java.lang空点异常

上面说第71行有错误，但我能猜出是什么错误，有什么灵魂愿意帮助我？谢谢

我的问题是，当我单击Main活动上的foodbutton时，系统崩溃。但是logcat在另一个页面food.java中显示了错误

这是代码

package com.yiqiexample.cabincrew;


import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
//import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;



public class Food extends ListActivity 
    implements OnClickListener {
    // Progress Dialog
        private ProgressDialog pDialog;

    //testing on Emulator:
     private static final String READ_COMMENTS_URL = "http://10.0.2.2/pbda2/foodordered.php";
    // private CheckBox chkFood, chkDrinks, chkServices;
      //private Button btnDisplay, chkClear, deliever, chkClearFood, fooddeliever, drinksdeliever, servicesdeliever, chkClearDrinks, chkClearServices;
      //private TextView clearThis,orderdisplay, clearThisFood, foodorderdisplay, drinksorderdisplay, servicesorderdisplay, clearThisDrinks, clearThisServices;

      private static final String TAG_SUCCESS = "success";
      private static final String TAG_POSTS = "posts";
        private static final String TAG_SEATNUMBER = "seatnumber";
        private static final String TAG_FOODORDERED = "foodordered";
        //it's important to note that the message is both in the parent branch of 
        //our JSON tree that displays a "Post Available" or a "No Post Available" message,
        //and there is also a message for each individual post, listed under the "posts"
        //category, that displays what the user typed as their message.

      //An array of all of our comments
        private JSONArray mComments = null;
        //manages all of our comments in a list.
        private ArrayList<HashMap<String, String>> mCommentList;



    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.setContentView(R.layout.food);



        View v = findViewById(R.id.backmain);
        //set event listener
            v.setOnClickListener(this);

            View z = findViewById(R.id.drinksbtn);
            //set event listener
                z.setOnClickListener(this);

                View x = findViewById(R.id.servicebtn);
                //set event listener
                    x.setOnClickListener(this);
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        //loading the comments via AsyncTask
        new LoadComments().execute();
    }


    /**
     * Retrieves recent post data from the server.
     */
    public void updateJSONdata() {

        // Instantiate the arraylist to contain all the JSON data.
        // we are going to use a bunch of key-value pairs, referring
        // to the json element name, and the content, for example,
        // message it the tag, and "I'm awesome" as the content..

        mCommentList = new ArrayList<HashMap<String, String>>();

        // Bro, it's time to power up the J parser 
        JSONParser jParser = new JSONParser();
        // Feed the beast our comments url, and it spits us
        //back a JSON object.  Boo-yeah Jerome.
        JSONObject json = jParser.getJSONFromUrl(READ_COMMENTS_URL);

        //when parsing JSON stuff, we should probably
        //try to catch any exceptions:
        try {

            //I know I said we would check if "Posts were Avail." (success==1)
            //before we tried to read the individual posts, but I lied...
            //mComments will tell us how many "posts" or comments are
            //available
            mComments = json.getJSONArray(TAG_POSTS);

            // looping through all posts according to the json object returned
            for (int i = 0; i < mComments.length(); i++) {
                JSONObject c = mComments.getJSONObject(i);

                //gets the content of each tag
                String seatnumber = c.getString(TAG_SEATNUMBER);
                String foodordered = c.getString(TAG_FOODORDERED);



                // creating new HashMap
                HashMap<String, String> map = new HashMap<String, String>();

                map.put(TAG_SEATNUMBER, seatnumber);
                map.put(TAG_FOODORDERED, foodordered);


                // adding HashList to ArrayList
                mCommentList.add(map);

                //annndddd, our JSON data is up to date same with our array list
            }

        } catch (JSONException e) {
            e.printStackTrace();
        }
    }









    @Override
            public void onClick(View arg0) {
        if(arg0.getId() == R.id.backmain){
            //define a new Intent for the second Activity
            Intent intent = new Intent(this,MainActivity.class);

            //start the second Activity
            this.startActivity(intent);
            }
        if(arg0.getId() == R.id.drinksbtn){
            //define a new Intent for the second Activity
            Intent intent = new Intent(this,Drinks.class);

            //start the second Activity
            this.startActivity(intent);
            }
        if(arg0.getId() == R.id.servicebtn){
            //define a new Intent for the second Activity
            Intent intent = new Intent(this,Services.class);

            //start the second Activity
            this.startActivity(intent);
            }



    }

    /**
     * Inserts the parsed data into the listview.
     */
    private void updateList() {
        // For a ListActivity we need to set the List Adapter, and in order to do
        //that, we need to create a ListAdapter.  This SimpleAdapter,
        //will utilize our updated Hashmapped ArrayList, 
        //use our single_post xml template for each item in our list,
        //and place the appropriate info from the list to the
        //correct GUI id.  Order is important here.

