listview的重要属性viewtype，实现多类型item样式

来源：互联网发布：linux session 编辑：程序博客网时间：2024/05/17 01:08

listview作为传统展示大量数据的基本控件，其回收能力是核心。考虑到数据并不一定是单一的样式，因此，view type使得多样式的列表结构变得简单清晰。

直接贴代码，再分析。

哦，在这之前，先效果图:

代码很简单，主要就是在adapter里面重写

getViewTypeCount()

getItemViewType(int position)这两个方法。MultiStyleListAdapter.java:

<pre name="code" class="java">public class MultiStyleListAdapter extends AbstractListAdapter<Object> {        private Class[] dataClasses;@Overridepublic View getView(int position, View view, ViewGroup parent) {int viewType=getItemViewType(position);if (viewType==0) {view = getStyle1View(position, view, parent);}else if (viewType==1) {view = getStyle2View(position, view, parent);} else if(viewType==2){view = getStyle3View(position, view, parent);}else if(viewType==3){view=getStyle4View(position, view, parent);}return view;}public MultiStyleListAdapter(Context context) {// TODO Auto-generated constructor stubsuper(context);dataClasses=new Class[]{Data1.class,Data2.class,Data3.class,Data4.class};}    /**     * 注意返回的类型：     * 如果只有1种布局类型，那么返回的type是0；     * 如果2种类型，必须是0,1     * 如果3种类型，必须是0,1,2     * 。。。。     * 依次类推     * @param position 根据position返回对应位置的视图类型     * @return     */@Overridepublic int getItemViewType(int position) {// TODO Auto-generated method stubObject object=getItem(position);for(int i=0,size=dataClasses.length;i<size;i++){if(object.getClass()== dataClasses[i]){return i;}}return 0;}    /**     * @return 返回值是，布局种类总数     */@Overridepublic int getViewTypeCount() {// TODO Auto-generated method stubreturn dataClasses.length;}private View getStyle1View(final int position, View convertView,ViewGroup parent) {final Styly1ViewHolder holder;if (convertView == null) {convertView = mInflater.inflate(R.layout.item_style_1, null);holder = new Styly1ViewHolder(convertView);convertView.setTag(holder);} else {holder = (Styly1ViewHolder) convertView.getTag();}final Data1 item=(Data1)mList.get(position);holder.tvIndex.setText("index="+position);holder.content.setText(item.content);return convertView;}private View getStyle2View(final int position, View convertView,   ViewGroup parent) {final Styly2ViewHolder holder;if (convertView == null) {convertView = mInflater.inflate(R.layout.item_style_2, null);holder = new Styly2ViewHolder(convertView);convertView.setTag(holder);} else {holder = (Styly2ViewHolder) convertView.getTag();}final Data2 item=(Data2)mList.get(position);holder.tvIndex.setText("index="+position);holder.pic.setImageResource(item.img);return convertView;}private View getStyle3View(final int position, View convertView,   ViewGroup parent) {final Styly3ViewHolder holder;if (convertView == null) {convertView = mInflater.inflate(R.layout.item_style_3, null);holder = new Styly3ViewHolder(convertView);convertView.setTag(holder);} else {holder = (Styly3ViewHolder) convertView.getTag();}final Data3 item=(Data3)mList.get(position);holder.tvIndex.setText("index="+position);holder.pic1.setImageResource(item.img1);holder.pic2.setImageResource(item.img2);holder.pic3.setImageResource(item.img3);return convertView;}private View getStyle4View(final int position, View convertView,   ViewGroup parent) {final Styly4ViewHolder holder;if (convertView == null) {convertView = mInflater.inflate(R.layout.item_style_4, null);holder = new Styly4ViewHolder(convertView);convertView.setTag(holder);} else {holder = (Styly4ViewHolder) convertView.getTag();}final Data4 item=(Data4)mList.get(position);holder.tvIndex.setText("index="+position);holder.checkBox.setText(item.content);holder.checkBox.setChecked(item.isChecked);return convertView;}class Styly1ViewHolder {TextView tvIndex;TextView content;public Styly1ViewHolder(View root){content=(TextView)root.findViewById(R.id.content);tvIndex=(TextView)root.findViewById(R.id.index);}}class Styly2ViewHolder {TextView tvIndex;ImageView pic;public Styly2ViewHolder(View root){pic=(ImageView)root.findViewById(R.id.content);tvIndex=(TextView)root.findViewById(R.id.index);}}class Styly3ViewHolder {TextView tvIndex;ImageView pic1;ImageView pic2;ImageView pic3;public Styly3ViewHolder(View root){pic1=(ImageView)root.findViewById(R.id.img1);pic2=(ImageView)root.findViewById(R.id.img2);pic3=(ImageView)root.findViewById(R.id.img3);tvIndex=(TextView)root.findViewById(R.id.index);}}class Styly4ViewHolder {TextView tvIndex;CheckBox checkBox;public Styly4ViewHolder(View root){checkBox=(CheckBox)root.findViewById(R.id.checkbox);tvIndex=(TextView)root.findViewById(R.id.index);}}}

