fragment和viewpager

在app首頁中我們經常會看到滑動的歡迎界面，和介紹頁面，在一個activity或是fragment中實現多圖片或多見面，下面我們介紹下fragment和viewpager的實現

看源碼

<span style="font-size:14px;">public class CreateCardNewFragment extends BaseFragment  {
   
    private List<View> mPagers = new ArrayList<>();
   
    private ViewPager mViewPager;
   
    private SplashViewAdapter adapter;
   
    private int[] mViewPagerImages = new int[]{
            R.drawable.bg_create_card_one_show,
            R.drawable.icon_create_card_two, R.drawable.icon_create_card_three,
            R.drawable.icon_create_card_four, R.drawable.bg_create_card_five,
            R.drawable.bg_create_card_six, R.drawable.icon_create_card_seven
    };
  

  
    protected  View onCreateView(LayoutInflater inflater, ViewGroup container,
                                   Bundle savedInstanceState) {
      
        View view = View.inflate(getActivity(), R.layout.view_splash_view_pager, null);
        mViewPager = (ViewPager) view.findViewById(R.id.fl_welcome_view);
        mViewPager.setOnPageChangeListener(mPageListener);
        setPagers();
        adapter = new SplashViewAdapter(mPagers);
        mViewPager.setAdapter(adapter);
    }


    private void setPagers() {
        viewTwo = getImageView();
        viewThree = getImageView();
        viewFour = getImageView();
        mPagers.add(viewTwo);
        mPagers.add(viewThree);
        mPagers.add(viewFour);
        
    }


    private ImageView getImageView() {
        ImageView mImageView = new ImageView(getActivity());
        return mImageView;
    }

   

    private ViewPager.SimpleOnPageChangeListener mPageListener = new ViewPager.SimpleOnPageChangeListener() {
        @Override
        public void onPageSelected(int position) {
            mPosition = position;
         //滑動屏幕
           
        }
    };


    /**
     * 適配器
     */
    public class SplashViewAdapter extends PagerAdapter {

        private List<View> list;

        SplashViewAdapter(List<View> list) {
            this.list = list;
        }

        public void setViewList(List<View> viewList) {
            this.list = viewList;
            notifyDataSetChanged();
        }

        @Override

        public int getItemPosition(Object object) {
            return POSITION_NONE;

        }

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

        @Override
        public boolean isViewFromObject(View view, Object o) {
            return view == o;
        }

        private Bitmap getBitMap(int position) {
            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inPreferredConfig = Bitmap.Config.RGB_565;
            options.inInputShareable = true;
            //options.inSampleSize = 2;
            options.inPurgeable = true;
            InputStream in;
                in = getResources().openRawResource(mViewPagerImages[position]);
                bitmap = BitmapFactory.decodeStream(in, null, options);
                return bitmap;
                in = getResources().openRawResource(mViewPagerImages[position + 1]);
                Bitmap mBitmap = BitmapFactory.decodeStream(in, null, options);
                return mBitmap;
            }
        }
      //創建顯示界面
        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            View view = list.get(position);
            view.setBackgroundDrawable(new BitmapDrawable(getBitMap(position)));
            container.addView(view);
            return view;
        }
      //回收界面
        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            container.removeView((View) object);
            if (isFirstView) {
                isFirstView = false;
            } else {
                if (object instanceof ImageView) {
                    ImageView imageView = (ImageView) object;
                    WeakReference<Bitmap> weakReference = new WeakReference<>
                            (((BitmapDrawable) imageView.getBackground()).getBitmap());
                    if (weakReference != null && weakReference.get() != null && !weakReference.get().isRecycled()) {
                        weakReference.get().recycle();
                    }
                }
            }
        }
    }
}</span>

ViewPager 的layout

<span style="font-size:14px;"><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffff">

    <android.support.v4.view.ViewPager
        android:id="@+id/fl_welcome_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v4.view.ViewPager>
</RelativeLayout></span>

     總結：在我們應用viewpager時內存溢出無疑是大家頭疼的事情，一旦超過了5張左右的大圖，那麼就很容易出現溢出，所有上面我在代碼中把界面的創建放在了instantiateItem（）方法當中，每次需要的時候纔去加載創建對應的界面，這樣避免了一次性加載全部的圖片導致溢出，在destroyItem（）方法裏面去回收沒有用到的圖片或佈局，從而保證內存不溢出；