在我的代码中，当我搜索时，listview从database.i创建想要从here.i使用上下文菜单删除表。对于getter和setter，有一个Book.java文件。一切顺利，但当我按删除然后确定程序停止。我认为问题是在processDelete函数。我也无法从我的表中获取id，因为rowId是列表中的id。请快点帮帮我。没有这个，我什么也做不了。
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import android.app.AlertDialog;
import android.app.ListActivity;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;
public class EmployeeList extends ListActivity {
protected EditText searchText;
protected SQLiteDatabase db;
protected Cursor cursor;
protected ListAdapter adapter;
public Integer pid=null;
public DatabaseHelper databaseHelper=new DatabaseHelper(null); //my database(I gave parameter null because i don't know what to give)
public Book book; //getter setter
private static final int DELETE_ID = Menu.FIRST+3;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
db = (new DatabaseHelper(this)).getWritableDatabase();
searchText = (EditText) findViewById (R.id.searchText);
}
public void search(View view) {
// || is the concatenation operation in SQLite
Toast.makeText(getApplicationContext(), "insert successfull", Toast.LENGTH_LONG).show();
cursor = db.rawQuery("SELECT _id, firstName, lastName, title FROM employee WHERE firstName || ' ' || lastName LIKE ?",
new String[]{"%" + searchText.getText().toString() + "%"});
adapter = new SimpleCursorAdapter(
this,
R.layout.employee_list_item,
cursor,
new String[] {"firstName", "lastName", "title"},
new int[] {R.id.firstName, R.id.lastName, R.id.title});
setListAdapter(adapter);
registerForContextMenu(getListView());
}
public void onListItemClick(ListView parent, View view, int position, long id) {
Intent intent = new Intent(this, EmployeeDetails.class);
Cursor cursor = (Cursor) adapter.getItem(position);
intent.putExtra("EMPLOYEE_ID", cursor.getInt(cursor.getColumnIndex("_id"))); **strong text**
startActivity(intent);
}
public void onCreateContextMenu(ContextMenu menu, View v,
ContextMenu.ContextMenuInfo menuInfo) {
menu.add(Menu.NONE, DELETE_ID, Menu.NONE, "Delete")
.setAlphabeticShortcut('d');
}
@Override
public boolean onContextItemSelected(MenuItem item) {
switch (item.getItemId()) {
case DELETE_ID:
AdapterView.AdapterContextMenuInfo info=
(AdapterView.AdapterContextMenuInfo)item.getMenuInfo();
delete(info.id);
return(true);
}
return(super.onOptionsItemSelected(item));
}
private void delete(final long rowId) {
if (rowId>0) {
new AlertDialog.Builder(this)
.setTitle(R.string.delete_title)
.setPositiveButton(R.string.ok,
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int whichButton) {
processDelete(rowId);
}
})
.setNegativeButton(R.string.cancel,
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int whichButton) {
// ignore, just dismiss
}
})
.show();
}
}
private void processDelete(long rowId) { //I get exact rowid.
String[] args={String.valueOf(rowId)};
databaseHelper.getWritableDatabase().delete("employee", "_ID=?", args); //employee is table name and _ID is id column(here i get nullPointerException)
cursor.requery();
}
}`
数据库助手类：
` 公共类DatabaseHelper扩展了SQLiteOpenHelper {
public static final String DB_NAME = "employee_directory";
public static final Integer VERSION=1;
public static final String TABLE_NAME= "employee";
public static final String _id= "id";
public static final String firstName= "firstName";
public static final String lastName= "lastName";
public static final String title= "title";
public static final String officePhone= "officePhone";
public static final String cellPhone= "cellPhone";
public static final String email= "email";
public static final String TABLE_SQL = "CREATE TABLE " + TABLE_NAME+" (" +_id+" INTEGER PRIMARY KEY AUTOINCREMENT, "
+ firstName+ " TEXT, " + lastName+ " TEXT, " + title+ " TEXT, " + officePhone+ " TEXT, " + cellPhone+" TEXT, " + email+" TEXT)";
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, VERSION);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
Log.d("TABLE SQL", TABLE_SQL);
db.execSQL(TABLE_SQL);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldV, int newV) {
db.execSQL("DROP TABLE IF EXISTS employees");
onCreate(db);
}
// public void delete(int pos) {
// SQLiteDatabase db = this.getWritableDatabase();
// db.delete(TABLE_NAME, _id + " = ?",
// new String[] { String.valueOf(pos)});
// db.close();
// }
//public void delete(String value1) {
// TODO Auto-generated method stub
// getWritableDatabase().delete(TABLE_NAME, "id=?", new String[] { value1 });
//}
}`
Logcat说我收到了NullPointerException。我的删除查询中有什么问题吗？
