Android ListView 分页加载

     拥有ScrollBar组件中不能在嵌套ScrollBar组件，譬如ScrollView组件里面不能嵌套ListView或者是GridView，这个在源码里面就有这样的解释，因为这样是不科学的，存在两个可以滑动的组件的时候，将会出现滑动混淆的情况，譬如我想滑动里面的ListView的时候，那么现在外面的GridView是否选择滑动呢，系统不好判断，所以在Androdi中是不能嵌套两个ScrollBar。

     混淆下拉的事件导致的后果将是只显示一两行的数据，解决方法是，先让子控件的内容全部显示出来，然后禁用子控件的滑动，如果超过了父控件的范围，则显示父控件ScrollBar滚动显示内容，自定义GridView代码:

public class MyGridView extends GridView{public MyGridView(android.content.Context context,android.util.AttributeSet attrs){super(context, attrs);}/** * 设置不滚动 */public void onMeasure(int widthMeasureSpec, int heightMeasureSpec){int expandSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2,MeasureSpec.AT_MOST);super.onMeasure(widthMeasureSpec, expandSpec);}}

自定义的GridView有一个回调方法onMeasure()，主要是用来绘制View显示的宽度与高度，MeasureSpec.makMeasureSpec()方法的第一个参数是决定布局空间的大小，第二个参数是布局模式

MeasureSpec.AT_MOST 的意思是子控件需要多大的空间，就扩展到多大的空间，之后在ScrollView中

添加这个组件就行了，同样有ScrollBar控件的视图控件都适用 ListView等等。

ListView分页加载

image_list.setOnScrollListener(new AbsListView.OnScrollListener() {            public void onScrollStateChanged(AbsListView view, int scrollState) {            }            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {                if(expendable && firstVisibleItem + visibleItemCount == totalItemCount){                    expendable = false;                            anim.start();                    new Thread(new Runnable() {                        public void run() {                            JSONObject result = HttpManager.getInstance().excuteAction(                                ClassHomeActivity.this,                                30450,                                new Pair("ClassId", classId),                                new Pair("PageSize", pageSize),                                new Pair("PageIndex", pageIndex++),                                new Pair("AlbumId", 0),                                new Pair("RefreshTime", time),                                new Pair("RefreshType", 2));                            if(result != null){                                final JSONArray items = result.optJSONArray("List");                                if(items.length() != 0){                                    new Handler(Looper.getMainLooper()).post(new Runnable() {                                        public void run() {                                            for(int i = 0; i < items.length(); i++){                                                list.put(items.optJSONObject(i));                                            }                                            smallAdapter.notifyDataSetChanged();                                            bigAdapter.notifyDataSetChanged();                                            if(items.length() == pageSize){                                                expendable = true;                                            }else{                                                photo_loading.setVisibility(View.GONE);                                            }                                        }                                    });                                }                            }                            new Handler(Looper.getMainLooper()).post(new Runnable() {                                public void run() {                                    anim.stop();                                }                            });                        }                    }).start();                }            }        });

listView.setOnScrollListener()事件有两个必须实现的接口，源码中对两个接口的解释:

public interface OnScrollListener {        /**         * The view is not scrolling. Note navigating the list using the trackball counts as         * being in the idle state since these transitions are not animated.         */        public static int SCROLL_STATE_IDLE = 0;        /**         * The user is scrolling using touch, and their finger is still on the screen         */        public static int SCROLL_STATE_TOUCH_SCROLL = 1;        /**         * The user had previously been scrolling using touch and had performed a fling. The         * animation is now coasting to a stop         */        public static int SCROLL_STATE_FLING = 2;        /**         * Callback method to be invoked while the list view or grid view is being scrolled. If the         * view is being scrolled, this method will be called before the next frame of the scroll is         * rendered. In particular, it will be called before any calls to         * {@link Adapter#getView(int, View, ViewGroup)}.         *         * @param view The view whose scroll state is being reported         *         * @param scrollState The current scroll state. One of {@link #SCROLL_STATE_IDLE},         * {@link #SCROLL_STATE_TOUCH_SCROLL} or {@link #SCROLL_STATE_IDLE}.         */        public void onScrollStateChanged(AbsListView view, int scrollState);        /**         * Callback method to be invoked when the list or grid has been scrolled. This will be         * called after the scroll has completed         * @param view The view whose scroll state is being reported         * @param firstVisibleItem the index of the first visible cell (ignore if         *        visibleItemCount == 0)         * @param visibleItemCount the number of visible cells         * @param totalItemCount the number of items in the list adaptor         */        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,                int totalItemCount);    }

onScrollStateChanged(),onScroll()两个方法，第一个方法的参数为回调方法被调用时，列表视图或网格视图中滚动。如果滚动视图，这个方法会被调用前的下一帧的滚动渲染。特别是，它会被调用之前调用

第二个参数是滚动的状态，0==不滚动的状态，1==用户此前一直滚动使用触摸，并进行了一击。动画现在滑行停止

2==用户此前一直滚动使用触摸，并进行了一击。动画现在滑行停止

其实上面的都是用中英文翻译翻译出来的，当屏幕停止滚动时==0，当屏幕滚动的时候，用户的手指还在屏幕上的时候==1，当用户操作，由于惯性还在滚动的时候==2

onScroll()方法的参数firstVisibableItem表示在现时屏幕第一个ListItem(部分显示的ListItem也算)整个listView

的位置，下标从0开始

VisiableItemCount表示表示在现时屏幕可以见到(部分能够见到的Item也算)总数

totalItem表示总共的ListView中Item项目的总和

判断ListView是否已经滑动到了底部的最好方法是totalItem=firstVisiableItem+visiableItemCount,此时的ListView是滑动到了底部的，但是并不是每一次滑动到了底部都会加载新的动画，expendable变量的作用是用来防止ListView往上滑动的时候也出现正在加载的动画，因为也会出发onScroll方法，所以用一个标志性的变量来保存是否加载底部动画显示正在加载的footer View。加载完毕之后刷新ListView的数据，然后设置动画隐藏