android - 将数据从数据库检索到 ListView 失败

Question

我的程序包含一个Activity class 和一个数据库class。我用来将数据库值保存到 ListView 的代码有一些问题。 以下是Activity中的一个内部类:

class getclicker extends ListActivity implements Button.OnClickListener {
    public void onClick(View v) {

        String datevalue = date.getText().toString();
        String Userselectvalue = userSelection.getText().toString();
        cursor1 = eventsData.getContact(datevalue, Userselectvalue);
        String[] fromColumns = { classdbOpenHelper.KEY_EVENT };
        int[] toViews = { R.id.event };
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.events, cursor1, fromColumns, toViews, 0);
        listView = getListView();
        listView.setAdapter(adapter);

    }

    public void onDestroy() {
        eventsData.close();
    }
}

sqlite类包含

public Cursor getContact(String datevalue, String Userselectvalue) {
    String selection = classdbOpenHelper.KEY_DESC + " = '" + Userselectvalue + "'" + " AND " + classdbOpenHelper.KEY_DATE + " = '" + datevalue + "'";

    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.query(classdbOpenHelper.DATABASE_TABLE, new String[] { classdbOpenHelper.KEY_ROWID, classdbOpenHelper.KEY_DESC, classdbOpenHelper.KEY_EVENT, classdbOpenHelper.KEY_DATE },
            selection, null, null, null, null);
    if (cursor != null) {
        cursor.moveToFirst();
    }
    return cursor;
}

Answer 1

遵循我的代码

将以下内容写入layout/main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/hello"
    />
</LinearLayout>

将以下内容写入DBHelper.java:

package com.example.ListViewFromSQLiteDB;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;

public class DBHelper extends SQLiteOpenHelper{

    public SQLiteDatabase DB;
    public String DBPath;
    public static String DBName = "sample";
    public static final int version = '1';
    public static Context currentContext;
    public static String tableName = "Resource";


    public DBHelper(Context context) {
        super(context, DBName, null, version);
        currentContext = context;
        DBPath = "/data/data/" + context.getPackageName() + "/databases";
        createDatabase();

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub

    }

    private void createDatabase() {
        boolean dbExists = checkDbExists();

        if (dbExists) {
            // do nothing
        } else {
            DB = currentContext.openOrCreateDatabase(DBName, 0, null);
            DB.execSQL("CREATE TABLE IF NOT EXISTS " +
                    tableName +
                    " (LastName VARCHAR, FirstName VARCHAR," +
                    " Country VARCHAR, Age INT(3));");

            DB.execSQL("INSERT INTO " +
                    tableName +
                    " Values ('M','shumi','India',25);");
            DB.execSQL("INSERT INTO " +
                    tableName +
                    " Values ('C','sarah','India',25);");
            DB.execSQL("INSERT INTO " +
                    tableName +
                    " Values ('D','Lavya','USA',20);");
            DB.execSQL("INSERT INTO " +
                    tableName +
                    " Values ('V','Avi','EU',25);");
            DB.execSQL("INSERT INTO " +
                    tableName +
                    " Values ('T','Shenoi','Bangla',25);");
            DB.execSQL("INSERT INTO " +
                    tableName +
                    " Values ('L','Lamha','Australia',20);");
        }


    }

    private boolean checkDbExists() {
        SQLiteDatabase checkDB = null;

        try {
            String myPath = DBPath + DBName;
            checkDB = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READONLY);

        } catch (SQLiteException e) {

            // database does't exist yet.

        }

        if (checkDB != null) {

            checkDB.close();

        }

        return checkDB != null ? true : false;
    }
}

将以下内容写入您的 list 文件:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.example.ListViewFromSQLiteDB"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name="com.example.ListViewFromSQLiteDB.DataListView"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>

</manifest>

ListViewFromSQLiteDB.java 文件并在其中写入以下代码:

package com.example.ListViewFromSQLiteDB;

import java.util.ArrayList;

import android.app.ListActivity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.os.Bundle;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.TextView;

public class DataListView extends ListActivity {

    private ArrayList<String> results = new ArrayList<String>();
    private String tableName = DBHelper.tableName;
    private SQLiteDatabase newDB;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        openAndQueryDatabase();

        displayResultList();


    }
    private void displayResultList() {
        TextView tView = new TextView(this);
        tView.setText("This data is retrieved from the database and only 4 " +
                "of the results are displayed");
        getListView().addHeaderView(tView);

        setListAdapter(new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, results));
        getListView().setTextFilterEnabled(true);

    }
    private void openAndQueryDatabase() {
        try {
            DBHelper dbHelper = new DBHelper(this.getApplicationContext());
            newDB = dbHelper.getWritableDatabase();
            Cursor c = newDB.rawQuery("SELECT FirstName, Age FROM " +
                    tableName +
                    " where Age > 10 LIMIT 4", null);

            if (c != null ) {
                if  (c.moveToFirst()) {
                    do {
                        String firstName = c.getString(c.getColumnIndex("FirstName"));
                        int age = c.getInt(c.getColumnIndex("Age"));
                        results.add("Name: " + firstName + ",Age: " + age);
                    }while (c.moveToNext());
                } 
            }           
        } catch (SQLiteException se ) {
            Log.e(getClass().getSimpleName(), "Could not create or Open the database");
        } finally {
            if (newDB != null) 
                newDB.execSQL("DELETE FROM " + tableName);
                newDB.close();
        }

    }

}

现在只需运行代码....