SetAdapter 空指针对象异常

Posted 2023-04-19

【中文标题】SetAdapter 空指针对象异常

【英文标题】：SetAdapter Null pointer Object Exception

【发布时间】：2021-04-22 21:46:25

【问题描述】：

package com.example.shift.adapter;

import android.graphics.Color;
import android.os.Handler;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.constraintlayout.widget.ConstraintLayout;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import androidx.viewpager.widget.ViewPager;

import com.example.shift.R;
import com.example.shift.modal.HomePageModal;
import com.example.shift.modal.HorizontalProductScrollModel;
import com.example.shift.modal.sliderModel;

import org.jetbrains.annotations.NotNull;

import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

public class HomePageAdapter extends RecyclerView.Adapter 

    private List<HomePageModal> homePageModalList;

    public HomePageAdapter(List<HomePageModal> homePageModalList) 
        this.homePageModalList = homePageModalList;
    

    @Override
    public int getItemViewType(int position) 
        switch (homePageModalList.get(position).getType()) 
            case 0:
                return HomePageModal.BANNER_SLIDER;
            case 1:
                return HomePageModal.STRIP_AD_BANNER;
            case 2:
                return HomePageModal.HORIZONTAL_PRODUCT_VIEW;
            case 3:
                return HomePageModal.GRID_PRODUCT_VIEW;
            default:
                return -1;
        
    

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) 
        switch (viewType) 
            case HomePageModal.BANNER_SLIDER:
                View bannerSliderview = LayoutInflater.from(parent.getContext()).inflate(R.layout.slider_layout, parent, false);
                return new BannerSliderViewHolder(bannerSliderview);
            case HomePageModal.STRIP_AD_BANNER:
                View stripAdview = LayoutInflater.from(parent.getContext()).inflate(R.layout.strip_ad_layout, parent, false);
                return new StripAdBannerViewHolder(stripAdview);
            case HomePageModal.HORIZONTAL_PRODUCT_VIEW:
                View horizontalProductView = LayoutInflater.from(parent.getContext()).inflate(R.layout.horizontal_scroll_layout, parent, false);
                return new HorizontalProductViewholder (horizontalProductView);
            case HomePageModal.GRID_PRODUCT_VIEW:
                View gridProductView = LayoutInflater.from(parent.getContext()).inflate(R.layout.grid_product_layout, parent, false);
                return new GridProductViewholder(gridProductView);
            default:
                return null;
        
    

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) 
        switch (homePageModalList.get(position).getType()) 
            case HomePageModal.BANNER_SLIDER:
                List<sliderModel> sliderModelList = homePageModalList.get(position).getSliderModelList();
                ((BannerSliderViewHolder) holder).setBannersliderViewpager(sliderModelList);
                break;
            case HomePageModal.STRIP_AD_BANNER:
                int resource = homePageModalList.get(position).getResource();
                String color = homePageModalList.get(position).getBackgroundColor();
                ((StripAdBannerViewHolder) holder).setStripAd(resource, color);
                break;
            case HomePageModal.HORIZONTAL_PRODUCT_VIEW:
                String HorizontalLayouttitle =homePageModalList.get(position).getTitle();
                List<HorizontalProductScrollModel>horizontalProductScrollModelList =homePageModalList.get(position).getHorizontalProductScrollModelList();
                ((HorizontalProductViewholder) holder).setHorizontalProductLayout(horizontalProductScrollModelList,HorizontalLayouttitle);
                break;
            case HomePageModal.GRID_PRODUCT_VIEW:
                String GridLayouttitle =homePageModalList.get(position).getTitle();
                List<HorizontalProductScrollModel>gridProductScrollModelList =homePageModalList.get(position).getHorizontalProductScrollModelList();
                ((GridProductViewholder) holder).setGridLayout(gridProductScrollModelList,GridLayouttitle);
                break;
            default:
                return;
        
    

    @Override
    public int getItemCount() 
        return homePageModalList.size();
    

    /// Slider List
    public class BannerSliderViewHolder extends RecyclerView.ViewHolder 

        private ViewPager bannersliderViewpager;
        private int currentpage = 2;
        private Timer timer;
        private final long DELAY_TIME = 3000;
        private final long PERIOD_TIME = 3000;

        public BannerSliderViewHolder(@NonNull View itemView) 
            super(itemView);
            bannersliderViewpager = itemView.findViewById(R.id.banner_slider_viewpager);
        

        private void setBannersliderViewpager(final List<sliderModel>sliderModelList)
            SliderAdapter sliderAdapter = new SliderAdapter(sliderModelList);
            bannersliderViewpager.setAdapter(sliderAdapter); **I am getting error at this line **
            bannersliderViewpager.setClipToPadding(false);
            bannersliderViewpager.setPageMargin(20);
            bannersliderViewpager.setCurrentItem(currentpage);

            ViewPager.OnPageChangeListener onPageChangeListener = new ViewPager.OnPageChangeListener() 
                @Override
                public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) 
                

                @Override
                public void onPageSelected(int position) 
                    currentpage = position;
                

                @Override
                public void onPageScrollStateChanged(int state) 
                    if(state == ViewPager.SCROLL_STATE_IDLE)
                        PageLooper(sliderModelList);
                    