logcat的：
`
07-28 20:10:23.384: E/AndroidRuntime(977): FATAL EXCEPTION: main
07-28 20:10:23.384: E/AndroidRuntime(977): java.lang.NullPointerException
07-28 20:10:23.384: E/AndroidRuntime(977): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
07-28 20:10:23.384: E/AndroidRuntime(977): at com.example.intent.EmployeeList.processDelete(EmployeeList.java:124)
07-28 20:10:23.384: E/AndroidRuntime(977): at com.example.intent.EmployeeList.access$0(EmployeeList.java:115)
07-28 20:10:23.384: E/AndroidRuntime(977): at com.example.intent.EmployeeList$1.onClick(EmployeeList.java:101)
07-28 20:10:23.384: E/AndroidRuntime(977): at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:158)
07-28 20:10:23.384: E/AndroidRuntime(977): at android.os.Handler.dispatchMessage(Handler.java:99)
07-28 20:10:23.384: E/AndroidRuntime(977): at android.os.Looper.loop(Looper.java:123)
07-28 20:10:23.384: E/AndroidRuntime(977): at android.app.ActivityThread.main(ActivityThread.java:4627)
07-28 20:10:23.384: E/AndroidRuntime(977): at java.lang.reflect.Method.invokeNative(Native Method)
07-28 20:10:23.384: E/AndroidRuntime(977): at java.lang.reflect.Method.invoke(Method.java:521)
07-28 20:10:23.384: E/AndroidRuntime(977): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
07-28 20:10:23.384: E/AndroidRuntime(977): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
07-28 20:10:23.384: E/AndroidRuntime(977): at dalvik.system.NativeStart.main(Native Method)
`
通过插入这些来解决这些问题。但仍有一些错误。
08-09 02:09:52.955: E/Database(310): close() was never explicitly called on database '/data/data/com.example.intent/databases/employee_directory'
08-09 02:09:52.955: E/Database(310): android.database.sqlite.DatabaseObjectNotClosedException: Application did not close the cursor or database object that was opened here
08-09 02:09:52.955: E/Database(310): at android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1810)
08-09 02:09:52.955: E/Database(310): at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:817)
08-09 02:09:52.955: E/Database(310): at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:851)
08-09 02:09:52.955: E/Database(310): at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:844)
08-09 02:09:52.955: E/Database(310): at android.app.ContextImpl.openOrCreateDatabase(ContextImpl.java:540)
08-09 02:09:52.955: E/Database(310): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
08-09 02:09:52.955: E/Database(310): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
08-09 02:09:52.955: E/Database(310): at com.example.intent.EmployeeList.onCreate(EmployeeList.java:44)
08-09 02:09:52.955: E/Database(310): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-09 02:09:52.955: E/Database(310): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
08-09 02:09:52.955: E/Database(310): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
08-09 02:09:52.955: E/Database(310): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
08-09 02:09:52.955: E/Database(310): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
08-09 02:09:52.955: E/Database(310): at android.os.Handler.dispatchMessage(Handler.java:99)
08-09 02:09:52.955: E/Database(310): at android.os.Looper.loop(Looper.java:123)
08-09 02:09:52.955: E/Database(310): at android.app.ActivityThread.main(ActivityThread.java:4627)
08-09 02:09:52.955: E/Database(310): at java.lang.reflect.Method.invokeNative(Native Method)
08-09 02:09:52.955: E/Database(310): at java.lang.reflect.Method.invoke(Method.java:521)
08-09 02:09:52.955: E/Database(310): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-09 02:09:52.955: E/Database(310): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-09 02:09:52.955: E/Database(310): at dalvik.system.NativeStart.main(Native Method)
我将如何解决光标问题？
答案 0 :(得分：1)
创建数据库助手时，请调用
public DatabaseHelper databaseHelper=new DatabaseHelper(null);
但null错了。如果您查看有关Context的文档，您会看到Activity是已知的间接子类。您当前的活动是此处的上下文：
public DatabaseHelper databaseHelper=new DatabaseHelper(this);
修改
作为构造函数定义
public DatabaseHelper(Context context)
告诉我，创建Context需要DatabaseHelper类型的参数。 Context对象提供有关特定应用程序的信息，并提供与应用程序相关的服务。
可以使用类似于例如子类的Context对象而不是ListActivity。 ListActivity。在文档中，您可以看到Activity扩展ContextThemeWrapper，后者又扩展Context，依此扩展到Context。在需要EmployeeList对象作为参数的情况下，可以使用其中一个类的每个对象（至少在形式上，根据用例，可能存在在实践中不起作用的对象）。
您的ListActivity扩展this，因此也可以用作上下文。方法中的关键字obj.foo()
始终引用调用方法的对象，例如，在电话中
thisfoo()中的 obj则表示this引用的同一个对象。
在开头的特定情况下，EmployeeList引用{{1}}对象。