Android开发艺术笔记 | View的滑动（三种普遍实现方式及其对比、实战）

    /**
      * Set the scrolled position of your view. This will cause a call to
      * {@link #onScrollChanged(int,int,int,int)} and the view will be
      * invalidated.
      * @param x the x position to scroll to
      * @param y the y position to scroll to
      */
    public void scrollTo(int x,int y) {
        if (mScrollX != x || mScrollY != y) {
                int oldX = mScrollX;
                int oldY = mScrollY;
                mScrollX = x;
                mScrollY = y;
                invalidateParentCaches();
                onScrollChanged(mScrollX,mScrollY,oldX,oldY);
                if (!awakenScrollBars()) {
                        postInvalidateOnAnimation();
                }
        }
    }
     /**
      * Move the scrolled position of your view. This will cause a call to
      * {@link #onScrollChanged(int,int,int,int)} and the view will be
      * invalidated.
      * @param x the amount of pixels to scroll by horizontally
      * @param y the amount of pixels to scroll by vertically
      */
    public void scrollBy(int x,int y) {
        scrollTo(mScrollX + x,mScrollY + y);
    }

    <?xml version="1.0" encoding="utf-8"?>
    <set xmlns:android="http://schemas.android.com/apk/res/android"
         android:fillAfter="true"
         android:zAdjustment="normal" >
         <translate
             android:duration="100"
             android:fromXDelta="0"
             android:fromYDelta="0"
             android:interpolator="@android:anim/linear_interpolator"
             android:toXDelta="100"
             android:toYDelta="100" />
    </set>

ObjectAnimator.ofFloat(targetView,"translationX",0,100).setDuration(100).start();

- View动画是对View的影像做操作， 并不能真正改变View的位置参数，包括宽/高，
 并且如果希望动画后的状态得以保留还必须将fillAfter属性设置为true，
 否则动画完成后动画结果会消失。
    - 使用属性动画并不会存在上述问题，
 但是在Android 3.0以下无法使用属性动画，
 需使用动画兼容库nineoldandroids来实现属性动画，
 不过，
 在Android 3.0以下的手机上通过nineoldandroids来实现的属性动画
 本质上仍然是View动画。同时View动画还有一个很严重的问题，
比如我们通过View动画将一个Button向右移动100px，
并且这个View设置的有单击事件，
这样子单击新位置无法触发onClick事件，
而单击原始位置仍然可以触发onClick事件，
尽管Button已经不在原始位置了。

MarginLayoutParams params = (MarginLayoutParams)mButton1.getLayoutParams();
params.width += 100;
params.leftMargin += 100;
mButton1.requestLayout();//或mButton1.setLayoutParams(params);

public class DragView4 extends View {

    private int lastX;
    private int lastY;

    public DragView4(Context context) {
        super(context);
        ininView();
    }

    public DragView4(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
    }

    public DragView4(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        ininView();
    }

    private void ininView() {
        setBackgroundColor(Color.BLUE);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastX = (int) event.getX();
                lastY = (int) event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                int offsetX = x - lastX;
                int offsetY = y - lastY;
                ((View) getParent()).scrollBy(-offsetX, -offsetY);
                break;
        }
        return true;
    }
}

public class DragView3 extends View {

    private int lastX;
    private int lastY;

    public DragView3(Context context) {
        super(context);
        ininView();
    }
    public DragView3(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
    }
    public DragView3(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        ininView();
    }

    private void ininView() {
        setBackgroundColor(Color.BLUE);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                // 记录触摸点坐标
                lastX = (int) event.getX();
                lastY = (int) event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                // 计算偏移量
                int offsetX = x - lastX;
                int offsetY = y - lastY;

                ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) getLayoutParams();
//                LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) getLayoutParams();
                layoutParams.leftMargin = getLeft() + offsetX;
                layoutParams.topMargin = getTop() + offsetY;
                setLayoutParams(layoutParams);
                break;
        }
        return true;
    }
}