Android Adapter代码片

Posted 2020-07-15 狂奔的小狮子

 /**
     * Adapter for grid of coupons.
     */
    private static class CouponAdapter extends BaseAdapter {

        private LayoutInflater mInflater;
        private List<Coupon> mAllCoupons;

        /**
         * Constructs a new {@link CouponAdapter}.
         *
         * @param inflater to create new views
         * @param allCoupons for list of all coupons to be displayed
         */
        public CouponAdapter(LayoutInflater inflater, List<Coupon> allCoupons) {
            if (allCoupons == null) {
                throw new IllegalStateException("Can‘t have null list of coupons");
            }
            mAllCoupons = allCoupons;
            mInflater = inflater;
        }

        @Override
        public int getCount() {
            return mAllCoupons.size();
        }

        @Override
        public Coupon getItem(int position) {
            return mAllCoupons.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            //缓存策略的另外一种写法

            View result = convertView;
            if (result == null) {
                //注意mInflater的来源，是在Activity的setContextView中这样写的：
                            // Fetch the {@link LayoutInflater} service so that new views can be created
                            //  LayoutInflater inflater = (LayoutInflater) getSystemService(
                            //                                        Context.LAYOUT_INFLATER_SERVICE);
                result = mInflater.inflate(R.layout.grid_item, parent, false);
            }

            // Try to get view cache or create a new one if needed
            ViewCache viewCache = (ViewCache) result.getTag();
            if (viewCache == null) {
                viewCache = new ViewCache(result);
                result.setTag(viewCache);
            }

            // Fetch item
            Coupon coupon = getItem(position);

            // Bind the data
            viewCache.mTitleView.setText(coupon.mTitle);
            viewCache.mSubtitleView.setText(coupon.mSubtitle);
            viewCache.mImageView.setImageURI(coupon.mImageUri);

            return result;
        }
    }

    /**
     * Cache of views in the grid item view to make recycling of views quicker. This avoids
     * additional {@link View#findViewById(int)} calls after the {@link ViewCache} is first
     * created for a view. See
     * {@link CouponAdapter#getView(int position, View convertView, ViewGroup parent)}.
     */
    private static class ViewCache {

        /** View that displays the title of the coupon */
        private final TextView mTitleView;

        /** View that displays the subtitle of the coupon */
        private final TextView mSubtitleView;

        /** View that displays the image associated with the coupon */
        private final ImageView mImageView;

        /**
         * Constructs a new {@link ViewCache}.
         *
         * @param view which contains children views that should be cached.
         */
        private ViewCache(View view) {
            mTitleView = (TextView) view.findViewById(R.id.title);
            mSubtitleView = (TextView) view.findViewById(R.id.subtitle);
            mImageView = (ImageView) view.findViewById(R.id.image);
        }
    }

    /**
     * 关于适配器里面数据bean对象问题，如果只是纯粹展示，而不需要改变bean对象的属性，那么推荐下面这种方式，如果需要改变                      
     * bean对象的属性，那么还是用常见的get set方法实现.
     */
    private static class Coupon {

        /** Title of the coupon. */
        private final String mTitle;

        /** Description of the coupon. */
        private final String mSubtitle;

        /** Content URI of the image for the coupon. */
        private final Uri mImageUri;

        /**
         * Constructs a new {@link Coupon}.
         *
         * @param titleString is the title
         * @param subtitleString is the description
         * @param imageAssetFilePath is the file path from the application‘s assets folder for
         *                           the image associated with this coupon
         */
        private Coupon(String titleString, String subtitleString, String imageAssetFilePath) {
            mTitle = titleString;
            mSubtitle = subtitleString;
            mImageUri = Uri.parse("content://" + AssetProvider.CONTENT_URI + "/" +
                    imageAssetFilePath);
        }
    }