        ListAdapter adapter = new SimpleAdapter(this, mCommentList,
                R.layout.single_post, new String[] { TAG_SEATNUMBER, TAG_FOODORDERED
                //TAG_DRINKSORDERED, TAG_SERVICES
                         }, new int[] { R.id.seatnumber, R.id.orders
                //R.id.drinkstv, R.id.servicestv,


         });



        // I shouldn't have to comment on this one:
        setListAdapter(adapter);

        // Optional: when the user clicks a list item we 
        //could do something.  However, we will choose
        //to do nothing...
        ListView lv = getListView();    
        lv.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {

                // This method is triggered if an item is click within our
                // list. For our example we won't be using this, but
                // it is useful to know in real life applications.

            }
        });
    }   




    public class LoadComments extends AsyncTask<Void, Void, Boolean> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(Food.this);
            pDialog.setMessage("Loading orders...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }
        @Override
        protected Boolean doInBackground(Void... arg0) {
            //we will develop this method in version 2
            updateJSONdata();
            return null;

        }


        @Override
        protected void onPostExecute(Boolean result) {
            super.onPostExecute(result);
            pDialog.dismiss();
          //we will develop this method in version 2
            updateList();
        }
    }


}

food.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android1="http://schemas.android.com/apk/res/android"
    android1:id="@+id/bg2"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android1:background="#E0FFFF" >

    <Button
        android1:id="@+id/backmain"
        android1:layout_width="wrap_content"
        android1:layout_height="wrap_content"
        android1:layout_alignParentBottom="true"
        android1:layout_alignParentRight="true"
        android1:text="@string/backtomain" />

    <Button
        android1:id="@+id/servicesdelivered"
        android1:layout_width="wrap_content"
        android1:layout_height="wrap_content"
        android1:layout_above="@+id/foodbtn"
        android1:layout_alignLeft="@+id/backmain"
        android1:text="@string/servicesdelivered"
        android1:visibility="invisible" />
    <Button
        android:id="@+id/servicebtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_marginLeft="358dp"
        android:layout_toRightOf="@+id/foodbutton"
        android:text="SERVICES" />

    <Button
        android1:id="@+id/foodbtn"
        android1:layout_width="wrap_content"
        android1:layout_height="wrap_content"
        android1:layout_alignParentBottom="true"
        android1:layout_marginBottom="23dp"
        android1:layout_marginRight="24dp"
        android1:text="DRINKS ORDERS" />


    <LinearLayout
        android:id="@+id/top_layover"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:orientation="horizontal" >

        <TextView
            android1:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:gravity="center"
            android:text="@string/foodtitle"
            android:textAppearance="?android:attr/textAppearanceLarge" />

    </LinearLayout>

    <ListView
        android:id="@android:id/list"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/top_layover"
        android1:layout_alignBottom="@+id/servicesdelivered"
        android:background="#fff"
        android:divider="@android:color/transparent"
        android:scrollbars="none" />

    <LinearLayout
        android:id="@+id/bottom_layover"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:orientation="horizontal"
        android:weightSum="2" >

        <LinearLayout
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:orientation="vertical" >

        </LinearLayout>

        <LinearLayout
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:orientation="vertical" >



        </LinearLayout>
    </LinearLayout>

</RelativeLayout>

---

如果您需要更多的编码来发现错误，请告诉我！：）

假设第71行就是这个-

z.setOnClickListener(this);

此行必须将

z

设置为空

View z = findViewById(R.id.drinksbtn);

仔细检查

food

布局是否包含id为

drinksbtn

且无打字错误的视图

---

请注意，您的xml中没有

drinksbtn

，也没有

foodbutton

两者都没有。

z.setOnClickListener（这个）；很可能

z

为空-我怀疑

findViewById

返回了空。你应该检查一下-它真的是一个视图吗？@ChanYiQi post

food.xml

@ChanYiQi你的xml文件中没有名为drinksbtn的按钮。所以findViewById返回null。谢谢！这是我愚蠢的错误。

z.setOnClickListener(this);

View z = findViewById(R.id.drinksbtn);