.setAdapter（适配器）；给出 NullPointerException答案

【问题标题】：.setAdapter(adapter); Giving an NullPointerException.setAdapter（适配器）；给出 NullPointerException
【发布时间】：2012-07-05 22:27:16
【问题描述】：

我正在尝试为微调器制作适配器，但是我在 answertime.setAdapter(adapter); 上收到 NullPointerException为什么是这样？我的数组在它们应该在的 strings.xml 中？这是完整的代码。

package lijap.app.starcraft2counters;

import java.io.File;

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;

public class Settings extends Activity implements OnItemSelectedListener {
Spinner answertime;
Spinner gametime;
Spinner missesallowed;

String[] answerseconds = { "Unlimited", "1 second", "2 seconds",
        "3 seconds", "4 seconds", "5 seconds" };

String[] gameminutes = { "Unlimited", "1 minute", "2 minutes", "3 minutes",
        "4 minutes", "5 minutes" };

String[] numberofmisses = { "Unlimited", "5", "10", "15", "20", "25" };

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.settings);

    ArrayAdapter adapter = ArrayAdapter.createFromResource(this, R.array.AnswerSeconds, R.layout.custom_spinner_list);
    adapter.setDropDownViewResource(R.layout.custom_spinner);
    answertime.setAdapter(adapter);

    ArrayAdapter adapter2 = ArrayAdapter.createFromResource(this, R.array.GameMinutes, R.layout.custom_spinner_list);
    adapter.setDropDownViewResource(R.layout.custom_spinner);
    gametime.setAdapter(adapter);

    ArrayAdapter adapter3 = ArrayAdapter.createFromResource(this, R.array.NumberOfMisses, R.layout.custom_spinner_list);
    adapter.setDropDownViewResource(R.layout.custom_spinner);
    missesallowed.setAdapter(adapter);


    answertime = (Spinner) findViewById(R.id.s_answertime);
    answertime.setAdapter(adapter);
    answertime.setOnItemSelectedListener(this);


    missesallowed = (Spinner) findViewById(R.id.s_mistakenumber);
    missesallowed.setAdapter(adapter2);
    missesallowed.setOnItemSelectedListener(this);

    gametime = (Spinner) findViewById(R.id.s_gametime);
    gametime.setAdapter(adapter3);
    gametime.setOnItemSelectedListener(this);
}

@Override
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
        long arg3) {
    // TODO Auto-generated method stub

}

@Override
public void onNothingSelected(AdapterView<?> arg0) {
    // TODO Auto-generated method stub

}

}

感谢任何帮助 - Lijap

【问题讨论】：

标签： android arrays android-arrayadapter

【解决方案1】：

你需要初始化

Spinner answertime;
Spinner gametime;
Spinner missesallowed;

否则，以下行会给你一个NullPointerException：

answertime.setAdapter(adapter);
gametime.setAdapter(adapter);
missesallowed.setAdapter(adapter);

要初始化Spinners，您应该在调用setContentView后添加类似这样的内容：

answertime = findViewById(R.id.answertime);
gametime = findViewById(R.id.gametime);
missesallowed = findViewById(R.id.missesallowed);

【讨论】：

【解决方案2】：

您永远不会初始化 answertime、gametime 或 missesallowed。你需要做这样的事情，

answertime = findViewById(R.id.<the id for this spinner>);
gametime = findViewById(R.id.<the id for this spinner>);
missesallowed = findViewById(R.id.<the id for this spinner>);

在您致电setAdapter() 之前。

还有一个问题，

ArrayAdapter adapter2 = ArrayAdapter.createFromResource(this, R.array.GameMinutes, R.layout.custom_spinner_list);
adapter.setDropDownViewResource(R.layout.custom_spinner);
gametime.setAdapter(adapter);

请注意，您在引用adapter2 中构造了一些内容，然后修改adapter，并将adapter 设置为微调器的适配器。这就是你想要的吗？

【讨论】：

【解决方案3】：

还要确保视图可见性设置为 View.VISIBLE

【讨论】：