在DatabaseTest项目的基础上继续开发
DatabaseTest项目见持久化技术——SQLite数据库存储
1. 创建内容提供器
右击com.example.databasetest包–>New–>Other–>Content Provider，将内容提供器命名为DatabaseProvider，authority指定为com.example.databasetest.provider，将Exported属性和Enable属性都选中。
package com.example.databasetest;
import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
public class DatabaseProvider extends ContentProvider {
public static final int BOOK_DIR = 0; //Book表中的所有数据
public static final int BOOK_ITEM = 1; //Book表中的单条数据
public static final int CATEGORY_DIR = 2; //Category表中的所有数据
public static final int CATEGORY_ITEM = 3; //Category表中的单条数据
public static final String AUTHORITY = "com.example.databasetest.provider";
private static UriMatcher uriMatcher;
private MyDatabaseHelper dbHelper;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(AUTHORITY, "book", BOOK_DIR);
uriMatcher.addURI(AUTHORITY, "book/#", BOOK_ITEM);
uriMatcher.addURI(AUTHORITY, "category", CATEGORY_DIR);
uriMatcher.addURI(AUTHORITY, "category/#", CATEGORY_ITEM);
}
//创建内容提供器
@Override
public boolean onCreate() {
dbHelper = new MyDatabaseHelper(getContext(), "BookStore.db", null, 2);
return true; //true表示创建成果
}
// 查询数据
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
SQLiteDatabase db = dbHelper.getReadableDatabase();
Cursor cursor = null;
//根据传入的Uri参数来判断访问哪张表
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
cursor = db.query("Book", projection, selection, selectionArgs, null, null, sortOrder);
break;
case BOOK_ITEM:
//getPathSegments()将内容URI权限之后的部分以"/“符号进行分割并存入字符串列表，0位置存放 路径，第1个位置存放id。
String bookId = uri.getPathSegments().get(1);
cursor = db.query("Book", projection, "id = ?", new String[] { bookId }, null, null, sortOrder);
break;
case CATEGORY_DIR:
cursor = db.query("Category", projection, selection, selectionArgs, null, null, sortOrder);
break;
case CATEGORY_ITEM:
String categoryId = uri.getPathSegments().get(1);
cursor = db.query("Category", projection, "id = ?", new String[] { categoryId }, null, null, sortOrder);
break;
default:
break;
}
return cursor;
}
// 添加数据
@Override
public Uri insert(Uri uri, ContentValues values) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
Uri uriReturn = null;
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
case BOOK_ITEM:
long newBookId = db.insert("Book", null, values);
//调用Uri.parse()方法将一个内容URI解析为Uri对象，该对象已新增数据的id结尾
uriReturn = Uri.parse("content://" + AUTHORITY + "/book/" + newBookId);
break;
case CATEGORY_DIR:
case CATEGORY_ITEM:
long newCategoryId = db.insert("Category", null, values);
uriReturn = Uri.parse("content://" + AUTHORITY + "/category/" + newCategoryId);
break;
default:
break;
}
return uriReturn;
}
// 更新数据
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
//受影响的行数作为返回值
int updatedRows = 0;
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
updatedRows = db.update("Book", values, selection, selectionArgs);
break;
case BOOK_ITEM:
String bookId = uri.getPathSegments().get(1);
updatedRows = db.update("Book", values, "id = ?", new String[] { bookId });
break;
case CATEGORY_DIR:
updatedRows = db.update("Category", values, selection, selectionArgs);
break;
case CATEGORY_ITEM:
String categoryId = uri.getPathSegments().get(1);
updatedRows = db.update("Category", values, "id = ?", new String[] { categoryId });
break;
default:
break;
}
return updatedRows;
}
// 删除数据
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
SQLiteDatabase db = dbHelper.getWritableDatabase();
//被删除的行数作为返回值
int deletedRows = 0;
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
deletedRows = db.delete("Book", selection, selectionArgs);
break;
case BOOK_ITEM:
String bookId = uri.getPathSegments().get(1);
deletedRows = db.delete("Book", "id = ?", new String[] { bookId });
break;
case CATEGORY_DIR:
deletedRows = db.delete("Category", selection, selectionArgs);
break;
case CATEGORY_ITEM:
