【达内课程】ContentProvider（上）

增加功能实现

在联系人项目的基础上做如下修改：

增加PersonProvider

public class PersonProvider extends ContentProvider {
    @Override
    public boolean onCreate() {
        return false;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] strings, @Nullable String s, @Nullable String[] strings1, @Nullable String s1) {
        return null;
    }

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

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues contentValues) {
        DBOpenHelper dbOpenHelper = new DBOpenHelper(getContext());
        SQLiteDatabase db = dbOpenHelper.getWritableDatabase();

        String nullColumnHack = "_id";
        long id = db.insert("users",nullColumnHack,contentValues);

        //释放资源
        db.close();
        db = null;

        return null;
    }

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

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues contentValues, @Nullable String s, @Nullable String[] strings) {
        return 0;
    }
}

AndroidManifest

 <provider
     android:authorities="hello_world"
     android:name=".provider.PersonProvider"
     android:exported="true"/>

运行程序，让PersonProvider运行在模拟机上，我们顺便看一下数据有哪些

然后新建一个项目MyApplication2

MainActivity

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //测试增加数据
        testInsert();
    }

    private void testInsert() {
        //准备ContentResolver
        ContentResolver cr = getContentResolver();
        //相当于网址
        Uri uri = Uri.parse("content://hello_world");
        //向数据库中增加的数据的值
        ContentValues values = new ContentValues();
        values.put("_name","Susan");
        values.put("_age",44);
        values.put("_phone","14444444444");
        values.put("_email","[email protected]");
        //执行增加
        cr.insert(uri,values);
    }
}

运行程序，然后再打开第一个项目看下数据

已经增加成功了

查询数据的功能实现

如下：
PersonProvider

@Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] strings, @Nullable String s, @Nullable String[] strings1, @Nullable String s1) {
        //声明返回值
        List<Person> persons = new ArrayList<Person>();
        //获取SQLiteDatabase对象
        DBOpenHelper dbOpenHelper = new DBOpenHelper(getContext());
        SQLiteDatabase db = dbOpenHelper.getWritableDatabase();

        //执行业务：查询数据
        String table = "users";
        Cursor c = db.query("users", strings, s, strings1, null, null, s1);

        return c;
    }

第二个项目中的MainActivity

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //测试增加数据
        //testInsert();
        //测试查询数据
        testQuery();
    }

    private void testQuery() {
        ContentResolver cr = getContentResolver();
        Uri uri = Uri.parse("content://hello_world");
        //执行查询
        Cursor c = cr.query(uri, null, null, null, null);
        for(c.moveToFirst();!c.isAfterLast();c.moveToNext()){
            int id = c.getInt(c.getColumnIndex("_id"));
            String name = c.getString(c.getColumnIndex("_name"));
            int age = c.getInt(c.getColumnIndex("_age"));
            String phone = c.getString(c.getColumnIndex("_phone"));
            String email = c.getString(c.getColumnIndex("_email"));
            Log.d("CONTENT_PROVIDER","id:"+id+";name:"+name+";age:"+age+":phone:"+phone+";email:"+email);
        }
    }

    ......
}

运行第二个项目，查看日志如下

我们打开Device File Explorer，我们会发现有很多包含providers的文件夹，这些是安卓内置的使用ContentProvider共享数据的程序

打开com.android.providers.media中databases，导出internal.db

我们打开audio表，可以看到歌曲相关信息

同样打开external.db，可以看到我们音乐播放器3项目中的歌曲

改进音乐播放器3

新增MediaStoreMusicDao

public class MediaStoreMusicDao implements IDao<Music> {
    private Context content;

    public MediaStoreMusicDao(Context content) {
        this.content = content;
    }

