Android 由于ClassCastException,应用程序在启动时崩溃
当我启动我的应用程序时,我在Android 由于ClassCastException,应用程序在启动时崩溃,android,sqlite,crash,Android,Sqlite,Crash,当我启动我的应用程序时,我在Cursor c=(Cursor)DataHelper.selectAll()处得到一个ClassCastException 以下是我的主要.java: package com.gantt.shoppinglist; import android.app.Dialog; import android.app.ListActivity; import android.database.Cursor; import android.os.Bundle; import a
Cursor c=(Cursor)DataHelper.selectAll()处得到一个ClassCastException代码>
以下是我的主要.java:
package com.gantt.shoppinglist;
import android.app.Dialog;
import android.app.ListActivity;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
public class ShoppingList extends ListActivity {
private DataHelper DataHelper;
/** Called when the activity is first created. */
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DataHelper = new DataHelper(this);
ListView listview = (ListView) findViewById(android.R.id.list);
Cursor c = (Cursor) DataHelper.selectAll();
startManagingCursor(c);
String[] from = new String[] { com.gantt.shoppinglist.DataHelper.getDatabaseName() };
int[] to = new int[] { android.R.id.text1 };
ListAdapter adapter = new SimpleCursorAdapter(this,
R.layout.rowlayout, c, from, to);
setListAdapter(adapter);
Button button1main = (Button) findViewById(R.id.add);
button1main.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
final Dialog additem = new Dialog(ShoppingList.this);
additem.setContentView(R.layout.maindialog);
final EditText et = (EditText)additem.findViewById(R.id.edittext);
additem.setTitle("Type your item");
additem.setCancelable(true);
et.setHint("Type the name of an item...");
Button button = (Button) additem.findViewById(R.id.cancel);
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
additem.dismiss();
}
});
additem.show();
Button ok = (Button) additem.findViewById(R.id.ok);
ok.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
final String text = et.getText().toString();
additem.dismiss();
et.setText("");
}
});
}
});
}
}
我的DataHelper类:
package com.gantt.shoppinglist;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteStatement;
import android.util.Log;
public class DataHelper {
private static final String DATABASE_NAME = "items.db";
private static final int DATABASE_VERSION = 1;
private static final String TABLE_NAME = "table1";
private Context context;
private SQLiteDatabase db;
private SQLiteStatement insertStmt;
private static final String INSERT = "insert into "
+ TABLE_NAME + "(name) values (?)";
public DataHelper(Context context) {
this.context = context;
OpenHelper openHelper = new OpenHelper(this.context);
this.db = openHelper.getWritableDatabase();
this.insertStmt = this.db.compileStatement(INSERT);
}
public long insert(String name) {
this.insertStmt.bindString(1, name);
return this.insertStmt.executeInsert();
}
public void deleteAll() {
this.db.delete(TABLE_NAME, null, null);
}
public List<String> selectAll() {
List<String> list = new ArrayList<String>();
Cursor cursor = this.db.query(TABLE_NAME, new String[] { "name" },
null, null, null, null, "name desc");
if (cursor.moveToFirst()) {
do {
list.add(cursor.getString(0));
} while (cursor.moveToNext());
}
if (cursor != null && !cursor.isClosed()) {
cursor.close();
}
return list;
}
public static String getDatabaseName() {
return DATABASE_NAME;
}
private static class OpenHelper extends SQLiteOpenHelper {
OpenHelper(Context context) {
super(context, getDatabaseName(), null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE " + TABLE_NAME + "(id INTEGER PRIMARY KEY, name TEXT);");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w("Example", "Upgrading database, this will drop tables and recreate.");
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
}
}
package com.gantt.shoppinglist;
导入java.util.ArrayList;
导入java.util.List;
导入android.content.Context;
导入android.database.Cursor;
导入android.database.sqlite.SQLiteDatabase;
导入android.database.sqlite.SQLiteOpenHelper;
导入android.database.sqlite.SQLiteStatement;
导入android.util.Log;
公共类DataHelper{
私有静态最终字符串数据库\u NAME=“items.db”;
私有静态最终int数据库_VERSION=1;
私有静态最终字符串表\u NAME=“table1”;
私人语境;
专用数据库数据库;
私有SQLiteStatement insertStmt;
私有静态最终字符串INSERT=“插入到”
+表_NAME+“(NAME)值(?);
公共DataHelper(上下文){
this.context=上下文;
OpenHelper OpenHelper=新的OpenHelper(this.context);
this.db=openHelper.getWritableDatabase();
this.insertStmt=this.db.compileStatement(INSERT);
}
公共长插入(字符串名称){
this.insertStmt.bindString(1,名称);
返回此.insertStmt.executeInsert();
}
public void deleteAll(){
this.db.delete(表名称,null,null);
}
公共列表selectAll(){
列表=新的ArrayList();
Cursor Cursor=this.db.query(表名,新字符串[]{“NAME”},
空,空,空,空,“名称描述”);
if(cursor.moveToFirst()){
做{
list.add(cursor.getString(0));
}while(cursor.moveToNext());
}
if(cursor!=null&!cursor.isClosed()){
cursor.close();
}
退货清单;
}
公共静态字符串getDatabaseName(){
返回数据库名称;
}
私有静态类OpenHelper扩展了SQLiteOpenHelper{
OpenHelper(上下文){
super(上下文,getDatabaseName(),null,数据库版本);
}
@凌驾
public void onCreate(SQLiteDatabase db){
db.execSQL(“创建表”+表名+”(id整数主键,名称文本);”;
}
@凌驾
public void onUpgrade(SQLiteDatabase db,int-oldVersion,int-newVersion){
w(“示例”,“升级数据库,这将删除表并重新创建”);
db.execSQL(“如果存在删除表”+表名称);
onCreate(db);
}
}
}
您得到的是ClassCastException
,因为您试图将列表
强制转换为光标
,这在继承层次结构中不相关
看起来您正在混合来自ArrayAdapter
示例和CursorAdapter
示例的代码。如果希望selectAll()
返回List
,请更仔细地按照ArrayAdapter
示例操作。否则,请更改selectAll()
以返回光标
,并更仔细地遵循光标或适配器
示例。您得到的是ClassCastException
,因为您正试图将列表
强制转换为光标
,这在继承层次结构中不相关
看起来您正在混合来自ArrayAdapter
示例和CursorAdapter
示例的代码。如果希望selectAll()
返回List
,请更仔细地按照ArrayAdapter
示例操作。否则,更改selectAll()
以返回光标
,并更仔细地遵循CursorAdapter
示例。刚刚要发布相同的:)这就是我在中所说的……谢谢,我对这一点还是新手。实际上,我已经到了需要知道如何添加_id列的地步。我一直在查,到目前为止运气不好。我正要发同样的帖子:)这是我在中说的……谢谢,我对这一点还是新手。事实上,我已经到了需要弄清楚如何添加一个_id列的地步。我一直在查,到目前为止运气不好。