安卓学习日记——Loader

例子展示
在这里插入图片描述
代码块
DatabaseAdapter

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 DatabaseAdapter {

    private DatabaseHelper dbHelper;

    public DatabaseAdapter(Context context){
        dbHelper=new DatabaseHelper(context);
    }

    public void save(Person person){
        SQLiteDatabase db=dbHelper.getWritableDatabase();
        ContentValues values=new ContentValues();
        values.put(PersonMetadata.Person.NAME,person.getName());
        values.put(PersonMetadata.Person.AGE,person.getAge());
        db.insert(PersonMetadata.Person.TABLE_NAME,null,values);
        db.close();
    }

    public void delete(int id){
        SQLiteDatabase db=dbHelper.getWritableDatabase();
        db.delete(PersonMetadata.Person.TABLE_NAME, PersonMetadata.Person._ID+"=?",new String[]{String.valueOf(id)});
        db.close();
    }

    public void update(Person person){
        SQLiteDatabase db=dbHelper.getWritableDatabase();
        ContentValues values=new ContentValues();
        values.put(PersonMetadata.Person.NAME,person.getName());
        values.put(PersonMetadata.Person.AGE,person.getAge());
        String where=PersonMetadata.Person._ID+"=?";
        String[] args={String.valueOf(person.getId())};
        db.update(PersonMetadata.Person.TABLE_NAME,values,where,args);
        db.close();
    }
    public ArrayList<Person> findAll(){
        SQLiteDatabase db= dbHelper.getReadableDatabase();
        Cursor c= db.query(PersonMetadata.Person.TABLE_NAME,null,null,null,null,null,null);
        ArrayList<Person> list=new ArrayList<>();
        Person person=null;
        while (c.moveToNext()){
            person=new Person();
            person.setId(c.getInt(c.getColumnIndex(PersonMetadata.Person._ID)));
            person.setName(c.getString(c.getColumnIndex(PersonMetadata.Person.NAME)));
            person.setAge(c.getInt(c.getColumnIndex(PersonMetadata.Person.AGE)));
            list.add(person);
        }
        c.close();
        db.close();
        return list;
    }

    public Cursor list(){
        SQLiteDatabase db= dbHelper.getReadableDatabase();
        Cursor c= db.query(PersonMetadata.Person.TABLE_NAME,null,null,null,null,null,null);
        return c;
    }


    public Person findById(int id){
        SQLiteDatabase db= dbHelper.getReadableDatabase();
        Cursor c= db.query(PersonMetadata.Person.TABLE_NAME,null,PersonMetadata.Person._ID+"=?",new String[]{String.valueOf(id)},null,null,null);
        Person person=null;
        if (c.moveToNext()){
            person=new Person();
            person.setId(c.getInt(c.getColumnIndex(PersonMetadata.Person._ID)));
            person.setName(c.getString(c.getColumnIndex(PersonMetadata.Person.NAME)));
            person.setAge(c.getInt(c.getColumnIndex(PersonMetadata.Person.AGE)));
        }
        c.close();
        db.close();
        return person;
    }

    public static class DatabaseHelper extends SQLiteOpenHelper{
        private static final String DB_NAME="cp.db";
        private static final int VERSION=1;
        private static final String CREATE_TABLE="CREATE TABLE person(_id integer primary key autoincrement,name text,age int)";
        private static final String DROP_TABLE="DROP TABLE IF EXISTS person";
        public DatabaseHelper(Context context) {
            super(context, DB_NAME, null, VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {

            db.execSQL(CREATE_TABLE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL(DROP_TABLE);
        db.execSQL(CREATE_TABLE);
        }
    }
}

HelloContentProvider

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;

/**
 * 自定义ContentProvider
 */
public class HelloContentProvider extends ContentProvider {
    private static final String authority="com.example.HelloContentProvider";
    //创建一个URI的匹配器,
    private static UriMatcher uriMatcher=new UriMatcher(UriMatcher.NO_MATCH);
    private static final int single_code=2;//返回单个记录的匹配码
    private static final int mutiple_code=1;//返回多个记录的匹配码
    //text/plain image/jpg
    private static final String SINGLE_TYPE="vnd.android.cursor.item/person";
    private static final String MUTIPLE_TYPE="vnd.android.cursor.dir/person";
    static {

        uriMatcher.addURI(authority,"person",mutiple_code);

        uriMatcher.addURI(authority,"person/#",single_code);
    }
private DatabaseAdapter.DatabaseHelper dbHelper;
    @Override
    public boolean onCreate() {
        dbHelper=new DatabaseAdapter.DatabaseHelper(getContext());
        return false;
    }


    @Override
    public Cursor query(Uri uri, String[] projection,String selection,String[] selectionArgs,String sortOrder) {
       switch (uriMatcher.match(uri)){
           case single_code:
               SQLiteDatabase db=dbHelper.getReadableDatabase();
               long id=ContentUris.parseId(uri);
               selection= PersonMetadata.Person._ID+"=?";
               selectionArgs=new String[]{String.valueOf(id)};
              return db.query(PersonMetadata.Person.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);
           case mutiple_code:
               db=dbHelper.getReadableDatabase();
               return db.query(PersonMetadata.Person.TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder);

