Android开发banner上下滚动轮播

一、效果图

banner一般不是左右滚动嘛？现在可以上下滚动，折叠滚动，放大缩小滚动等等
具体可以看https://www.bilibili.com/video/BV1jK4y1G78Z/

二、思路

主要是自定义PageTransformer 然后进行mViewPager.setPageTransformer。设置viewpager的切换效果
引入：implementation 'com.github.Achenglove:AchengImageSliders:v1.0.2'

三、上下滚动自定义PageTransformer关键代码

public abstract class BaseTransformer implements PageTransformer {
private BaseAnimationInterface mCustomAnimationInterface;
private HashMap<View, ArrayList<Float>> h = new HashMap();
boolean isApp;
boolean isDis;

public BaseTransformer() {
}

protected abstract void onTransform(View var1, float var2);

public void transformPage(View view, float position) {
    this.onPreTransform(view, position);
    this.onTransform(view, position);
    this.onPostTransform(view, position);
}

protected boolean hideOffscreenPages() {
    return true;
}

protected boolean isPagingEnabled() {
    return false;
}

protected void onPreTransform(View view, float position) {
    float width = (float)view.getWidth();
    ViewHelper.setRotationX(view, 0.0F);
    ViewHelper.setRotationY(view, 0.0F);
    ViewHelper.setRotation(view, 0.0F);
    ViewHelper.setScaleX(view, 1.0F);
    ViewHelper.setScaleY(view, 1.0F);
    ViewHelper.setPivotX(view, 0.0F);
    ViewHelper.setPivotY(view, 0.0F);
    ViewHelper.setTranslationY(view, 0.0F);
    ViewHelper.setTranslationX(view, this.isPagingEnabled() ? 0.0F : -width * position);
    if (this.hideOffscreenPages()) {
        ViewHelper.setAlpha(view, position > -1.0F && position < 1.0F ? 1.0F : 0.0F);
    } else {
        ViewHelper.setAlpha(view, 1.0F);
    }

    if (this.mCustomAnimationInterface != null && (!this.h.containsKey(view) || ((ArrayList)this.h.get(view)).size() == 1) && position > -1.0F && position < 1.0F) {
        if (this.h.get(view) == null) {
            this.h.put(view, new ArrayList());
        }

        ((ArrayList)this.h.get(view)).add(position);
        if (((ArrayList)this.h.get(view)).size() == 2) {
            float zero = (Float)((ArrayList)this.h.get(view)).get(0);
            float cha = (Float)((ArrayList)this.h.get(view)).get(1) - (Float)((ArrayList)this.h.get(view)).get(0);
            if (zero > 0.0F) {
                if (cha > -1.0F && cha < 0.0F) {
                    this.mCustomAnimationInterface.onPrepareNextItemShowInScreen(view);
                } else {
                    this.mCustomAnimationInterface.onPrepareCurrentItemLeaveScreen(view);
                }
            } else if (cha > -1.0F && cha < 0.0F) {
                this.mCustomAnimationInterface.onPrepareCurrentItemLeaveScreen(view);
            } else {
                this.mCustomAnimationInterface.onPrepareNextItemShowInScreen(view);
            }
        }
    }

}

protected void onPostTransform(View view, float position) {
    if (this.mCustomAnimationInterface != null) {
        if (position != -1.0F && position != 1.0F) {
            if (position == 0.0F) {
                this.mCustomAnimationInterface.onNextItemAppear(view);
                this.isDis = true;
            }
        } else {
            this.mCustomAnimationInterface.onCurrentItemDisappear(view);
            this.isApp = true;
        }

        if (this.isApp && this.isDis) {
            this.h.clear();
            this.isApp = false;
            this.isDis = false;
        }
    }

}

public void setCustomAnimationInterface(BaseAnimationInterface animationInterface) {
    this.mCustomAnimationInterface = animationInterface;
}
}

VerticalTransformer：上下滚动

public class VerticalTransformer extends BaseTransformer {
@Override
protected void onTransform(View view, float position) {


    ViewHelper.setPivotY(view, position < 0.0F ? 0.0F : (float)view.getHeight());
    //ViewHelper.setScaleY(view, position < 0.0F ? 1.0F + position : 1.0F - position);
    ViewHelper.setTranslationY(view, (float)view.getHeight() * position);
}



@Override
protected boolean isPagingEnabled() {
    return false;
}


}

有兴趣看其他banner切换效果的，请看我上面的视频链接。