Question

当我启动应用程序时，我在Cursor c = (Cursor) DataHelper.selectAll();获得了ClassCastException。

这是我的主要.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);
          }
       }
    }

Answer 1

你得到的是ClassCastException，因为你试图将List<String>转换为Cursor，这与继承层次结构中没有关系。

您似乎在混合ArrayAdapter示例和CursorAdapter示例中的代码。如果您希望selectAll()返回List<String>，请更密切地关注ArrayAdapter示例。否则，请更改selectAll()以返回Cursor并更密切关注CursorAdapter示例。

由于ClassCastException，应用程序在启动时崩溃

1 个答案: