Android Metro风格的Launcher开发系列第二篇

这个是通过获取ViewPager的Scroller，对Scroller重新设置一些参数就可以了，具体实现的代码如下：

Field Scroller = ViewPager.class.getDeclaredField("mScroller");
Scroller.setAccessible(true);
Interpolator interpolator = new LinearInterpolator();//设置加速器
ViewPagerScroller scroller = new ViewPagerScroller(context,interpolator);//重新设置ViewPager的Scroller
Scroller.set(this, scroller);

@Override
public void startScroll(int startX, int startY, int dx, int dy) {
    // Ignore received duration, use fixed one instead
    super.startScroll(startX, startY, dx, dy, mDuration);
}
 
@Override
public void startScroll(int startX, int startY, int dx, int dy, int duration) {
    // Ignore received duration, use fixed one instead
    super.startScroll(startX, startY, dx, dy, mDuration);
}

class LauncherPageTransformer implements ViewPager.PageTransformer {
    private static float DEFAULT_SCALE = 1.0f;
    private static float SCALE_FACTOR = 0.30f;// 缩放因子 0.50f
    private static float ROTATION_FACTOR = 20f;// 旋转因子
    private static float ALPHA_FACTOR = 0.8f;
 
    @Override
    public void transformPage(View view, float position) {
        if (position <= 1) { // [-1,1]
            // Modify the default slide transition to shrink the page as well
            if (position < 0) {
                // view.setRotationY(position * ROTATION_FACTOR);
                view.setScaleX(SCALE_FACTOR * position + DEFAULT_SCALE);
                view.setScaleY(SCALE_FACTOR * position + DEFAULT_SCALE);
                // view.setAlpha(ALPHA_FACTOR * position + 1.0f);
            } else {
                // view.setRotationY(position * ROTATION_FACTOR);
                view.setScaleX(SCALE_FACTOR * -position + DEFAULT_SCALE);
                view.setScaleY(SCALE_FACTOR * -position + DEFAULT_SCALE);
                // view.setAlpha(ALPHA_FACTOR * -position + 1.0f);
            }
        }
    }
 
}

public class LauncherViewPager extends ViewPager {
    public static final int PAGE_LIMIT = 3;
 
    public LauncherViewPager(Context context) {
        this(context, null);
    }
 
    public LauncherViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }
 
    private void init(Context context) {
        this.setPageMargin(-getResources().getInteger(R.integer.portal_viewpager_margin));
        this.setOffscreenPageLimit(PAGE_LIMIT);
        this.setPageTransformer(true, new LauncherPageTransformer());
        try {
            Field Scroller = ViewPager.class.getDeclaredField("mScroller");
            Scroller.setAccessible(true);
            Interpolator interpolator = new LinearInterpolator();
            ViewPagerScroller scroller = new ViewPagerScroller(context,
                    interpolator);
            Scroller.set(this, scroller);
        } catch (NoSuchFieldException e) {
        } catch (IllegalArgumentException e) {
        } catch (IllegalAccessException e) {
        }
    }
}

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