片段内的微调器答案

【问题标题】：A Spinner inside a Fragment片段内的微调器
【发布时间】：2018-09-08 17:55:55
【问题描述】：

我正在创建一个简单的 android 游戏应用程序，但我在我的片段内的微调器中遇到了一些问题。我尝试了一些解决方案，但我的应用程序仍然崩溃。有人能帮我吗？万分感谢。

 public class SlotMachineFragmentOne extends Fragment {

 Spinner dropdown;

 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.activity_slotmachine_fragment_one, container, false);

    initspinnerfooter();
    dropdown = rootView.findViewById(R.id.spinner);

    return rootView;
}

private void initspinnerfooter() {
    String[] items = new String[]{
            "Choose apple", "Choose boy", " Choose cat", "Choose dog", 
    };

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_spinner_item, items);
    dropdown.setAdapter(adapter);
    dropdown.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            Log.v("item", (String) parent.getItemAtPosition(position));
            ((TextView) parent.getChildAt(0)).setTextColor(Color.WHITE);
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {
            // TODO Auto-generated method stub
        }
    });
}   }

【问题讨论】：

标签： android android-fragments spinner

【解决方案1】：

在dropdown = rootView.findViewById(R.id.spinner);之后调用initspinnerfooter();

像这样：

    @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.activity_slotmachine_fragment_one, container, false);

    dropdown = rootView.findViewById(R.id.spinner);
    initspinnerfooter();

    return rootView;
}

【讨论】：

【解决方案2】：

你在初始化之前访问dropdown对象，这就是它抛出NullPointerException的原因

先初始化再使用

公共类 SlotMachineFragmentOne 扩展片段 {

 Spinner dropdown;

 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.activity_slotmachine_fragment_one, container, false);


    dropdown = rootView.findViewById(R.id.spinner);
    initspinnerfooter();

    return rootView;
}

private void initspinnerfooter() {
    String[] items = new String[]{
            "Choose apple", "Choose boy", " Choose cat", "Choose dog", 
    };

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_spinner_item, items);
    dropdown.setAdapter(adapter);
    dropdown.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            Log.v("item", (String) parent.getItemAtPosition(position));
            ((TextView) parent.getChildAt(0)).setTextColor(Color.WHITE);
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {
            // TODO Auto-generated method stub
        }
    });
}   }

【讨论】：

感谢您解释我的问题的答案。 +1