onItemSelectedListener不会被触发

Question

我在我的微调器中调用了onItemSelectedListener，但是onItemSelected中的代码没有被执行。

下面是我的代码：

final MaterialBetterSpinner materialDesignSpinner = (MaterialBetterSpinner)
                findViewById(R.id.states_list);

ArrayAdapter<String> stateArrayAdapter = new ArrayAdapter<>(this,
                android.R.layout.simple_dropdown_item_1line, getResources().getStringArray(R.array.oman_states));

materialDesignSpinner.setAdapter(stateArrayAdapter);


materialDesignSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                System.out.println("works");
            }

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

            }
        });

不执行System.out.println()

我在这里做错了什么？