Question

我正在为列表视图制作一个自定义适配器并获得NPE。我已经读过其他问题，但没有一个问题。这是logcat

07-04 06:54:58.036: E/AndroidRuntime(1340): FATAL EXCEPTION: main
07-04 06:54:58.036: E/AndroidRuntime(1340): java.lang.NullPointerException
07-04 06:54:58.036: E/AndroidRuntime(1340):     at com.example.amirkh.MainActivity$FastFoodAdapter.getView(MainActivity.java:166)
07-04 06:54:58.036: E/AndroidRuntime(1340):     at android.widget.AbsListView.obtainView(AbsListView.java:2159)
07-04 06:54:58.036: E/AndroidRuntime(1340):     at android.widget.ListView.measureHeightOfChildren(ListView.java:1246)
07-04 06:54:58.036: E/AndroidRuntime(1340):     at android.widget.ListView.onMeasure(ListView.java:1158)
07-04 06:54:58.036: E/AndroidRuntime(1340):     at android.view.View.measure(View.java:15518)
07-04 06:54:58.036: E/AndroidRuntime(1340):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
07-04 06:54:58.036: E/AndroidRuntime(1340):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
07-04 06:54:58.036: E/AndroidRuntime(1340):     at android.widget.TableRow.measureChildBeforeLayout(TableRow.java:247)

代码以这种方式工作。有一个数据库处理程序，它组织数据库，快餐类和主类。在主类中，用户输入快餐名称，然后转到数据库。当用户点击“显示数据”选项卡时，应显示整个数据。这是主要的课程：

package com.example.amirkh;

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

import android.R.integer;
import android.R.menu;
import android.os.Bundle;
import android.app.Activity;
import android.app.TabActivity;
import android.content.Context;
import android.content.Intent;
import android.graphics.drawable.Drawable;
import android.view.ActionProvider;
import android.view.ContextMenu;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.SubMenu;
import android.view.View;
import android.view.ViewGroup;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.MenuItem.OnActionExpandListener;
import android.view.MenuItem.OnMenuItemClickListener;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ExpandableListView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TabHost;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends TabActivity {
private TabHost myTabHost;
private FastFoodAdapter<String> adpter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    myTabHost = getTabHost();
    TabHost.TabSpec spec;

    // Adding First Tab
    spec = myTabHost.newTabSpec("first");
    spec.setContent(R.id.inputtab);
    spec.setIndicator("Input data");

    myTabHost.addTab(spec);

    // Adding Second Tab
    spec = myTabHost.newTabSpec("second");
    spec.setContent(R.id.listView1);
    spec.setIndicator("Show data");
    myTabHost.addTab(spec);
    myTabHost.setCurrentTab(0);

    // final List<FastFood> fflist = new ArrayList<FastFood>();
    final EditText etname = (EditText) findViewById(R.id.etname);
    final EditText etaddress = (EditText) findViewById(R.id.etaddress);
    final ListView lv = (ListView) findViewById(R.id.listView1);
    final DataBaseHandeler dbh = new DataBaseHandeler(MainActivity.this);
    final RadioGroup radiogroup = (RadioGroup) findViewById(R.id.radioGroup1);
    final FastFood fastfood = new FastFood();
    final RadioButton rbsit = (RadioButton) findViewById(R.id.rbsit);
    final RadioButton rbdeli = (RadioButton) findViewById(R.id.rbdeliv);
    final RadioButton rbtake = (RadioButton) findViewById(R.id.rbtake);
    refreshComponents();

    Button save = (Button) findViewById(R.id.btnsave);
    Button remove = (Button) findViewById(R.id.btnremove);

    // Create context menu
    registerForContextMenu(lv);

    // end of context menu

    // start of save button
    save.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            FastFood ffastfood = new FastFood("", "", "");
            ffastfood.setName(etname.getText().toString());
            ffastfood.setAddress(etaddress.getText().toString());

            etname.setText("");
            etaddress.setText("");

            if (rbsit.isChecked()) {
                ffastfood.setFlag("1");
            } else if (rbtake.isChecked()) {
                ffastfood.setFlag("2");
            } else if (rbdeli.isChecked()) {
                ffastfood.setFlag("3");
            }
            Toast toast = Toast.makeText(MainActivity.this,
                    "Fastfood is saved.", 2000);
            toast.setGravity(Gravity.CENTER, 0, 0);
            toast.show();

            dbh.addFastFood(ffastfood);
            refreshComponents();

        }
    }); // end of save

    // remove
    remove.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            EditText etrmvid = (EditText) findViewById(R.id.etrmvid);
            dbh.removeFastFood(Integer.parseInt(etrmvid.getText()
                    .toString()));
            etrmvid.setText("");
            Toast toast = Toast.makeText(MainActivity.this,
                    "Fastfood is removed.", 2000);
            toast.setGravity(Gravity.CENTER, 0, 0);
            toast.show();
            refreshComponents();

        }
    });// end of remove
    Context context = getApplicationContext();

    // Adapter
        }

        class FastFoodAdapter<String> extends ArrayAdapter<String> {
            public FastFood fastfood = new FastFood();

            public FastFoodAdapter(Context context, int textViewResourceId,
                    List objects) {
                super(context, textViewResourceId, objects);

                // TODO Auto-generated constructor stub
            }

            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                // TODO Auto-generated method stub

                  if (convertView == null)
                  {
                      LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                      View row = inflater.inflate(R.layout.listview_item_row, parent,
                                false);
                      }


                LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                View row = inflater.inflate(R.layout.listview_item_row, parent,
                        false);
                TextView tv = (TextView) row.findViewById(R.id.txtTitle23);
                TextView tv2 = (TextView) row.findViewById(R.id.txtTitle2);
                ImageView iv = (ImageView) row.findViewById(R.id.imgIcon);
                tv.setText(fastfood.getName());
                tv2.setText(fastfood.getAddress());
                if (fastfood.getFlag().equals("1"))
                    iv.setImageResource(R.drawable.sit);
                else if (fastfood.getFlag().equals("2"))
                    iv.setImageResource(R.drawable.ta);
                else if (fastfood.getFlag().equals("3"))
                    iv.setImageResource(R.drawable.deli);

                return row;
            }
        }// /end of adapter

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

public void onCreateContextMenu(ContextMenu menu, View v,
        ContextMenuInfo menuInfo) {
    getMenuInflater().inflate(R.menu.contexmenu, menu);
    super.onCreateContextMenu(menu, v, menuInfo);
}

@Override
public boolean onContextItemSelected(MenuItem item) {

    return super.onContextItemSelected(item);
}

private void refreshComponents() {

    ListView lv = (ListView) findViewById(R.id.listView1);
    TextView lblCount = (TextView) findViewById(R.id.lblcount);
    DataBaseHandeler dbh = new DataBaseHandeler(MainActivity.this);
    List<FastFood> fflist = dbh.getAllFastFoods();
    // lv.setAdapter(new FastFoodAdapter<String>(context,
    // textViewResourceId, objects))

    lv.setAdapter(new FastFoodAdapter<FastFood>(MainActivity.this,
            android.R.layout.simple_list_item_1, fflist));
    lblCount.setText("Count of all FastFoods are " + dbh.getFastFoodCount());
}
}

这里是快餐类

package com.example.amirkh;

public class FastFood {
private String name;
private String address;
private String flag;
private int id;

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getFlag() {
    return flag;
}

public void setFlag(String flag) {
    this.flag = flag;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}
public String getAddress() {
    return address;
}
public void setAddress(String address) {
    this.address = address;
}


public FastFood(String name, String address, String phone) {
    super();
    this.name = name;
    this.address = address;

}
public FastFood() {
    // TODO Auto-generated constructor stub
}

@Override
public String toString() {
    return (String.format("%s %s ", getName(), getAddress()));
}

}

和databasehandeler

package com.example.amirkh;

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

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class DataBaseHandeler extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "FastFoodManager";
private static final String TABALE_FASTFOODS = "fastfoods";
private static final String KEY_ID = "_id";
private static final String KEY_NAME = "name";
private static final String KEY_ADDRESS = "address";
private static final String KEY_FLAG = "flag";

public DataBaseHandeler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    // TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE IF NOT EXISTS " + TABALE_FASTFOODS + " ("
            + KEY_ID + " INTEGER PRIMARY KEY, " + KEY_NAME + " TEXT, "
            + KEY_ADDRESS + " TEXT, " + KEY_FLAG + " TEXT);");

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // TODO Auto-generated method stub
    db.execSQL("DROP TABLE IF EXISTS " + TABALE_FASTFOODS);
    onCreate(db);

}

// insert a record
public void addFastFood(FastFood fastfood) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(KEY_NAME, fastfood.getName());
    values.put(KEY_ADDRESS, fastfood.getAddress());
    values.put(KEY_FLAG, fastfood.getFlag());

    db.insert(TABALE_FASTFOODS, null, values);
    db.close();

}

// remove a record by ID
public void removeFastFood(int id) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABALE_FASTFOODS, KEY_ID + " =?",
            new String[] { String.valueOf(id) });
    db.close();
}

// count
public int getFastFoodCount() {
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery("SELECT * FROM " + TABALE_FASTFOODS, null);
    // db.close();
    return cursor.getCount();
}

// get all contacts
public List<FastFood> getAllFastFoods() {
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery("SELECT * FROM " + TABALE_FASTFOODS, null);
    List<FastFood> fflist = new ArrayList<FastFood>();
    if (cursor.moveToFirst()) {
        do {
            FastFood ff = new FastFood();
            ff.setId(Integer.parseInt(cursor.getString(0)));
            ff.setName(cursor.getString(1));
            ff.setAddress(cursor.getString(2));
            ff.setFlag(cursor.getString(3));
            fflist.add(ff);
        } while (cursor.moveToNext());
    }
    // db.close();
    return fflist;
}
}

感谢您的帮助

Answer 1

您的NPE来自：

if (fastfood.getFlag().equals("1"))

所以fastfood.getFlag()似乎是空的。您应该先使用setFlag()或尝试此比较：

if ("1".equals(fastfood.getFlag()))

Answer 2

您收到此NullPointerException是因为您试图比较此行中的null String

fastfood.getFlag().equals("1")

在适配器中，使用

创建Food对象

public FastFood fastfood = new FastFood();

在Food类的空构造函数中，没有任何成员分配给任何成员String，所以当你尝试

时

fastfood.getFlag().equals("1")

您正尝试在equals对象上调用null方法。

所以你得到NullPointerException。

您应该使用在Food构造函数中传递的List中的FastFoodAdapter个对象。

带定制适配器的NPE

2 个答案: