访问应用页面'CurrentItems'时，请关闭并显示以下错误：
01-21 19:51:54.474: E/AndroidRuntime(10418): FATAL EXCEPTION: main
01-21 19:51:54.474: E/AndroidRuntime(10418): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fooditemmonitor/com.example.fooditemmonitor.CurrentItems}: java.lang.NullPointerException
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.app.ActivityThread.access$700(ActivityThread.java:159)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.os.Handler.dispatchMessage(Handler.java:99)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.os.Looper.loop(Looper.java:176)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.app.ActivityThread.main(ActivityThread.java:5419)
01-21 19:51:54.474: E/AndroidRuntime(10418): at java.lang.reflect.Method.invokeNative(Native Method)
01-21 19:51:54.474: E/AndroidRuntime(10418): at java.lang.reflect.Method.invoke(Method.java:525)
01-21 19:51:54.474: E/AndroidRuntime(10418): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
01-21 19:51:54.474: E/AndroidRuntime(10418): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
01-21 19:51:54.474: E/AndroidRuntime(10418): at dalvik.system.NativeStart.main(Native Method)
01-21 19:51:54.474: E/AndroidRuntime(10418): Caused by: java.lang.NullPointerException
01-21 19:51:54.474: E/AndroidRuntime(10418): at com.example.fooditemmonitor.CurrentItems.updateTable(CurrentItems.java:65)
01-21 19:51:54.474: E/AndroidRuntime(10418): at com.example.fooditemmonitor.CurrentItems.onCreate(CurrentItems.java:34)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.app.Activity.performCreate(Activity.java:5372)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
01-21 19:51:54.474: E/AndroidRuntime(10418): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257)
01-21 19:51:54.474: E/AndroidRuntime(10418): ... 11 more
CurrentItems
package com.example.fooditemmonitor;
import java.util.ArrayList;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.View;
import android.widget.Button;
import android.widget.TableLayout;
import android.widget.TableRow;
import android.widget.TextView;
public class CurrentItems extends Activity {
ItemDatabase db;
Context context;
Button addButton;
// the table that displays the data
TableLayout dataTable;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.current_inventory);
db = new ItemDatabase(this);
// bring up current database items
updateTable();
// create references and listeners for the GUI interface
setupViews();
// make the buttons clicks perform actions
addButtonListeners();
}
private void setupViews() {
// THE DATA TABLE
dataTable = (TableLayout) findViewById(R.id.currentTable);
// THE BUTTONS
addButton = (Button) findViewById(R.id.scanCurrent);
}
private void addButtonListeners() {
addButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(CurrentItems.this, AddItem.class));
;
}
});
}
private void updateTable() {
// delete all but the first row. remember that the count starts at one
// and the index starts at zero
while (dataTable.getChildCount() > 1) {
// while there are at least two rows in the table widget, delete
// the second row.
dataTable.removeViewAt(1);
}
// collect the current row information from the database and
// store it in a two dimensional ArrayList
ArrayList<ArrayList<Object>> data = db.getAllRowsAsArrays();
// iterate the ArrayList, create new rows each time and add them
// to the table widget.
for (int position = 0; position < data.size(); position++) {
TableRow tableRow = new TableRow(this);
ArrayList<Object> row = data.get(position);
TextView dateData = new TextView(this);
dateData.setText(row.get(1).toString());
tableRow.addView(dateData);
TextView quantityData = new TextView(this);
quantityData.setText(row.get(4).toString());
tableRow.addView(quantityData);
TextView titleData = new TextView(this);
titleData.setText(row.get(3).toString());
tableRow.addView(titleData);
dataTable.addView(tableRow);
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.main, menu);
return super.onCreateOptionsMenu(menu);
}
}
ItemDatabase
package com.example.fooditemmonitor;
import java.util.ArrayList;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public final class ItemDatabase {
// the Activity or Application that is creating an object from this class.
Context context;
// a reference to the database used by this application/object
private SQLiteDatabase db;
// These constants are specific to the database.
private final String DATABASE_NAME = "ItemDatabase.sqlite";
private final int DATABASE_VERSION = 1;
// These constants are specific to the database table.
