主要介绍一下Scroller这个类，它可以实现过渡滑动的效果，使滑动看起来不是那么生硬，当然它用大量的重绘来实现，invalidate();通过源码看：

看构造方法

/**   * Create a Scroller with the default duration and interpolator.   */  public Scroller(Context context) {    this(context, null);  }  /**   * Create a Scroller with the specified interpolator. If the interpolator is   * null, the default (viscous) interpolator will be used. "Flywheel" behavior will   * be in effect for apps targeting Honeycomb or newer.   */  public Scroller(Context context, Interpolator interpolator) {    this(context, interpolator,        context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.HONEYCOMB);  }  /**   * Create a Scroller with the specified interpolator. If the interpolator is   * null, the default (viscous) interpolator will be used. Specify whether or   * not to support progressive "flywheel" behavior in flinging.   */  public Scroller(Context context, Interpolator interpolator, boolean flywheel) {    mFinished = true;    if (interpolator == null) {      mInterpolator = new ViscousFluidInterpolator();    } else {      mInterpolator = interpolator;    }    mPpi = context.getResources().getDisplayMetrics().density * 160.0f;    mDeceleration = computeDeceleration(ViewConfiguration.getScrollFriction());    mFlywheel = flywheel;    mPhysicalCoeff = computeDeceleration(0.84f); // look and feel tuning  }

我们用默认的就行，传个context就行了，其他的什么差值器，先不管了

然后调用startScroll，传递我们歧视滑动位置和滑动的偏移量，还有可选的默认持续时间，默认为250毫秒这个方法是用来赋值的，接下来会调用invalidate()进行重新绘制，然后就会onDraw()，这时候会调用computeScroll()这个方法，我们重写这个方法，computeScrollOffset()是判断动画有没有结束的一个方法，没结束的时候，我们根据滑动的偏移位置进行移动也就是scrollto到scroller的当前位置，再次调用invalidate()，由此无数的重回进行拼接形成了平滑的滑动

/**   * Call this when you want to know the new location. If it returns true,   * the animation is not yet finished.   */  public boolean computeScrollOffset() {    if (mFinished) {      return false;    }    int timePassed = (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime);    if (timePassed < mDuration) {      switch (mMode) {      case SCROLL_MODE:        final float x = mInterpolator.getInterpolation(timePassed * mDurationReciprocal);        mCurrX = mStartX + Math.round(x * mDeltaX);        mCurrY = mStartY + Math.round(x * mDeltaY);        break;      case FLING_MODE:        final float t = (float) timePassed / mDuration;        final int index = (int) (NB_SAMPLES * t);        float distanceCoef = 1.f;        float velocityCoef = 0.f;        if (index < NB_SAMPLES) {          final float t_inf = (float) index / NB_SAMPLES;          final float t_sup = (float) (index + 1) / NB_SAMPLES;          final float d_inf = SPLINE_POSITION[index];          final float d_sup = SPLINE_POSITION[index + 1];          velocityCoef = (d_sup - d_inf) / (t_sup - t_inf);          distanceCoef = d_inf + (t - t_inf) * velocityCoef;        }        mCurrVelocity = velocityCoef * mDistance / mDuration * 1000.0f;        mCurrX = mStartX + Math.round(distanceCoef * (mFinalX - mStartX));        // Pin to mMinX <= mCurrX <= mMaxX        mCurrX = Math.min(mCurrX, mMaxX);        mCurrX = Math.max(mCurrX, mMinX);        mCurrY = mStartY + Math.round(distanceCoef * (mFinalY - mStartY));        // Pin to mMinY <= mCurrY <= mMaxY        mCurrY = Math.min(mCurrY, mMaxY);        mCurrY = Math.max(mCurrY, mMinY);        if (mCurrX == mFinalX && mCurrY == mFinalY) {          mFinished = true;        }        break;      }    }    else {      mCurrX = mFinalX;      mCurrY = mFinalY;      mFinished = true;    }    return true;  }

public void startScroll(int startX, int startY, int dx, int dy) {    startScroll(startX, startY, dx, dy, DEFAULT_DURATION);  } public void startScroll(int startX, int startY, int dx, int dy, int duration) {    mMode = SCROLL_MODE;    mFinished = false;    mDuration = duration;    mStartTime = AnimationUtils.currentAnimationTimeMillis();    mStartX = startX;    mStartY = startY;    mFinalX = startX + dx;    mFinalY = startY + dy;    mDeltaX = dx;    mDeltaY = dy;    mDurationReciprocal = 1.0f / (float) mDuration;  }

public class MoveFreeView extends View{  private int movedX;  private int movedY;  private Scroller mScroller;  public MoveFreeView(Context context) {    super(context);  }  public MoveFreeView(Context context, @Nullable AttributeSet attrs) {    super(context, attrs);    mScroller = new Scroller(context);  }  public MoveFreeView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {    super(context, attrs, defStyleAttr);  }  @Override  public boolean onTouchEvent(MotionEvent event) {    //获取触摸点到边界坐标    int x = (int) event.getX();    int y = (int) event.getY();    switch (event.getAction()){      case MotionEvent.ACTION_DOWN:        movedX = x;        movedY = y;        break;      case MotionEvent.ACTION_MOVE:        int offsetX = x-movedX;        int offsetY = y-movedY;        layout(getLeft()+offsetX,getTop()+offsetY,getRight()+offsetX,getBottom()+offsetY);        break;    }    return super.onTouchEvent(event);  }  //供外界调用通过传递x，y的的滑动距离  public void smoothScrollTo(int destinyX,int destinyY){    //向右侧,下方滑动，请传递负值    int scrollX = getScrollX();    int scrollY = getScrollY();    int delta = destinyX - scrollX;    int deltaY = destinyY - scrollY;    mScroller.startScroll(scrollX,scrollY,delta,deltaY,5000);    invalidate();  }  @Override  public void computeScroll() {    super.computeScroll();    //true则表示滑动未结束    if (mScroller.computeScrollOffset()){      ((View) getParent()).scrollTo(mScroller.getCurrX(),mScroller.getCurrY());      invalidate();    }  }}

private MoveFreeView button;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    button = (MoveFreeView) findViewById(R.id.custon);    button.smoothScrollTo(-400,-300);    //    button.startAnimation(AnimationUtils.loadAnimation(this,R.anim.translate));//    ObjectAnimator animtor1 = ObjectAnimator.ofFloat(button, "translationX", 0, 300);//    ObjectAnimator animtor2 = ObjectAnimator.ofFloat(button, "translationY", 0, 300);//    ObjectAnimator animator3 = ObjectAnimator.ofFloat(button,"rotationX",0.0f,360f);//    ObjectAnimator animator4 = ObjectAnimator.ofFloat(button,"scaleX",1.5f,0.5f);//    AnimatorSet set= new AnimatorSet();//    set.setDuration(5000);//    set.playTogether(animtor1,animtor2,animator3,animator4);//    set.addListener(new Animator.AnimatorListener() {//      @Override//      public void onAnimationStart(Animator animator) {////      }////      @Override//      public void onAnimationEnd(Animator animator) {//        //动画结束时做一些事情//      }////      @Override//      public void onAnimationCancel(Animator animator) {////      }////      @Override//      public void onAnimationRepeat(Animator animator) {////      }//    });//    set.start();  }}