Android开发：仿美团下拉列表菜单，帮助类，复用简单

public class MenuHelper {
	private PopupWindow popupWindow;
	private ListView listView;
	private List<String> data;
	private Context mContext;
	private View topView;
	private ListAdapter adapter;
	private int i = 0;
	private FrameLayout container;

	public MenuHelper(Context context, View topView, final OnMenuClick clickListener, List<String> data, FrameLayout containerView) {
		mContext = context;
		this.topView = topView;
		this.data = data;
		
		this.container = containerView;
		container.getForeground().setAlpha(0);
		
		initListView(clickListener);
		initPopupWindow();
		
	}
	
	private void initListView(final OnMenuClick clickListener) {
		listView = new ListView(mContext);
		listView.setDivider(null);
		listView.setDividerHeight(0);
		listView.setBackgroundColor(Color.WHITE);
		adapter = new ListAdapter(mContext);
		listView.setAdapter(adapter);
		
		listView.setOnItemClickListener(new OnItemClickListener() {
			@Override
			public void onItemClick(AdapterView<?> parent, View view,
					int position, long id) {
				i = position;
				clickListener.onPopupMenuClick(position);
				popupWindow.dismiss();
			}
		});
	}
	
	private void initPopupWindow() {
		popupWindow = new PopupWindow(listView, LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT, true);
		popupWindow.setOutsideTouchable(true);
		popupWindow.setBackgroundDrawable(new ColorDrawable(Color.WHITE));
		
		popupWindow.setOnDismissListener(new OnDismissListener() {
			@Override
			public void onDismiss() {
				if (container != null) {
					container.getForeground().setAlpha(0);
				}
			}
		});
	}
	
	public void showMenu() {
		adapter.notifyDataSetChanged();
		if (popupWindow.isShowing()) {
			popupWindow.dismiss();
		}else {
			popupWindow.setOutsideTouchable(true);
			popupWindow.setTouchable(true);
			popupWindow.showAsDropDown(topView, 0, 0);
			if (container != null) {
				container.getForeground().setAlpha(120);
			}
		}
	}

	private class ListAdapter extends ArrayAdapter<String> {

		public ListAdapter(Context context) {
			super(context, R.layout.item_text, data);
		}
		
		private Holder getHolder(final View view) {
	        Holder holder = (Holder) view.getTag();
	        if (holder == null) {
	            holder = new Holder(view);
	            view.setTag(holder);
	        }
	        return holder;
	    }
		
		@Override
		public View getView(final int position, View convertView, ViewGroup parent) {
			View rowView = convertView;
			if (rowView == null) {
				LayoutInflater inflater = LayoutInflater.from(mContext);
				rowView = inflater.inflate(R.layout.item_text, null);
			}
			final Holder holder = getHolder(rowView);
			
			holder.textview.setText(data.get(position));
			if (position == i) {
				holder.textview.setBackgroundColor(mContext.getResources().getColor(R.color.item_press));
			}else {
				holder.textview.setBackgroundColor(Color.TRANSPARENT);
			}
			
			return rowView;
		}

		private class Holder {
			public TextView textview;
			
			public Holder(View view) {
				textview = (TextView) view.findViewById(R.id.textView);
			}
		}  
	}
}

public interface OnMenuClick {
	public void onPopupMenuClick(int position);
}

public class MainActivity extends Activity implements OnMenuClick{
	private MenuHelper mMenuHelper;
	private Button button;
	private FrameLayout container;
	private List<String> menuData;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		container = (FrameLayout) findViewById(R.id.container);
		button = (Button) findViewById(R.id.button);
		
		menuData = new ArrayList<String>();
		menuData.add("ladfj");
		menuData.add("ladfj");
		menuData.add("ladfj");
		menuData.add("ladfj");
		menuData.add("ladfj");
		
		mMenuHelper = new MenuHelper(this, button, this, menuData, container);
		
		button.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				mMenuHelper.showMenu();
			}
		});
		
	}

	@Override
	public void onPopupMenuClick(int position) {
		Log.d("debug", "click position " + position);
	}
	
}