demo用了4个样式，分别对应4个viewholder，定义4个数据模型，data1,data2,data3,data4，根据viewtype来实例化或复用对应view，并绑定对应数据。

注意getViewType返回值，必须从0开始，依次增大。否则要抛ArrayIndexOutOfBoundsException异常，原因文章后面分析。

AbstractListAdapter.java 继承至BaseAdapter，只是对它进行部分重写和封装，以及使用泛型后的一个基类。

还是把贴出来吧，免得对新手造成疑惑。

public abstract class AbstractListAdapter <T> extends BaseAdapter {    protected List<T> mList;    protected Context mContext;    private AdapterView mListView;    protected LayoutInflater mInflater;    public AbstractListAdapter(Activity context) {        this.mContext = context;        mInflater = LayoutInflater.from(context);    }    public AbstractListAdapter(Context context) {    mContext=context;        mInflater = LayoutInflater.from(context);    }    @Override    public Object getItem(int i) {        return mList == null ? null : mList.get(i);    }    @Override    public int getCount() {        return mList == null ? 0 : mList.size();    }    @Override    public long getItemId(int i) {        return i;    }    @Override    public abstract View getView(int i, View view, ViewGroup viewGroup);    public void setList(List<T> list) {        this.mList = list;    }    public List<T> getList() {        return this.mList;    }    public AdapterView getListView(){        return mListView;    }    public void setListView(AdapterView listView){        mListView = listView;    }    public Context getContext(){        return mContext;    }    public void setList(T[] list){        if (list == null) return;        ArrayList<T> arrayList = new ArrayList<T>(list.length);        for (T t : list) {            arrayList.add(t);        }        setList(arrayList);    }    public void clear() {        if (mList != null && mList.size() > 0){            mList.clear();        }    }}

然后添加示例数据：

MainActivity.java

public class MainActivity extends AppCompatActivity {    private ListView mListview;    private MultiStyleListAdapter mAdapter;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mListview=(ListView)findViewById(R.id.listview);        mAdapter=new MultiStyleListAdapter(this);        mListview.setAdapter(mAdapter);        createData();    }    private void createData(){        List<Object> dataAll=new ArrayList<>();        dataAll.add(new Data1("打开链接快乐大脚"));        dataAll.add(new Data2(R.drawable.img1));        dataAll.add(new Data2(R.drawable.img2));        dataAll.add(new Data1("萨达姆分，吗，"));        dataAll.add(new Data3(R.drawable.img3,R.drawable.img4,R.drawable.img5));        dataAll.add(new Data4("昂啥呢",true));        dataAll.add(new Data3(R.drawable.img6,R.drawable.img7,R.drawable.img8));        dataAll.add(new Data1("萨达姆分，吗，"));        dataAll.add(new Data2(R.drawable.img9));        dataAll.add(new Data2(R.drawable.img10));        dataAll.add(new Data2(R.drawable.img11));        dataAll.add(new Data1("暗红色的尽快和圣诞节快放假"));        dataAll.add(new Data1("跨境开理发店了"));        dataAll.add(new Data1("1434"));        dataAll.add(new Data1("地方"));        dataAll.add(new Data1("主线程执行"));        dataAll.add(new Data4("ansdklma,sdm,",true));        dataAll.add(new Data4("撒角度看",true));        dataAll.add(new Data3(R.drawable.img12,R.drawable.img13,R.drawable.img14));        dataAll.add(new Data1("暗红色的尽快和圣诞节快放假"));        dataAll.add(new Data1("13123123"));        dataAll.add(new Data1("154667678"));        mAdapter.setList(dataAll);        mAdapter.notifyDataSetChanged();    }}

