Android - Java NullPointerException

Question

我正在尝试制作一个简单的应用程序,但我遇到了这个令人讨厌的错误,我无法找出原因......

01-06 18:05:04.734: E/AndroidRuntime(1102): FATAL EXCEPTION: main
01-06 18:05:04.734: E/AndroidRuntime(1102): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.coindroid/com.example.coindroid.EUActivity}: java.lang.NullPointerException
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.os.Looper.loop(Looper.java:137)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.app.ActivityThread.main(ActivityThread.java:5041)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at java.lang.reflect.Method.invokeNative(Native Method)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at java.lang.reflect.Method.invoke(Method.java:511)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at dalvik.system.NativeStart.main(Native Method)
01-06 18:05:04.734: E/AndroidRuntime(1102): Caused by: java.lang.NullPointerException
01-06 18:05:04.734: E/AndroidRuntime(1102):     at com.example.coindroid.EUActivity.onCreate(EUActivity.java:30)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.app.Activity.performCreate(Activity.java:5104)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
01-06 18:05:04.734: E/AndroidRuntime(1102):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
01-06 18:05:04.734: E/AndroidRuntime(1102):     ... 11 more

所以,似乎我的问题在第30行,即:list.setAdapter(new EUAdapter(this)); 怎么了 ？我的活动是这样的:

    package com.example.coindroid;

    import java.util.ArrayList;
import android.app.Activity; 
import android.content.Context; 
import android.content.res.Resources; 
import android.os.Bundle; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.BaseAdapter; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.TextView;

    public class EUActivity extends Activity {      

ListView list;

        @Override   protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);         
setContentView(R.layout.activity_eu);       
list = (ListView) findViewById(R.layout.activity_eu);

                    list.setAdapter(new EUAdapter(this));        
}

        }

             class SingleRow {  String title;   String description;     int image;  SingleRow(String title, String description, int image)  {       this.title = title;         this.description = description;         this.image = image;     } } class EUAdapter extends BaseAdapter{

        ArrayList<SingleRow> list;  Context context;    EUAdapter(Context c)    {       context = c;        list = new ArrayList<SingleRow>();      Resources res = c.getResources();       String[] titles = res.getStringArray(R.array.titles);       String[] descriptions = res.getStringArray(R.array.description);        int[] images = {R.drawable.queenvictoria1841jpg};
                    for(int i=0;i<1;i++)        {           list.add(new SingleRow(titles[i], descriptions[i], images[i]));         }
                }
                @Override   public int getCount() {
                    return list.size();     }

        @Override   public Object getItem(int i) {
                    return list.get(i);     }

        @Override   public long getItemId(int i) {
                    return i;   }

        @Override   public View getView(int i, View view, ViewGroup viewGroup) {


                    LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);       View row
    = inflater.inflate(R.layout.single_row, viewGroup, false);
                    TextView title = (TextView)row.findViewById(R.id.name);         TextView description = (TextView)row.findViewById(R.id.year);       ImageView image = (ImageView)row.findViewById(R.id.imageView1);
                    SingleRow temp = list.get(i);
                    title.setText(temp.title);      description.setText(temp.description);      image.setImageResource(temp.image);
                    return row;     }   
             }

提前谢谢你们!

Answer 1

list = (ListView) findViewById(R.layout.activity_eu);

你list是空的.你找不到任何有R.layoutid的东西.使用R.id与activity_eu布局中的列表视图对应的ID .