Android自定义适配器显示错误

我正在尝试创建自定义适配器listview

但是当我尝试启动应用程序时，应用程序崩溃并显示以下错误

我的main活动看起来像

package com.app.test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import android.R.string;
import android.os.Bundle;
import android.app.Activity;
import android.app.ListActivity;
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {


    private ArrayList<Custom> fetch = new ArrayList<Custom>();
    private ListView lv;
    private CustomAdapter adapter;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main);

        Custom one = new Custom("Big1","Small1");
        fetch.add(one);

        lv = (ListView) findViewById(R.id.listview);
        adapter = new CustomAdapter(MainActivity.this,
                R.id.listview,
                fetch);
        lv.setAdapter(adapter);


    }

}

CustomAdapter.java

package com.app.test;

public class Custom {
private String customBig;
private String customSmall;

public Custom(String string, String string2) {
this.customBig = string;
this.customSmall = string2;
}
public String getcustomBig() { return customBig; }
public void setcustomBig(String customBig) { this.customBig = customBig; }

public String getcustomSmall() { return customSmall; }
public void setcustomSmall(String customSmall) { this.customSmall = customSmall; }
}

package com.app.test;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

public class CustomAdapter extends ArrayAdapter<Custom>{
    private ArrayList<Custom> entries;
    private Activity activity;

    public CustomAdapter(Activity a, int textViewResourceId, ArrayList<Custom> entries) {
        super(a, textViewResourceId, entries);
        this.entries = entries;
        this.activity = a;
    }

    public static class ViewHolder{
        public TextView item1;

    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View v = convertView;
        ViewHolder holder;
        if (v == null) {
            LayoutInflater vi =
                (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.temp, null);
            holder = new ViewHolder();
            holder.item1 = (TextView) v.findViewById(R.id.name);
            v.setTag(holder);
        }
        else
            holder=(ViewHolder)v.getTag();

        final Custom custom = entries.get(position);
        if (custom != null) {
            holder.item1.setText(custom.getcustomSmall());

        }
        return v;
    }

}

你必须取消注释

//setContentView(R.layout.activity_main);

---

否则Android无法为

活动创建
视图
层次结构

为什么您评论了

设置内容视图（R.layout.Activity\u main）活动中的行？嗨，还有一个疑问。如何通过循环向自定义添加值？当我尝试时，只显示最后一个值。你能帮忙吗？
package com.app.test;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

public class CustomAdapter extends ArrayAdapter<Custom>{
    private ArrayList<Custom> entries;
    private Activity activity;

    public CustomAdapter(Activity a, int textViewResourceId, ArrayList<Custom> entries) {
        super(a, textViewResourceId, entries);
        this.entries = entries;
        this.activity = a;
    }

    public static class ViewHolder{
        public TextView item1;

    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View v = convertView;
        ViewHolder holder;
        if (v == null) {
            LayoutInflater vi =
                (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.temp, null);
            holder = new ViewHolder();
            holder.item1 = (TextView) v.findViewById(R.id.name);
            v.setTag(holder);
        }
        else
            holder=(ViewHolder)v.getTag();

        final Custom custom = entries.get(position);
        if (custom != null) {
            holder.item1.setText(custom.getcustomSmall());

        }
        return v;
    }

}

01-08 16:23:10.878: E/AndroidRuntime(2704): FATAL EXCEPTION: main
01-08 16:23:10.878: E/AndroidRuntime(2704): Process: com.app.test, PID: 2704
01-08 16:23:10.878: E/AndroidRuntime(2704): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.app.test/com.app.test.MainActivity}: java.lang.NullPointerException
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.os.Looper.loop(Looper.java:136)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.app.ActivityThread.main(ActivityThread.java:5017)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at java.lang.reflect.Method.invokeNative(Native Method)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at java.lang.reflect.Method.invoke(Method.java:515)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at dalvik.system.NativeStart.main(Native Method)
01-08 16:23:10.878: E/AndroidRuntime(2704): Caused by: java.lang.NullPointerException
01-08 16:23:10.878: E/AndroidRuntime(2704):     at com.app.test.MainActivity.onCreate(MainActivity.java:43)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.app.Activity.performCreate(Activity.java:5231)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-08 16:23:10.878: E/AndroidRuntime(2704):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
01-08 16:23:10.878: E/AndroidRuntime(2704):     ... 11 more

//setContentView(R.layout.activity_main);