java - spinner.setAdapter() 中的 NullPointerException

Question

我想创建一个微调器来显示列表m。但以下代码在 spinner.setAdapter(spinner_adapter) 处给出了 NullPointerException。为什么会出现这种情况？

public class Request extends ListActivity {
    private static final String[] m={"A","B","O","AB","others"};   
    private TextView view;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        SimpleAdapter adapter = new SimpleAdapter(this, getData(),
            R.layout.listitem, new String[] { "name", "quant" },
            new int[] {R.id.name, R.id.quant });
        setListAdapter(adapter);

        view = (TextView) findViewById(R.id.spinnerText);  
        Spinner spinner = (Spinner) findViewById(R.id.spinner01);  
        ArrayAdapter<String> spinner_adapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item,m);  
        spinner_adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);  
        spinner.setAdapter(spinner_adapter);              
        spinner.setOnItemSelectedListener(new SpinnerSelectedListener());  
        spinner.setVisibility(View.VISIBLE);  
    }

    class SpinnerSelectedListener implements OnItemSelectedListener{              
        public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,  
            long arg3) {  
            view.setText(""+m[arg2]);  
        }  
        public void onNothingSelected(AdapterView<?> arg0) {       
        }  
    }
}

Answer 1

你的线路

    Spinner spinner = (Spinner) findViewById(R.id.spinner01);

最终 spinner 为空，因为没有内容 View 分配给您的 Activity 。

因此，当尝试与微调器交互时，会抛出 NPE。

在初始化其 View 之前，将 setContentView(R.layout.your_layout_content); 添加到 onCreate 方法。