       }
        return null;
    }


    @Override
    public String getType(Uri uri) {
        switch (uriMatcher.match(uri)){
            case single_code:
                return SINGLE_TYPE;
            case mutiple_code:
                return MUTIPLE_TYPE;
        }
        return null;
    }


    @Override
    public Uri insert(Uri uri,ContentValues values) {
        switch (uriMatcher.match(uri)){
            case mutiple_code:
                SQLiteDatabase db=dbHelper.getWritableDatabase();
               long id=db.insert(PersonMetadata.Person.TABLE_NAME,null,values);
                uri=ContentUris.withAppendedId(uri,id);
                db.close();
                break;

        }
        return uri;
    }

    @Override
    public int delete(Uri uri, String selection,  String[] selectionArgs) {
        switch (uriMatcher.match(uri)){

            case single_code:
                SQLiteDatabase db=dbHelper.getWritableDatabase();
                long id=ContentUris.parseId(uri);
                 selection= PersonMetadata.Person._ID+"=?";
                 selectionArgs=new String[]{String.valueOf(id)};
                int row=db.delete(PersonMetadata.Person.TABLE_NAME,selection,selectionArgs);
                db.close();
                return row;

            case mutiple_code:
                db=dbHelper.getWritableDatabase();
               row=db.delete(PersonMetadata.Person.TABLE_NAME,selection,selectionArgs);
                db.close();
                return row;
        }
        return 0;
    }

    @Override
    public int update( Uri uri, ContentValues values,  String selection, String[] selectionArgs) {
        switch (uriMatcher.match(uri)){

            case single_code:
                SQLiteDatabase db=dbHelper.getWritableDatabase();
                long id=ContentUris.parseId(uri);
                selection= PersonMetadata.Person._ID+"=?";
                selectionArgs=new String[]{String.valueOf(id)};
                int row=db.update(PersonMetadata.Person.TABLE_NAME,values,selection,selectionArgs);
                db.close();
                return row;

            case mutiple_code:
                db=dbHelper.getWritableDatabase();
                row=db.update(PersonMetadata.Person.TABLE_NAME,values,selection,selectionArgs);
                db.close();
                return row;
        }
        return 0;
    }
}

Person

public class Person {
    private int id;
    private String name;
    private int age;

    public Person(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public Person() {
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

PersonMetadata

import android.provider.BaseColumns;

public final class PersonMetadata {

    public static abstract class Person implements BaseColumns {
        public static final String TABLE_NAME="person";
        public static final String NAME="name";
        public static final String AGE="age";
    }
}

MainActivity

import android.database.Cursor;
import android.net.Uri;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.SimpleCursorAdapter;

public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {

    private DatabaseAdapter dbAdapter;
    SimpleCursorAdapter dataAdapter;
    CursorLoader loader;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbAdapter=new DatabaseAdapter(this);
        ListView lv=findViewById(R.id.listView);
        dataAdapter=new SimpleCursorAdapter(this,R.layout.list_item,
                dbAdapter.list(),
                new String[]{PersonMetadata.Person._ID, PersonMetadata.Person.NAME, PersonMetadata.Person.AGE},
                new int[]{R.id.textView_id,R.id.textView2_name,R.id.textView3_age},
                SimpleCursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);

        lv.setAdapter(dataAdapter);
        //初始化一个Loader(id,bundler参数,回调接口)
        getSupportLoaderManager().initLoader(0,null,this);
    }
    public void addClick(View v){
        dbAdapter.save(new Person("ck",18));
        //重启加载器
//        getSupportLoaderManager().restartLoader(0,null,this);
//        loader.commitContentChanged();api 18可用
        loader.onContentChanged();//内容发生变化，通知加载器
    }


    @NonNull
    @Override
    public Loader<Cursor> onCreateLoader(int i, @Nullable Bundle bundle) {
        System.out.println("onCreateLoader");
        Uri uri=Uri.parse("content://com.example.HelloContentProvider/person");
        //创建一个游标加载器(上下文，CP的URI，要查询的列数组，查询条件，查询条件的值，排序条件)
        loader=new CursorLoader(this,uri,null,null,null,null);
        return loader;
    }

    @Override
    public void onLoadFinished(@NonNull Loader<Cursor> loader, Cursor data) {
        System.out.println("onLoadFinished");
            dataAdapter.swapCursor(data);
    }

    @Override
    public void onLoaderReset(@NonNull Loader<Cursor> loader) {
        System.out.println("onLoaderReset");
        dataAdapter.swapCursor(null);
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:onClick="addClick"
        android:layout_marginStart="0dp"
        android:layout_marginTop="0dp"
        android:text="add" />

    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:id="@+id/listView"
        android:layout_marginStart="0dp"
        android:layout_marginTop="64dp" />
</RelativeLayout>

list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textView_id"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="TextView" />

    <TextView
        android:id="@+id/textView2_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="TextView" />

    <TextView
        android:id="@+id/textView3_age"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="TextView" />
</LinearLayout>

安卓学习日记——Loader

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