private final String TABLE_NAME = "foodItems";
private final String COLUMN_NAME_ENTRY_ID = "entryid";
private final String COLUMN_NAME_BARCODE = "barcode";
private final String COLUMN_NAME_TITLE = "title";
private final String COLUMN_NAME_QUANTITY = "quantity";
private final String COLUMN_NAME_DATE = "date";
public ItemDatabase(Context context) {
this.context = context;
// create or open the database
ItemDatabaseHelper helper = new ItemDatabaseHelper(context);
this.db = helper.getWritableDatabase();
}
public void addRow(String rowStringOne, String rowStringTwo,
String rowStringThree, int rowIntFour) {
// this is a key value pair holder used by android's SQLite functions
ContentValues values = new ContentValues();
values.put(COLUMN_NAME_DATE, rowStringOne);
values.put(COLUMN_NAME_BARCODE, rowStringTwo);
values.put(COLUMN_NAME_TITLE, rowStringThree);
values.put(COLUMN_NAME_QUANTITY, rowIntFour);
// ask the database object to insert the new data
try {
db.insert(TABLE_NAME, null, values);
} catch (Exception e) {
Log.e("DB ERROR", e.toString());
e.printStackTrace();
}
}
public void updateRow(long rowID, String rowStringOne, String rowStringTwo,
String rowStringThree, int rowIntFour) {
// this is a key value pair holder used by android's SQLite functions
ContentValues values = new ContentValues();
values.put(COLUMN_NAME_DATE, rowStringOne);
values.put(COLUMN_NAME_BARCODE, rowStringTwo);
values.put(COLUMN_NAME_TITLE, rowStringThree);
values.put(COLUMN_NAME_QUANTITY, rowIntFour);
// ask the database object to update the database row of given rowID
try {
db.update(TABLE_NAME, values, COLUMN_NAME_ENTRY_ID + "=" + rowID,
null);
} catch (Exception e) {
Log.e("DB Error", e.toString());
e.printStackTrace();
}
}
public void deleteRow(long rowID) {
// ask the database manager to delete the row of given id
try {
db.delete(TABLE_NAME, COLUMN_NAME_ENTRY_ID + "=" + rowID, null);
} catch (Exception e) {
Log.e("DB ERROR", e.toString());
e.printStackTrace();
}
}
public ArrayList<ArrayList<Object>> getAllRowsAsArrays() {
// create an ArrayList that will hold all of the data collected from
// the database.
ArrayList<ArrayList<Object>> dataArrays = new ArrayList<ArrayList<Object>>();
// this is a database call that creates a "cursor" object.
// the cursor object store the information collected from the
// database and is used to iterate through the data.
Cursor cursor;
try {
// ask the database object to create the cursor.
cursor = db.query(TABLE_NAME, new String[] { COLUMN_NAME_DATE,
COLUMN_NAME_QUANTITY, COLUMN_NAME_TITLE }, null, null,
null, null, COLUMN_NAME_TITLE + " DESC");
// move the cursor's pointer to position zero.
cursor.moveToFirst();
// if there is data after the current cursor position, add it to the
// ArrayList.
if (!cursor.isAfterLast()) {
do {
ArrayList<Object> dataList = new ArrayList<Object>();
dataList.add(cursor.getString(1));
dataList.add(cursor.getInt(4));
dataList.add(cursor.getString(3));
dataArrays.add(dataList);
}
// move the cursor's pointer up one position.
while (cursor.moveToNext());
}
} catch (SQLException e) {
Log.e("DB Error", e.toString());
e.printStackTrace();
}
// return the ArrayList that holds the data collected from the database.
return dataArrays;
}
public class ItemDatabaseHelper extends SQLiteOpenHelper {
public ItemDatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
String newTableQueryString = "create table " + TABLE_NAME + " ("
+ COLUMN_NAME_ENTRY_ID
+ " integer primary key autoincrement not null,"
+ COLUMN_NAME_DATE + " date," + COLUMN_NAME_BARCODE
+ " text," + COLUMN_NAME_TITLE + " text"
+ COLUMN_NAME_QUANTITY + " int" + ");";
// execute the query string to the database.
db.execSQL(newTableQueryString);
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
}
第65行：
while (dataTable.getChildCount() > 1) {
从显示的消息中，数据似乎正在进入数据库，但尝试访问它会导致错误。我没看到语法错误或拼写错误。
任何帮助将不胜感激。
答案 0 :(得分：1)
dataTable仅在您的应用中稍后初始化（setupViews()）。当你致电updateTable()时，它尚未初始化。
通常这些问题很容易自行调试。正如您已经找到导致NPE的代码行。在这种情况下，NPE代码行的唯一方法是dataTable为null时。然后回读代码以检查变量初始化的位置（如果有的话）以及何时发生，与NPE行相关。
此特定问题的修复很简单：只需在setupViews()中切换订单或updateTable()和onCreate()。
答案 1 :(得分：1)
在dataTable = (TableLayout) findViewById(R.id.currentTable);
updateTable()