好了，代码贴完，可以开始分析了。

大家都知道listview，gridview都是继承至abslistview。它的回收能力来自于abslistview。

滚动时，超出屏幕的视图会被扔进回收站，当listview判定出即将有item进入屏幕时，又会从回收站里面把视图拿出来重用，当然，前提是回收站里有满足要求的视图。否则会创建新实例。这部分源码不是重点，有兴趣的同学自行查看源码或相关文档。

RecycleBin，这就是这个回收站，在listview实例创建时而被创建。其中有几个比较重要的成员变量

View[] mActiveViews 存的是处于屏幕里的view

ArrayList<View>[] mScrapViews; 存的是所有废弃的view，它就是我们要说的重点。这个数组的每个元素都是一个view的集合，其实也就是每个类型一个集合。RecycleBin.setViewTypeCount(int viewTypeCount)是在listview的setAdapter里面被调用的，这时就会根据type的数量创建对应个数的view集合。getScrapView()里以viewType取集合，所以，前面所说的adapter里面的getviewtype的返回值必须从0开始，且不间断的自然数。

class RecycleBin {      //根据viewtype的种类数量创建arraylist的数组public void setViewTypeCount(int viewTypeCount) {    if (viewTypeCount < 1) {        throw new IllegalArgumentException("Can't have a viewTypeCount < 1");    }    //noinspection unchecked    ArrayList<View>[] scrapViews = new ArrayList[viewTypeCount];    for (int i = 0; i < viewTypeCount; i++) {        scrapViews[i] = new ArrayList<View>();    }    mViewTypeCount = viewTypeCount;    mCurrentScrap = scrapViews[0];    mScrapViews = scrapViews;}//从垃圾堆里重新取得viewprivate View retrieveFromScrap(ArrayList<View> scrapViews, int position) {    final int size = scrapViews.size();    if (size > 0) {        // See if we still have a view for this position or ID.        for (int i = 0; i < size; i++) {            final View view = scrapViews.get(i);            final AbsListView.LayoutParams params =                    (AbsListView.LayoutParams) view.getLayoutParams();            if (mAdapterHasStableIds) {                final long id = mAdapter.getItemId(position);                if (id == params.itemId) {                    return scrapViews.remove(i);                }            } else if (params.scrappedFromPosition == position) {                final View scrap = scrapViews.remove(i);                clearAccessibilityFromScrap(scrap);                return scrap;            }        }        final View scrap = scrapViews.remove(size - 1);        clearAccessibilityFromScrap(scrap);        return scrap;    } else {        return null;    }}//根据viewtype获取对应类型的view集合View getScrapView(int position) {    final int whichScrap = mAdapter.getItemViewType(position);    if (whichScrap < 0) {        return null;    }    if (mViewTypeCount == 1) {        return retrieveFromScrap(mCurrentScrap, position);    } else if (whichScrap < mScrapViews.length) {        //以viewtype为下标取集合        return retrieveFromScrap(mScrapViews[whichScrap], position);    }    return null;}}

listview里的每个视图就是在这个方法中被创建的absListView.obtainView(int position, boolean[] isScrap){......//从回收站重新取出对应type的viewfinal View scrapView = mRecycler.getScrapView(position);//再传入getview里重新绑定数据。final View child = mAdapter.getView(position, scrapView, this);......}

absListView的obtainview方法创建或者复用回收站里面的viewabsListView的trackMotionScroll--->mRecycler.addScrapView(child, position);trackMotionScroll滚动时会被调用，这里面判断哪些view被废弃。所以listview滚动时，判定哪些view超出屏幕，超出就被放入回收站里，等又需要view的时候，listview根据viewtype类型从回收站里取出来复用，并回调到adapter的getview方法里面，从而达到多类型复用的效果demo源码：https://github.com/qinzhen308/ListviewExploreDemo或http://download.csdn.net/detail/qinzhen308/9603718

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