contentProvider 和database 和sqllite

frameworks\base\core\java\android\database\sqlite\SQLiteOpenHelper.java

数据库的创建与版本更新管理辅助类，这个辅助类使得对ContentProvider控制更容易，这个辅助类创建的时候并不会创建数据库或者升级数据库，而只有在使用数据库的时候才会第一次创建数据库或者升级数据库，从而延迟数据库创建与升级，避免在应用启动的时候阻塞应用，而直接使用contentprovider 就会导致创建、升级数据库应用启动慢。

 

public abstract class SQLiteOpenHelper {

       private SQLiteDatabase mDatabase;   //

}

nchronized void	close() Close any open database object.
synchronizedSQLiteDatabase	getReadableDatabase() Create and/or open a database.
synchronizedSQLiteDatabase	getWritableDatabase() Create and/or open a database that will be used for reading and writing.
abstract void	onCreate(SQLiteDatabase db)(在派生类中必须被重写) Called when the database is created for the first time.
void	onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) Called when the database needs to be downgraded.
void	onOpen(SQLiteDatabase db) Called when the database has been opened.
abstract void	onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)(在派生类中必须被重写) Called when the database needs to be upgraded.

 

它提供了两个重要的方法，分别是

onCreate(SQLiteDatabase db)：用户初次使用软件时生成数据库，一旦数据库存在则不会调用此方法。函数是在第一次创建数据库的时候执行的，仅仅生成DataBaseHelper对象（SQLiteOpenHelper类型）的时候是不会调用该函数的，而只有当调用DataBaseHelper对象的getReadableDataBase时或者是调用了getWritableDataBase时，如果是第一次创建数据库，那么就一定会调用onCreate()函数。

onUpgrade(SQLiteDatabase db，int oldVersion，int vewVersion)：用于升级软件时更新数据库表结构，如增加表、列字段等操作。

提示一下，在软件升级前，最好对原有数据进行备份，在新表建好后把数据导入新表中。

 实现了这两个方法，就可以用它的getWritableDatabase()和getReadableDatabase()来获得数据库（SQLiteDatabase 对象）。

强调下：当第一次创建数据库时，当实现DataBaseHelper对象的getReadableDataBase时或者是调用了getWritableDataBase时，系统自动调用oncreater(）方法（当然程序中也可以调用）；

如果用户需要升级数据库表结构，需要主动调用onUpgrade(SQLiteDatabase db，int oldVersion，int vewVersion),传入一个新的版本的号。

继承该类并覆盖onCreate,onUpgrade,onOpen(可选)。我们可以创建或打开数据库，并对其进行升级。通过getReadableDataBase和getWritableDataBase获取SQliteDataBase实例。通过close关闭数据库。

 

Sdk\sources\android-28\android\content\ContentProvider.java

public abstract boolean onCreate();

这里在应用启动时会在主线程中调用，创建数据库。

 

在使用时，可以在onCreate()中初始化 DatabaseHelper，在应用中通过

getContentResolver().query 。。。。  调用MyContentProvider 中方法，从而达到不让应用阻塞

@Override
public boolean onCreate() {
    mDatabaseHelper = new MyDatabaseHelper(getContext());
    return true;
}

 

MainActivity.java

package com.wuyue.testcontentprovider;

import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
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;
import android.widget.Toast;

import java.util.Random;

public class MainActivity extends Activity {

    static final String TAG = "CONTENTPROVIDER";
    ContentResolver mContentResolver;
    Uri mUri = Uri.parse("content://org.wuyue.statistic.list/");
    MyContentProvider mContentProvider;


    SQLiteDatabase mSQLdb;
    String mDbFilePath;
    static final String TABLE_NAME = "new_infs";
    static final String TABLE_CREATE = "create table " + TABLE_NAME + "(_id integer"
            + " primary key autoincrement,"
            + " news_title varchar(50),"
            + " news_content varchar(255))";
    Button mButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //create db
//        mDbFilePath = this.getFilesDir().toString() + "/wuyue.db";
//        Log.d(TAG,"database path:" + mDbFilePath);
//        mSQLdb = SQLiteDatabase.openOrCreateDatabase(mDbFilePath,null);
//        try {
//            mSQLdb.execSQL(TABLE_CREATE);
//        }catch (SQLException e){
//            Log.d(TAG,"" + e);
//        }
        //mContentProvider = new MyContentProvider();


        mButton = (Button)findViewById(R.id.btn);
        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Random random = new Random();
                int r = random.nextInt();
                ContentValues values = new ContentValues();
                values.put("news_title","abc" + r);
                values.put("news_content","abc");
                //mSQLdb.insert(TABLE_NAME,null,values);