    @Override
    public List<Music> getData() {
        //声明返回值
        List<Music> musics = new ArrayList<>();
        //准备ContentResolver
        ContentResolver cr = content.getContentResolver();
        //准备Uri
        Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
        //读数据，获取Cursor对象
        String[] projection = {
                "_id",//0
                "_data",//1->path
                "title",//2
                "duration",//3
                "album",//4
                "artist",//5
                "album_artist"//
        };//读取的字段
        String selection = null;
        String[] selectionArgs = null;
        String sortOrder = null;
        Cursor c = cr.query(uri,projection,selection,selectionArgs,sortOrder);
        //遍历Cursor，向返回值中添加数据
        for(c.moveToFirst();!c.isAfterLast();c.moveToNext()){
            Music music = new Music();
            music.setId(c.getLong(0));
            music.setPath(c.getString(1));
            music.setTitle(c.getString(2));
            music.setDuration(c.getInt(3));
            music.setAlbum(c.getString(4));
            music.setArtist(c.getString(5));
            music.setAlbumArtist(c.getString(6));
            musics.add(music);
        }

        //释放资源
        c.close();
        c = null;

        return musics;
    }
}

修改MusicDaoFactory

public class MusicDaoFactory {
    //如果是单例，就用getInstance();
    public static IDao<Music> newInstance(Context context){
        return new MediaStoreMusicDao(context);
    }
}

修改Music类，我们要存储更多的数据

public class Music {
    private long id;
    private String title;
    private String path;
    private int duration;
    private String album;
    private String artist;
    private String albumArtist;

    public long getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getPath() {
        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }

    public int getDuration() {
        return duration;
    }

    public void setDuration(int duration) {
        this.duration = duration;
    }

    public String getAlbum() {
        return album;
    }

    public void setAlbum(String album) {
        this.album = album;
    }

    public String getArtist() {
        return artist;
    }

    public void setArtist(String artist) {
        this.artist = artist;
    }

    public String getAlbumArtist() {
        return albumArtist;
    }

    public void setAlbumArtist(String albumArtist) {
        this.albumArtist = albumArtist;
    }
}

我们之前的音乐播放器只显示了标题和路径，我们可以调整界面，显示更多的内容了

item_music

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="10dp">

    <TextView
        android:id="@+id/tv_music_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:maxLines="1"
        android:text="title"
        android:textColor="#222222"
        android:textSize="15dp"
        />
    <TextView
        android:id="@+id/tv_music_duration"
        android:layout_width="50dp"
        android:layout_height="wrap_content"
        android:maxLines="1"
        android:text="00:00"
        android:textColor="#222222"
        android:textSize="15dp"
        android:layout_alignParentRight="true"
        android:layout_marginLeft="10dp"
        />

    <TextView
        android:id="@+id/tv_music_album"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:maxLines="1"
        android:layout_below="@+id/tv_music_title"
        android:text="path......"
        android:textColor="#999999"
        android:textSize="15dp"
        />

    <TextView
        android:id="@+id/tv_music_artist"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:maxLines="1"
        android:layout_below="@+id/tv_music_title"
        android:text="path......"
        android:textColor="#999999"
        android:textSize="15dp"
        android:layout_toRightOf="@+id/tv_music_album"
        android:layout_marginLeft="10dp"
        />
</RelativeLayout>

修改MusicAdapter

public class MusicAdapter extends BaseAdapter<Music> {
    public MusicAdapter(Context context, List data) {
        super(context, data);
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        Music music = getData().get(i);

        ViewHolder holder;

        if(view == null){
            view = getInflater().inflate(R.layout.item_music,null);
            holder = new ViewHolder();
            holder.title = view.findViewById(R.id.tv_music_title);
            holder.duration = view.findViewById(R.id.tv_music_duration);
            holder.album = view.findViewById(R.id.tv_music_album);
            holder.artist = view.findViewById(R.id.tv_music_artist);
            view.setTag(holder);
        }else{
            holder = (ViewHolder) view.getTag();
        }

        holder.title.setText(music.getTitle());
        holder.duration.setText(CommonUtils.getFormattedTime(music.getDuration()));
        holder.album.setText(music.getAlbum());
        holder.artist.setText(music.getArtist());

        return view;
    }

    class ViewHolder{
        TextView title;
        TextView duration;
        TextView album;
        TextView artist;
    }
}

同时之前通过MediaPlayer获得时长的代码

player.getDuration()

可以全部替换成

musics.get(currentMusicIndex).getDuration()

可以通过数据库读取了

因为自带的模拟器对中文的支持不是很好，如果出现???是无解题，最终显示效果可以参看模拟器自带的Music应用显示效果