android - java.lang.NullPointerException，我不知道为什么

Question

package com.nicotera.colton.londontransitguide;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.Spinner;

public class RoutesActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

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

        // Create an ArrayAdapter using the string array and a default 
        // spinner layout
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
            this, R.array.routes_array, android.R.layout.simple_spinner_item
        );

        // Specify the layout to use when the list of choices appears
        adapter.setDropDownViewResource(
            android.R.layout.simple_spinner_dropdown_item
        );

        // Apply the adapter to the spinner
        spinner.setAdapter(adapter);

        // TODO Auto-generated method stub
    }
}

结果:

12-06 23:34:28.954: E/AndroidRuntime(765): Caused by: java.lang.NullPointerException
12-06 23:34:28.954: E/AndroidRuntime(765): at com.nicotera.colton.londontransitguide.RoutesActivity.onCreate(RoutesActivity.java:22)

看来问题出在第 22 行，但我无法弄清楚到底出了什么问题？我是一名全新的开发人员，非常感谢您提供的所有帮助!

Answer 1

我猜第 22 行是:

spinner.setAdapter(adapter);

这意味着微调器为空。因此，调用 findViewById() 返回 null。检查您的布局，是否有 ID 为“R.id.route_name_spinner”的微调器？