                Uri uri = Uri.parse("content://org.wuyue.statistic.list/" + TABLE_NAME);
                //mContentProvider.insert(uri,values);
                getContentResolver().insert(uri,values);

                String[] cols = {"_id","news_title","news_content"};
               // Cursor c = mSQLdb.query(TABLE_NAME,cols,null,null,null,null,null);

                //Cursor c = mContentProvider.query(uri,null,null,null,null,null);
                Cursor c = getContentResolver().query(uri,null,null,null,null);
                if(c.getCount() > 0){
                    while(c.moveToNext()){
                        String id = c.getString(0);
                        String title = c.getString(1);
                        String content = c.getString(2);
                        Log.d(TAG,"id = " + id + "  title= " + title + "  content= " + content);
                    }
                }
            }
        });
        mContentResolver = getContentResolver();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if(mSQLdb != null && mSQLdb.isOpen()){
            mSQLdb.close();
        }
    }

    public void insert(View source){
        ContentValues cv = new ContentValues();
        cv.put("name","abc");
        Uri newUri = mContentResolver.insert(mUri,cv);
        Toast.makeText(this,"insert" + newUri,Toast.LENGTH_LONG).show();
    }

    public void query(View source){
        Cursor c = mContentResolver.query(mUri,null,"query_where",null,null);
        Toast.makeText(this,"query" + c ,Toast.LENGTH_LONG).show();
    }
}

MyContentProvider.java

package com.wuyue.testcontentprovider;

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;
import android.os.Bundle;
import android.os.CancellationSignal;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

import java.util.Random;

public class MyContentProvider extends ContentProvider{
    private final static int NEW_INFS = 0, BOOK = 1;
    private final static String authority = "org.wuyue.statistic.list";
    private static UriMatcher mMatcher = new UriMatcher(UriMatcher.NO_MATCH);

    private MyDatabaseHelper mDatabaseHelper;

    static {
        mMatcher.addURI(authority, "new_infs", NEW_INFS);//TABLE new_infs
        mMatcher.addURI(authority, "book", BOOK);
    }

    public MyContentProvider() {
        super();
    }

    private String getTableName(Uri uri) {
        int code = mMatcher.match(uri);
        switch (code) {
            case NEW_INFS:
                return "new_infs";
            case BOOK:
                return "book";
            default:
                return null;
        }
    }

    @Override
    public boolean onCreate() {
        mDatabaseHelper = new MyDatabaseHelper(getContext());
        return true;
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        String table = getTableName(uri);
        if (table != null) {
            mDatabaseHelper.insert(table/*mDatabaseHelper.getDatabaseName()*/,null,values);
            return uri;
        }
        return null;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder, @Nullable CancellationSignal cancellationSignal) {
        String table = getTableName(uri);
        if (table != null) {
            String[] cols = {"_id", "news_title", "news_content"};
            return mDatabaseHelper.query(/*mDatabaseHelper.getDatabaseName()*/table,cols,null,null,null,null,null);
        }
        return super.query(uri, projection, selection, selectionArgs, sortOrder, cancellationSignal);
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable Bundle queryArgs, @Nullable CancellationSignal cancellationSignal) {
        return super.query(uri, projection, queryArgs, cancellationSignal);
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        return null;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        return null;
    }
}

MyDatabaseHelper.java

package com.wuyue.testcontentprovider;

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.Random;

public class MyDatabaseHelper extends SQLiteOpenHelper{
    static final String TABLE_NAME = "new_infs";
    static final String TABLE_CREATE = "create table " + TABLE_NAME + "(_id integer"
            + " primary key autoincrement,"
            + " news_title varchar(50),"
            + " news_content varchar(255))";

    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context.getApplicationContext(), name, factory, version);
    }

    public MyDatabaseHelper(Context context){
        super(context.getApplicationContext(), TABLE_NAME, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(TABLE_CREATE);
    }

    @Override
    public void onOpen(SQLiteDatabase db) {
        super.onOpen(db);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        if(newVersion > oldVersion){
            db.execSQL("delete from " + TABLE_NAME);
        }
    }

    @Override
    public SQLiteDatabase getWritableDatabase() {
        return super.getWritableDatabase();
    }

    @Override
    public SQLiteDatabase getReadableDatabase() {
        return super.getReadableDatabase();
    }

    public Cursor query(String table, String[] columns, String selection,
                 String[] selectionArgs, String groupBy, String having,
                 String orderBy){
        Cursor c = getReadableDatabase().query(table, columns, selection,selectionArgs,groupBy,having,orderBy);
        return c;
    }

    public long insert(String table, String nullColumnHack, ContentValues values){
        return getWritableDatabase().insert(table,nullColumnHack,values);
    }
}

AndroidManifest.xml