String categoryId = uri.getPathSegments().get(1);
deletedRows = db.delete("Category", "id = ?", new String[] { categoryId });
break;
default:
break;
}
return deletedRows;
}
@Override
public String getType(Uri uri) {
switch (uriMatcher.match(uri)) {
case BOOK_DIR:
return "vnd.android.cursor.dir/vnd.com.example.databasetest. provider.book";
case BOOK_ITEM:
return "vnd.android.cursor.item/vnd.com.example.databasetest. provider.book";
case CATEGORY_DIR:
return "vnd.android.cursor.dir/vnd.com.example.databasetest. provider.category";
case CATEGORY_ITEM:
return "vnd.android.cursor.item/vnd.com.example.databasetest. provider.category";
}
return null;
}
}
2.在AndroidManifest.xml中注册内容提供器
注册这一步自动完成
<provider
android:name=".DatabaseProvider"
android:authorities="com.example.databasetest.provider"
android:enabled="true"
android:exported="true"></provider>
3.运行该项目，将该程序重新装在模拟器上
创建新项目ProviderTest
通过该程序去访问DatabaseTest中的数据
1. 编写布局文件
修改activity_main.xml，创建添加、更新、删除、查询按钮。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<Button
android:id="@+id/add_database"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Add database"/>
<Button
android:id="@+id/updata_database"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Updata database"/>
<Button
android:id="@+id/delet_database"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Delet_database"/>
<Button
android:id="@+id/query_database"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Query database"/>
</LinearLayout>
2. 访问DatabaseTest中的数据
修改MainActivity中的代码
package com.example.providertest;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
private String newId;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// 添加数据
Button addData = (Button) findViewById(R.id.add_database);
addData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//将内容URI解析为Uri对象
Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
//将要添加的数据存放在ContentValues对象中
ContentValues values = new ContentValues();
values.put("name", "A Clash of Kings");
values.put("author", "George Martin");
values.put("pages", 1040);
values.put("price", 55.55);
//调用insert方法执行添加操作
Uri newUri = getContentResolver().insert(uri, values);
//取出新增数据的id
newId = newUri.getPathSegments().get(1);
}
});
// 查询数据
Button queryData = (Button) findViewById(R.id.query_database);
queryData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
Cursor cursor = getContentResolver().query(uri, null, null, null, null);
if (cursor != null) {
while (cursor.moveToNext()) {
String name = cursor.getString(cursor. getColumnIndex("name"));
String author = cursor.getString(cursor. getColumnIndex("author"));
int pages = cursor.getInt(cursor.getColumnIndex ("pages"));
double price = cursor.getDouble(cursor. getColumnIndex("price"));
Log.d("MainActivity", "book name is " + name);
Log.d("MainActivity", "book author is " + author);
Log.d("MainActivity", "book pages is " + pages);
Log.d("MainActivity", "book price is " + price);
}
cursor.close();
}
}
});
// 更新数据
Button updateData = (Button) findViewById(R.id.updata_database);
updateData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//使用到了刚刚保存的新数据的id
Uri uri = Uri.parse("content://com.example.databasetest.provider/book/" + newId);
ContentValues values = new ContentValues();
values.put("name", "A Storm of Swords");
values.put("pages", 1216);
values.put("price", 24.05);
getContentResolver().update(uri, values, null, null);
}
});
//删除数据
Button deleteData = (Button) findViewById(R.id.delet_database);
deleteData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Uri uri = Uri.parse("content://com.example.databasetest.provider/book/" + newId);
getContentResolver().delete(uri, null, null);
}
});
}
}
3. 运行ProviderTest
点击ADD DATABASE按钮添加数据，再点击QUERY DATABASE查询数据，打印日志如图
点击UPDATE DATABASE按钮更新数据，再点击查询按钮，打印日志如图
点击DELET DATABASE按钮删除数据，再点击查询按钮，什么也不打印，因为数据已经被全部删掉啦！！！