请查看以下代码
Form.java
Form.java是Main活动，表示第一页的Java文件。许多与创建“列表”和菜单相关的代码都将被删除。
package com.example.esoftcallmanager;
import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.Context;
import android.content.DialogInterface;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class Form extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_form);
DatabaseConnector databaseConnector = new DatabaseHandler();
databaseConnector.createConnection();
ListView lv = (ListView)findViewById(android.R.id.list);
String arr[] = getResources().getStringArray(R.array.branch_list);
//lv.setAdapter(new MyAdapter(this,android.R.layout.simple_list_item_1,R.id.listText,arr));
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
// TODO Auto-generated method stub
}
});
}
}
DataBaseConnector.java
这是代码的接口，用于执行数据库操作
package com.example.esoftcallmanager;
public interface DatabaseConnector
{
public void createConnection();
public void closeConnection();
public String getPhoneNumber();
}
DataBaseHandler.java
这是执行数据库操作的
package com.example.esoftcallmanager;
import android.app.Activity;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.widget.Toast;
public class DatabaseHandler extends Activity implements DatabaseConnector
{
private SQLiteDatabase database;
private String dbPath = "data//data//com.example.esoftcallmanager.sqllite//esoftDatabase";
@Override
public void createConnection()
{
try
{
database = this.openOrCreateDatabase("esoftDatabase", MODE_PRIVATE, null);
database.execSQL("create table BranchNetwork(" +
"brID integer primary key autoincrement,"
+"city text,"
+"steetAddress text"
+"phoneNumber1 text"
+"phoneNumber2 text"
+"email text"
+");");
}
catch(SQLException sql)
{
Toast.makeText(this, sql.getMessage(), Toast.LENGTH_LONG).show();
}
}
@Override
public void closeConnection() {
// TODO Auto-generated method stub
}
@Override
public String getPhoneNumber() {
// TODO Auto-generated method stub
return null;
}
}
但是，我无法运行代码，因为我收到以下错误。
02-11 20:35:59.350: D/dalvikvm(434): GC_EXTERNAL_ALLOC freed 52K, 53% free 2552K/5379K, external 1949K/2137K, paused 80ms
02-11 20:40:34.021: D/dalvikvm(1131): GC_EXTERNAL_ALLOC freed 42K, 53% free 2552K/5379K, external 1949K/2137K, paused 122ms
02-11 20:40:34.361: D/AndroidRuntime(1131): Shutting down VM
02-11 20:40:34.361: W/dalvikvm(1131): threadid=1: thread exiting with uncaught exception (group=0x40015560)
02-11 20:40:34.401: E/AndroidRuntime(1131): FATAL EXCEPTION: main
02-11 20:40:34.401: E/AndroidRuntime(1131): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.esoftcallmanager/com.example.esoftcallmanager.Form}: java.lang.NullPointerException
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.os.Handler.dispatchMessage(Handler.java:99)
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.os.Looper.loop(Looper.java:123)
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.app.ActivityThread.main(ActivityThread.java:3683)
02-11 20:40:34.401: E/AndroidRuntime(1131): at java.lang.reflect.Method.invokeNative(Native Method)
02-11 20:40:34.401: E/AndroidRuntime(1131): at java.lang.reflect.Method.invoke(Method.java:507)
02-11 20:40:34.401: E/AndroidRuntime(1131): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
02-11 20:40:34.401: E/AndroidRuntime(1131): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
02-11 20:40:34.401: E/AndroidRuntime(1131): at dalvik.system.NativeStart.main(Native Method)
02-11 20:40:34.401: E/AndroidRuntime(1131): Caused by: java.lang.NullPointerException
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
02-11 20:40:34.401: E/AndroidRuntime(1131): at com.example.esoftcallmanager.DatabaseHandler.createConnection(DatabaseHandler.java:19)
02-11 20:40:34.401: E/AndroidRuntime(1131): at com.example.esoftcallmanager.Form.onCreate(Form.java:30)
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-11 20:40:34.401: E/AndroidRuntime(1131): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
02-11 20:40:34.401: E/AndroidRuntime(1131): ... 11 more
02-11 20:40:37.381: I/Process(1131): Sending signal. PID: 1131 SIG: 9
每当我从Form.java中删除数据库连接部分时，这都可以正常工作！所以错误必须在以下代码中
DatabaseConnector databaseConnector = new DatabaseHandler();
databaseConnector.createConnection();
我不想在Form.java中添加所有数据库操作。我需要像我一样分开工作。但是，我该怎么做？请帮忙！
答案 0 :(得分：2)
我看到的一件事是：
database.execSQL("create table BranchNetwork(" +
"brID integer primary key autoincrement,"
+"city text,"
+"steetAddress text"
+"phoneNumber1 text"
+"phoneNumber2 text"
+"email text"
+");");
你必须写：
database.execSQL("create table BranchNetwork(" +
"brID integer primary key autoincrement,"
+"city text,"
+"steetAddress text," //forgot comma
+"phoneNumber1 text," //forgot comma
+"phoneNumber2 text," // forgot commas
+"email text"
+");");
我不知道这是不是错，但试试吧......
答案 1 :(得分：2)
如果DatabaseHandler不是Activity类，则无需将Activity扩展到它。您需要创建DatabaseHandler的参数化构造函数，以将Activity上下文传递给它以创建数据库。将您的DatabaseHandler类更改为：
public class DatabaseHandler implements DatabaseConnector
{
private SQLiteDatabase database;
....
Context context;
public DatabaseHandler(Context context){
this.context=context;
}
@Override
public void createConnection()
{
try
{
database = context.openOrCreateDatabase("esoftDatabase",
MODE_PRIVATE, null);
// your code here....
}
catch(SQLException sql)
{
Toast.makeText(context, sql.getMessage(),
Toast.LENGTH_LONG).show();
}
}
并从表单活动传递活动上下文：
DatabaseConnector databaseConnector =
new DatabaseHandler(Form.this);
databaseConnector.createConnection();