是0到1。也就是说当动画一开始的时候input的值是0,到动画结束的时候input的值是1,而中间的值则是随着动画运行的时长在0到1之间变化的。

  • nput的值是由系统经过计算后传入到getInterpolation()方法中的,然后我们可以自己实现getInterpolation()方法中的算法,根据input的值来计算出一个返回值,而这个返回值就是fraction了。

    public interface TimeInterpolator {  
    
        float getInterpolation(float input);  
    }  
    

3、自定义DecelerateAccelerateInterpolator,实现先减速后加速的效果

  • DecelerateAccelerateInterpolato

    public class DecelerateAccelerateInterpolator implements TimeInterpolator{  
    
      @Override  
      public float getInterpolation(float input) {  
          float result;  
          if (input <= 0.5) {  
              result = (float) (Math.sin(Math.PI * input)) / 2;  
          } else {  
              result = (float) (2 - Math.sin(Math.PI * input)) / 2;  
          }  
          return result;  
      }  
    
    }  
    
  • 使用效果 anim.setInterpolator(new DecelerateAccelerateInterpolator());

    20150530230114481.gif

  • 另外,系统提供了BounceInterpolator,是一种可以模拟物理规律,实现反复弹起效果的Interpolator


    20150530230521897.gif

你可能感兴趣的:(属性动画高级运用)