                
            ;
            bannersliderViewpager.addOnPageChangeListener(onPageChangeListener);
            startBannerSlideshow(sliderModelList);

            bannersliderViewpager.setOnTouchListener(new View.OnTouchListener() 
                @Override
                public boolean onTouch(View v, MotionEvent event) 
                    PageLooper(sliderModelList);
                    stopBannerSlideshow();
                    if(event.getAction()==MotionEvent.ACTION_UP)
                        startBannerSlideshow(sliderModelList);
                    
                    return false;
                
            );
        
        private void PageLooper(@NotNull List<sliderModel> sliderModelList) 
            if (currentpage == sliderModelList.size() - 2) 
                currentpage = 2;
                bannersliderViewpager.setCurrentItem(currentpage, false);
            

            if (currentpage == 1) 
                currentpage = sliderModelList.size() - 3;
                bannersliderViewpager.setCurrentItem(currentpage, false);
            
        
        private void startBannerSlideshow(List<sliderModel> sliderModelList) 
            Handler handler = new Handler();
            Runnable update = new Runnable() 
                @Override
                public void run() 
                    if (currentpage >= sliderModelList.size()) 
                        currentpage = 1;
                    
                    bannersliderViewpager.setCurrentItem(currentpage++, true);
                
            ;
            timer = new Timer();
            timer.schedule(new TimerTask() 
                @Override
                public void run() 
                    handler.post(update);
                
            , DELAY_TIME, PERIOD_TIME);
        
        private void stopBannerSlideshow() 
            timer.cancel();
        
    

    /// Strip Ad
    public class StripAdBannerViewHolder extends RecyclerView.ViewHolder 
        private ImageView stripAdImage;
        private ConstraintLayout stripAdContainer;

        public StripAdBannerViewHolder(@NonNull View itemView) 
            super(itemView);
            stripAdImage = itemView.findViewById(R.id.strip_ad_image);
            stripAdContainer = itemView.findViewById(R.id.strip_ad_container);
        

        private void setStripAd(int resource, String color) 
            stripAdImage.setImageResource(resource);
            stripAdContainer.setBackgroundColor(Color.parseColor(color));
        
    
    /// Horizontal
    public class HorizontalProductViewholder extends RecyclerView.ViewHolder
        private TextView horizontalLayoutTitle;
        private Button horizontalviewAllbtn;
        private RecyclerView horizontalrecyclerview;
        public HorizontalProductViewholder(@NonNull View itemView) 
            super(itemView);
            horizontalLayoutTitle = itemView.findViewById(R.id.h_s_product_titile);
            horizontalviewAllbtn = itemView.findViewById(R.id.horizontal_scroll_lt_viewAllbtn);
            horizontalrecyclerview = itemView.findViewById(R.id.horizontal_scroll_lt_recyclerview);
        

        private void setHorizontalProductLayout(@NotNull List<HorizontalProductScrollModel> horizontalProductScrollModelList, String title)
            horizontalLayoutTitle.setText(title);

            if(horizontalProductScrollModelList.size() >8 )
                horizontalviewAllbtn.setVisibility(View.VISIBLE);
            else
                horizontalviewAllbtn.setVisibility(View.INVISIBLE);
            
            HorizontalProductScrollAdapter horizontalProductScrollAdapter = new HorizontalProductScrollAdapter(horizontalProductScrollModelList);
            LinearLayoutManager linearLayoutManagerhorizontal = new LinearLayoutManager(itemView.getContext());
            linearLayoutManagerhorizontal.setOrientation(LinearLayoutManager.HORIZONTAL);
            horizontalrecyclerview.setLayoutManager(linearLayoutManagerhorizontal);

            horizontalrecyclerview.setAdapter(horizontalProductScrollAdapter);
            horizontalProductScrollAdapter.notifyDataSetChanged();
        
    
    /// Grid Layout
    public class GridProductViewholder extends RecyclerView.ViewHolder

        private TextView gridLayoutTitle;
        private Button gridLayoutViewAllbtn;
        private GridView gridView;
        public GridProductViewholder(@NonNull View itemView) 
            super(itemView);
            TextView gridLayoutTitle = itemView.findViewById(R.id.grid_product_layout_titile);
            Button gridLayoutViewAllbtn = itemView.findViewById(R.id.grid_product_layout_viewAlbtn);
            GridView gridView = itemView.findViewById(R.id.grid_product_layout_gridView);
        
        private void setGridLayout(List<HorizontalProductScrollModel>horizontalProductScrollAdapterList,String title)
            gridLayoutTitle.setText(title);
            gridView.setAdapter(new gridProductLayoutAdapter(horizontalProductScrollAdapterList));
        
    

[Null object Exception][1]**我收到此错误 java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.viewpager.widget.ViewPager.setAdapter(androidx.viewpager.widget.PagerAdapter)'在空对象引用上 在 com.example.shift.adapter.HomePageAdapter$BannerSliderViewHolder.setBannersliderViewpager(HomePageAdapter.java:124) **

【参考方案1】：

bannersliderViewpager 是使用 itemView.findViewById(R.id.banner_slider_viewpager); 初始化的，当没有具有给定 ID 的视图时，它会返回 null。这会导致您的 NullPointerException，因为您正在调用 null 对象引用上的方法。