ViewPager（二）动态获取Item

绝地灬酷狼 2022-05-26 00:41 214阅读 0赞

很多时候需要ViewPager可以动态的加载图片，数据分页拉取，这个时候不能notifyDateSetChanged，会回到第0个Item的位置，一种实现思路是建立一个非常大的空数组（元素为null）容量很大，拉取的数据可以填充到里面，这样实现动态的拉取，自己实现了一个。代码如下，首先是Activity

package com.xue.qin.mygallery.activity;
    
    import android.app.Activity;
    import android.content.Intent;
    import android.os.Bundle;
    import android.support.annotation.Nullable;
    
    import com.xue.qin.mygallery.R;
    import com.xue.qin.mygallery.adapter.UnlimitedAdapter;
    import com.xue.qin.mygallery.interfaces.DataProvider;
    import com.xue.qin.mygallery.views.UnlimitedViewPager;
    
    import java.util.ArrayList;
    
    /**
     * Created by xue.qin on 2018/4/21.
     */
    
    public class UnlimitedActivity extends Activity implements DataProvider {
        private UnlimitedViewPager mUnlimitViewPager;
        private UnlimitedAdapter mUnlimitAdapter;
        private ArrayList<String> mData;
        private int left;
        private int right;
        private int current;
    
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            Intent intent = getIntent();
            mData = intent.getStringArrayListExtra(GridActivity.DATA);
            current = intent.getIntExtra(GridActivity.CURRENT, 0);
            left = current - 1;
            right = current + 1;
            String initUri = mData.get(current);
            setContentView(R.layout.pager_unlimited_acitvity_layout);
            mUnlimitViewPager = (UnlimitedViewPager) findViewById(R.id.viewPager);
            mUnlimitAdapter = new UnlimitedAdapter(this, mUnlimitViewPager, initUri, this);
            mUnlimitViewPager.setAdapter(mUnlimitAdapter);
            mUnlimitAdapter.scrolltoCurrent();
        }
    
        @Override
        public String getLeft() {
            if (left < 0) {
                return null;
            }
            String uri = mData.get(left);
            left--;
            return uri;
        }
    
        @Override
        public String getRight() {
            if (right > mData.size() - 1) {
                return null;
            }
            String uri = mData.get(right);
            right++;
            return uri;
        }
    
        @Override
        public ArrayList<String> getLeftArray() {
            return null;
        }
    
        @Override
        public ArrayList<String> getRightArrAy() {
            return null;
        }
    }

ViewPager

package com.xue.qin.mygallery.views;
    
    /**
     * Created by xue.qin on 2018/4/21.
     */
    import android.content.Context;
    import android.util.AttributeSet;
    import android.view.MotionEvent;
    /**
     * Created by qinxue on 2018/1/15.
     */
    
    public class UnlimitedViewPager extends HackyViewPager {
        private int mLeftPosition;
        private int mRightPosition;
        private int mWidth;
        private float mLastX = -1;
    
        public UnlimitedViewPager(Context context, AttributeSet attrs) {
            super(context, attrs);
        }
    
        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            mWidth = getClientWidth();
        }
    
        @Override
        public boolean onInterceptTouchEvent(MotionEvent ev) {
            float x = ev.getX();
            float dx = x - mLastX;
            mLastX = x;
            if (getCurrentItem() == mRightPosition && dx < 0 || getCurrentItem() == mLeftPosition && dx > 0) {
                return false;
            }
            return super.onInterceptTouchEvent(ev);
        }
    
        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX();
            float dx = x - mLastX;
            mLastX = x;
            if (getCurrentItem() == mRightPosition && dx < 0 || getCurrentItem() == mLeftPosition && dx > 0) {
                return true;
            }
            return super.onTouchEvent(event);
        }
    
        @Override
        public boolean dispatchTouchEvent(MotionEvent ev) {
            if (ev.getAction() == MotionEvent.ACTION_DOWN) {
                mLastX = ev.getX();
            }
            return super.dispatchTouchEvent(ev);
        }
    
        public void setRealLeftPosition(int leftPosition) {
            mLeftPosition = leftPosition;
        }
    
        public void setRealRightPosition(int rightPosition) {
            mRightPosition = rightPosition;
        }
    
        private int getClientWidth() {
            return getMeasuredWidth() - getPaddingLeft() - getPaddingRight();
        }
    }

