用PopupWindow实现下拉列表，并再次熟悉一些其他基础知识点。

本文仅供菜鸟交流观看，大神请绕路。

这里首先要明确一下需求，并不单单是为了用一个PopupWindow来实现一个下拉列表

需求1：PopupWindow实现下来列表

需求2：点击选中列表中item中时，item中显示字体，再次点击字体隐藏。

需求3：所有选中的item，不论是什么顺序选择的，最后都按position（用的listview）的大小，从小到大排列然后显示在textview里。

其实需求写明白后，就知道如何去实现这些功能了。 话不多说 贴出代码.

public class MainActivity extends AppCompatActivity implements View.OnClickListener {    private TextView textView;    private ListView listView;    private PopupWindow popupWindow;    private MyAdapter myAdapter;    private List<BeanVo> data;    //    private List<String> textList = new ArrayList<String>();    private Map<Integer, String> map = new HashMap<Integer, String>();    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initUI();    }    private void initUI() {        textView = (TextView) findViewById(R.id.tv);        textView.setOnClickListener(this);    }    private void initSeletPopup() {        listView = new ListView(this);        testData();        myAdapter = new MyAdapter(this, data);        listView.setAdapter(myAdapter);        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {            @Override            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {                BeanVo beanVo = data.get(position);                if (beanVo.isShow()) {                    map.remove(position);                    beanVo.setShow(false);                } else {                    map.put(position, data.get(position).getName());                    beanVo.setShow(true);                }                myAdapter.notifyDataSetChanged();            }        });        popupWindow = new PopupWindow(listView, textView.getWidth(), ActionBar.LayoutParams.WRAP_CONTENT, true);        Drawable drawable = ContextCompat.getDrawable(this, R.drawable.bg_corner);        popupWindow.setBackgroundDrawable(drawable);        popupWindow.setFocusable(true);        popupWindow.setOutsideTouchable(true);        popupWindow.setOnDismissListener(new PopupWindow.OnDismissListener() {            @Override            public void onDismiss() {                if (map.size() > 0) {                    String tmp = "";                    int[] ints = sortPosition();                    for (int i = 0; i < map.size(); i++) {                        tmp = tmp + map.get(ints[i]);                    }                    textView.setText(tmp);                }                popupWindow.dismiss();            }        });    }    @Override    public void onClick(View view) {        switch (view.getId()) {            case R.id.tv:                map.clear();                initSeletPopup();                if (popupWindow != null && !popupWindow.isShowing()) {                    popupWindow.showAsDropDown(textView, 0, 10);                }                break;        }    }    private void testData() {        data = new ArrayList<>();        for (int i = 0; i < 20; i++) {            BeanVo beanVo = new BeanVo();            beanVo.setName("数据" + i);            beanVo.setShow(false);            data.add(beanVo);        }    }    private int[] sortPosition() {        Set<Integer> str = map.keySet();        Object[] tt = str.toArray();        int N = map.size();        int[] arr = new int[N];        int a = 0;        for (Object oo : tt) {            if (oo instanceof Integer) {                arr[a] = (Integer) oo;            }            a++;        }
       for (int i = arr.length - 1; i > 0; i--) {            for (int j = 1; j <= i; j++) {                if (arr[j - 1] > arr[j]) {                    int tmp = arr[j - 1];                    arr[j - 1] = arr[j];                    arr[j] = tmp;                }            }        }        return arr;    }
}


public class MyAdapter extends BaseAdapter {    private List<BeanVo> mData;    private LayoutInflater layoutInflater;    private Context mContext;    HashMap<Integer, View> hashMap = new HashMap<Integer, View>();    public MyAdapter(Context context, List data) {        this.mContext = context;        this.mData = data;        this.layoutInflater = LayoutInflater.from(context);    }    @Override    public int getCount() {        return mData.size();    }    @Override    public Object getItem(int position) {        return mData.get(position);    }    @Override    public long getItemId(int position) {        return position;    }    @Override    public View getView(int position, View convertView, ViewGroup viewGroup) {        ViewHolder viewHolder = null;//        if (hashMap.get(position)==null) {//如果变化的对象没有绑定position，该方法可以防止复用        if (convertView == null) {            viewHolder = new ViewHolder();            convertView = layoutInflater.inflate(R.layout.popup_text_item, null);            viewHolder.tv_data = convertView.findViewById(R.id.tv_data);            viewHolder.select_tv = convertView.findViewById(R.id.select_tv);            convertView.setTag(viewHolder);//            hashMap.put(position,convertView);        } else {//            convertView=hashMap.get(position);            viewHolder = (ViewHolder) convertView.getTag();        }        viewHolder.tv_data.setText(mData.get(position).getName());        if (mData.get(position).isShow()) {            viewHolder.select_tv.setVisibility(View.VISIBLE);        } else {            viewHolder.select_tv.setVisibility(View.GONE);        }        return convertView;    }    public class ViewHolder {        public TextView tv_data;        public TextView select_tv;    }}

public class BeanVo {    public String name;    public boolean show;    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public boolean isShow() {        return show;    }    public void setShow(boolean show) {        this.show = show;    }}


由于代码比较简单，里面就没有什么备注了，一看就懂了。