Spinner OnItemSelectedListener不起作用

Question

我正在创建一个Android应用程序...我有两个Spinner下拉列表。似乎我无法使OnItemSelectedListener正常工作。当一个项目被选中时我没有错误，它只返回null ..我花了一整天的时间试图找出我做错了什么......没有运气。

下面是相关代码。如果您需要更多代码，请告诉我

  //grab the user defined make and model for the listing search
    spin_make = (Spinner) findViewById(R.id.spinr_make);
    spin_model = (Spinner) findViewById(R.id.spinr_model);

    //load the drop downs
    ArrayAdapter<String> makeAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, make_list);
    spin_make.setAdapter(makeAdapter);    

    //set the item selected listener for the make drop down
    spin_make.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            model_list.clear();
            new LoadModelListsTask().execute();
            ArrayAdapter<String> modelAdapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_spinner_dropdown_item, model_list);
            spin_model.setAdapter(modelAdapter);
            _make = make_list.get(position);
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {

        }
    });