Adapter

package com.xue.qin.mygallery.adapter;
    
    import android.content.Context;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ImageView;
    
    import com.bumptech.glide.Glide;
    import com.bumptech.glide.load.engine.DiskCacheStrategy;
    import com.xue.qin.mygallery.R;
    import com.xue.qin.mygallery.interfaces.DataProvider;
    import com.xue.qin.mygallery.views.UnlimitedViewPager;
    
    import java.util.ArrayList;
    
    /**
     * Created by xue.qin on 2018/4/21.
     */
    
    public class UnlimitedAdapter extends android.support.v4.view.PagerAdapter {
        private static final int MAX_CAPACITY = 10000;
        private Context mContext;
        private String[] mData = new String[MAX_CAPACITY];
        private LayoutInflater mInflater;
        private UnlimitedViewPager mViewPager;
        private int initCursot = MAX_CAPACITY / 2;
        private int leftCursor = MAX_CAPACITY / 2 - 1;
        private int rightCursor = MAX_CAPACITY / 2 + 1;
        private DataProvider mDataProvider;
    
        public UnlimitedAdapter(Context context, UnlimitedViewPager viewPager, String initUri, DataProvider dataProvider) {
            mContext = context;
            mInflater = LayoutInflater.from(mContext);
            mDataProvider = dataProvider;
            mViewPager = viewPager;
            init(initUri);
        }
    
        private void init(String initUri) {
            mData[initCursot] = initUri;
            addLeft(mDataProvider.getLeft());
            addRight(mDataProvider.getRight());
        }
    
        public void scrolltoCurrent() {
            mViewPager.setCurrentItem(initCursot);
        }
    
        @Override
        public int getCount() {
            return mData.length;
        }
    
        @Override
        public boolean isViewFromObject(View view, Object object) {
            return view == object;
        }
    
        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            updateData(position);
            if (mData[position] != null) {
                View view = mInflater.inflate(R.layout.pager_adapter_item, null, false);
                ImageView imageView = (ImageView) view.findViewById(R.id.imageView);
                Glide.with(mContext)
                        .load(mData[position])
                        .diskCacheStrategy(DiskCacheStrategy.SOURCE)
                        .into(imageView);
                container.addView(view);
                return view;
            } else {
                return null;
            }
        }
    
        private void updateData(int position) {
            String uri = null;
            if (position == leftCursor + 1) {
                uri = mDataProvider.getLeft();
                if (uri != null) {
                    addLeft(uri);
                } else {
                    mViewPager.setRealLeftPosition(position);
                }
            } else if (position == rightCursor - 1) {
                uri = mDataProvider.getRight();
                if (uri != null) {
                    addRight(uri);
                } else {
                    mViewPager.setRealRightPosition(position);
                }
            }
        }
    
        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            container.removeView((View) object);
        }
    
        public void addLeft(String uri) {
            if (leftCursor == 0 || uri == null) {
                mViewPager.setRealLeftPosition(leftCursor + 1);
                return;
            }
            mData[leftCursor] = uri;
            leftCursor--;
        }
    
        public void addRight(String uri) {
            if (rightCursor == MAX_CAPACITY - 1 || uri == null) {
                mViewPager.setRealRightPosition(rightCursor - 1);
            }
            mData[rightCursor] = uri;
            rightCursor++;
        }
    
        public void addLeft(ArrayList<String> uris) {
            for (String uri : uris) {
                mData[leftCursor] = uri;
                leftCursor--;
                if (leftCursor < 0) {
                    mViewPager.setRealLeftPosition(leftCursor);
                    break;
                }
            }
        }
    
        public void addRight(ArrayList<String> uris) {
            for (String uri : uris) {
                mData[rightCursor] = uri;
                rightCursor++;
                if (rightCursor > MAX_CAPACITY - 1) {
                    mViewPager.setRealRightPosition(rightCursor);
                    break;
                }
            }
        }
    }

Demo地址：https://github.com/xueqin123/viewpageroom

[点击打开链接][Link 1]

[Link 1]: https://github.com/xueqin123/viewpageroom