spinner中的onNothingSelected方法到底什么时候调用？

这个东东大家在开发中可能不太能用到，所以总是容易被忽略，由于工作原因，我最近琢磨了一下onNothingSelected方法的调用时机问题，其实很简单，只要我们稍微看一下源码就明白了：

        /**
         * Callback method to be invoked when the selection disappears from this
         * view. The selection can disappear for instance when touch is activated
         * or when the adapter becomes empty.
         *
         * @param parent The AdapterView that now contains no selected item.
         */
        void onNothingSelected(AdapterView<?> parent);

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		initData();
		provinces = (Spinner) this.findViewById(R.id.provinces);
		adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item,
				data);
		provinces.setAdapter(adapter);
		provinces.setOnItemSelectedListener(new OnItemSelectedListener() {

			@Override
			public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
				Log.d("qianfeng", "您选择了" + data.get(position));
			}

			@Override
			public void onNothingSelected(AdapterView<?> parent) {
				Log.d("qianfeng", "NothingSelected");
			}
		});
	}
	
	/**
	 * 点击button时，将集合中的数据全部移除，同时调用adapter的notifyDataSetChanged方法
	 * @param view
	 */
	public void btnClick(View view){
		data.removeAll(data);
		adapter.notifyDataSetChanged();
	}

	private void initData() {
		data = new ArrayList<String>();
		data.add("山东");
		data.add("广西");
		data.add("陕西");
		data.add("广东");
	}

spinner中的onNothingSelected方法到底什么时候调用？

原文：http://blog.csdn.net/u012702547/article/details/50598673