androidx viewpager2的使用详解

在Android 中,像常用的控件:TextView \ EditText \ Button\ImageView\ViewPager\RadioGroup\RadioButton\Switch\CheckBox等等

这些大多数都是很有历史的控件了,我们接下来将一下一个全新的控件:

ViewPager2

在没推出androidx之前,android生态有些混乱,自从Google官方开始重视这一问题以后 就有了后续的jetpack和一系列的控件

viewpager 我们一般是exends PageAdapter或者其他的适配器,完成不通类型之间页面滑动 A--->B---->C  默认会缓存2个页面的数据,有个缓存设计,也就是当前在B页面---C页面的数据会初始化,所以才有了懒加载(Fragment)

懒加载原理请移步---------> https://blog.csdn.net/qq_29769851/article/details/90712756

先看看ViewPager2的源码:

继承自ViewGroup

setAdapter

/**
 * <p>Set a new adapter to provide page views on demand.</p>
 *
 * <p>If you're planning to use {@link androidx.fragment.app.Fragment Fragments} as pages,
 * implement {@link androidx.viewpager2.adapter.FragmentStateAdapter FragmentStateAdapter}. If
 * your pages are Views, implement {@link RecyclerView.Adapter} as usual.</p>
 *
 * <p>If your pages contain LayoutTransitions, then those LayoutTransitions <em>must</em> have
 * {@code animateParentHierarchy} set to {@code false}. Note that if you have a ViewGroup with
 * {@code animateLayoutChanges="true"} in your layout xml file, a LayoutTransition is added
 * automatically to that ViewGroup. You will need to manually call {@link
 * android.animation.LayoutTransition#setAnimateParentHierarchy(boolean)
 * getLayoutTransition().setAnimateParentHierarchy(false)} on that ViewGroup after you inflated
 * the xml layout, like this:</p>
 *
 * <pre>
 * View view = layoutInflater.inflate(R.layout.page, parent, false);
 * ViewGroup viewGroup = view.findViewById(R.id.animated_viewgroup);
 * viewGroup.getLayoutTransition().setAnimateParentHierarchy(false);
 * </pre>
 *
 * @param adapter The adapter to use, or {@code null} to remove the current adapter
 * @see androidx.viewpager2.adapter.FragmentStateAdapter
 * @see RecyclerView#setAdapter(Adapter)
 */
public void setAdapter(@Nullable @SuppressWarnings("rawtypes") Adapter adapter) {
    final Adapter<?> currentAdapter = mRecyclerView.getAdapter();
    mAccessibilityProvider.onDetachAdapter(currentAdapter);
    unregisterCurrentItemDataSetTracker(currentAdapter);
    mRecyclerView.setAdapter(adapter);
    mCurrentItem = 0;
    restorePendingState();
    mAccessibilityProvider.onAttachAdapter(adapter);
    registerCurrentItemDataSetTracker(adapter);
}

描述的意思 大概是使用RecyclerView 的 dapter,在了解了使用方法以后,于是就开始体验一下吧!

@FindView(R.id.splash_viewpage2)
ViewPager2 viewPager2;

设置滑动方向  ---> 左右或者上下

viewPager2.setOrientation(ViewPager2.ORIENTATION_HORIZONTAL);

ViewPager2的Adapter

public class SplashAdapter extends RecyclerView.Adapter<SplashAdapter.SplashVH> {

    private List<SplashImageBean> list;

    public SplashAdapter(List<SplashImageBean> list) {
        this.list = list;
    }

    @NonNull
    @Override
    public SplashVH onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = ((LayoutInflater)parent.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE))
                .inflate(R.layout.item_splash_wellcome,parent,false);
        return new SplashVH(view);
    }

    @Override
    public void onBindViewHolder(@NonNull SplashVH holder, int position) {
        holder.iv_splash_image_center.setBackgroundResource(list.get(position).getIcon());
//        holder.imageView.startCountDown();
    }

    @Override
    public int getItemCount() {
        return list == null ? 0 : list.size();
    }

    static class SplashVH extends RecyclerView.ViewHolder{
        private ImageView iv_splash_image_center;
        private CountDownView countDownView;
        public SplashVH(@NonNull View itemView) {
            super(itemView);
            this.iv_splash_image_center = itemView.findViewById(R.id.iv_splash_image_center);
            countDownView = itemView.findViewById(R.id.cdv_splash_number);
        }
    }

那么 跟之前的 ViewPager有些API变更 比如 addOnPageChange  现已经更换为:

registerOnPageChangeCallback

Code:

viewPager2.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {
    @Override
    public void onPageSelected(int position) {
        if (position == list.size()-1){
            btn_splash_start.setVisibility(View.VISIBLE);
            btn_splash_start.startAnimation(animation);
        }else{
            btn_splash_start.setVisibility(View.GONE);
        }
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        super.onPageScrolled(position, positionOffset, positionOffsetPixels);
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        super.onPageScrollStateChanged(state);
    }
    
});