如何在安卓中更新数据到 SQLite 数据库？
原文:https://www . geeksforgeeks . org/如何将数据更新为安卓中的 sqlite 数据库/
我们已经看到了如何在安卓中创建和添加数据到 SQLite 数据库，以及如何在安卓中从 SQLite 数据库读取数据。我们执行了不同的 SQL 查询来读写我们的数据到 SQLite 数据库。在本文中，我们将看一下在安卓中更新数据到 SQLite 数据库。
我们将在本文中构建什么？
我们将构建一个简单的应用程序，在其中我们已经添加并读取了数据。现在，我们将在一个新的活动中简单地更新我们的数据，我们可以看到更新的数据。下面给出了一个示例视频，以了解我们将在本文中做什么。注意，我们将使用 Java 语言来实现这个项目。
[https://media.geeksforgeeks.org/wp-content/uploads/20210217232314/Screenrecorder-2021-02-17-23-20-26-737.mp4](https://media.geeksforgeeks.org/wp-content/uploads/20210217232314/Screenrecorder-2021-02-17-23-20-26-737.mp4)分步实施
第 1 步 : 创建一个更新我们课程的新活动
因为我们想更新我们的课程，所以在这个过程中，我们将创建一个新的活动，我们将能够在 SQLite 数据库中更新我们的课程。要创建新活动，我们必须导航到应用程序> java >您的应用程序的包名>右键单击包名>新建>空活动并将您的活动命名为更新课程活动并创建新活动。确保选择空活动。
步骤 2:使用 activity_update_course.xml 文件
导航至应用程序> res >布局>activity _ update _ course . XML并添加以下代码。
可扩展标记语言
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".UpdateCourseActivity">
<!--Edit text to enter course name-->
<EditText
android:id="@+id/idEdtCourseName"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:hint="Enter course Name" />
<!--edit text to enter course duration-->
<EditText
android:id="@+id/idEdtCourseDuration"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:hint="Enter Course Duration" />
<!--edit text to display course tracks-->
<EditText
android:id="@+id/idEdtCourseTracks"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:hint="Enter Course Tracks" />
<!--edit text for course description-->
<EditText
android:id="@+id/idEdtCourseDescription"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:hint="Enter Course Description" />
<!--button for updating our course-->
<Button
android:id="@+id/idBtnUpdateCourse"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:text="Update Course"
android:textAllCaps="false" />
</LinearLayout>
第三步:更新我们的 DBHandler 类
导航到应用程序> java >你的应用程序的包名> DBHandler 并添加下面的代码。在这种情况下，我们只需创建一种新的方法来更新我们的课程。
Java 语言(一种计算机语言，尤用于创建网站)
// below is the method for updating our courses
public void updateCourse(String originalCourseName, String courseName, String courseDescription,
String courseTracks, String courseDuration) {
// calling a method to get writable database.
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
// on below line we are passing all values
// along with its key and value pair.
values.put(NAME_COL, courseName);
values.put(DURATION_COL, courseDuration);
values.put(DESCRIPTION_COL, courseDescription);
values.put(TRACKS_COL, courseTracks);
// on below line we are calling a update method to update our database and passing our values.
// and we are comparing it with name of our course which is stored in original name variable.
db.update(TABLE_NAME, values, "name=?", new String[]{originalCourseName});
db.close();
}
以下是添加上述代码片段后DBHandler.java文件的更新代码。
Java 语言(一种计算机语言，尤用于创建网站)
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;
public class DBHandler extends SQLiteOpenHelper {
// creating a constant variables for our database.
// below variable is for our database name.
private static final String DB_NAME = "coursedb";
// below int is our database version
private static final int DB_VERSION = 1;
// below variable is for our table name.
private static final String TABLE_NAME = "mycourses";
// below variable is for our id column.
private static final String ID_COL = "id";
// below variable is for our course name column
private static final String NAME_COL = "name";
// below variable id for our course duration column.
private static final String DURATION_COL = "duration";
// below variable for our course description column.
private static final String DESCRIPTION_COL = "description";
// below variable is for our course tracks column.
private static final String TRACKS_COL = "tracks";
// creating a constructor for our database handler.
public DBHandler(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}
// below method is for creating a database by running a sqlite query
@Override
public void onCreate(SQLiteDatabase db) {
// on below line we are creating
// an sqlite query and we are
// setting our column names
// along with their data types.
String query = "CREATE TABLE " + TABLE_NAME + " ("
+ ID_COL + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ NAME_COL + " TEXT,"
+ DURATION_COL + " TEXT,"
+ DESCRIPTION_COL + " TEXT,"
+ TRACKS_COL + " TEXT)";
// at last we are calling a exec sql
// method to execute above sql query
db.execSQL(query);
}
// this method is use to add new course to our sqlite database.
public void addNewCourse(String courseName, String courseDuration, String courseDescription, String courseTracks) {
// on below line we are creating a variable for
// our sqlite database and calling writable method
// as we are writing data in our database.
SQLiteDatabase db = this.getWritableDatabase();
// on below line we are creating a
// variable for content values.
ContentValues values = new ContentValues();
// on below line we are passing all values
// along with its key and value pair.
values.put(NAME_COL, courseName);
values.put(DURATION_COL, courseDuration);
values.put(DESCRIPTION_COL, courseDescription);
values.put(TRACKS_COL, courseTracks);
// after adding all values we are passing
// content values to our table.
db.insert(TABLE_NAME, null, values);
// at last we are closing our
// database after adding database.
db.close();
}
// we have created a new method for reading all the courses.
public ArrayList<CourseModal> readCourses() {
// on below line we are creating a
// database for reading our database.
SQLiteDatabase db = this.getReadableDatabase();
// on below line we are creating a cursor with query to read data from database.
Cursor cursorCourses = db.rawQuery("SELECT * FROM " + TABLE_NAME, null);
// on below line we are creating a new array list.
ArrayList<CourseModal> courseModalArrayList = new ArrayList<>();
// moving our cursor to first position.
if (cursorCourses.moveToFirst()) {
do {
// on below line we are adding the data from cursor to our array list.
courseModalArrayList.add(new CourseModal(cursorCourses.getString(1),
cursorCourses.getString(4),
cursorCourses.getString(2),
cursorCourses.getString(3)));
} while (cursorCourses.moveToNext());
// moving our cursor to next.
}
// at last closing our cursor
// and returning our array list.
cursorCourses.close();
return courseModalArrayList;
}
// below is the method for updating our courses
public void updateCourse(String originalCourseName, String courseName, String courseDescription,
String courseTracks, String courseDuration) {
// calling a method to get writable database.
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
// on below line we are passing all values
// along with its key and value pair.
values.put(NAME_COL, courseName);
values.put(DURATION_COL, courseDuration);
values.put(DESCRIPTION_COL, courseDescription);
values.put(TRACKS_COL, courseTracks);
// on below line we are calling a update method to update our database and passing our values.
// and we are comparing it with name of our course which is stored in original name variable.
db.update(TABLE_NAME, values, "name=?", new String[]{originalCourseName});
db.close();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// this method is called to check if the table exists already.
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
}
版权属于：月萌API www.moonapi.com，转载请注明出处
