Android ContentProvider简介

1. 前言

ContentProvider为存储和获取数据提供统一的接口，可以在不同的应用程序之间共享数据。

2. 读取通讯录

常通过ContentProvider来读取通讯录的信息。

Cursor cursor = getContentResolver().query(ContactsContract.Contacts.CONTENT_URI,
            null, null, null, null);

while (cursor.moveToNext()) {
    int id = cursor.getInt(cursor.getColumnIndex(
            ContactsContract.Contacts._ID));
    String name = cursor.getString(cursor.getColumnIndex(
            ContactsContract.Contacts.DISPLAY_NAME));
}
cursor.close();

需要在AndroidManifest.xml中添加权限。

<uses-permission android:name="android.permission.READ_CONTACTS" />

2. 自定义ContentProvider

自定义ContentProvider利用数据库提供了数据，并对数据进行查询和修改操作。

用户数据库

利用SQLiteOpenHelper创建，数据库包含ID、姓名、地址和年龄。

public class PeopleSQLiteOpenHelper extends SQLiteOpenHelper {
    public final static String LOGTAG = "PeopleSQLiteOpenHelper";

    public final static String DB_NAME = "people.db";
    public final static String TABLE_NAME = "people";
    public final static int VERSION = 1;

    public final static String COL_ID   = "_id";
    public final static String COL_NAME = "name";
    public final static String COL_ADDR = "addr";
    public final static String COL_AGE  = "age";

    public final static String TABLE_CREATE =
            "create table if not exists " + TABLE_NAME + "("
                    + COL_ID + " integer primary key autoincrement not null,"
                    + COL_NAME + " text not null, "
                    + COL_ADDR + " text not null, "
                    + COL_AGE + " integer "
                    + ")";

    public PeopleSQLiteOpenHelper(Context context) {
        super(context, DB_NAME, null, VERSION);
    }

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

}

自定义ContentProvider

在自定义ContentProvider之前，为了安全需要添加自定义权限。

<!-- 定义读取权限 -->
<permission android:name="com.blog.demo.READ_PEOPLE" />
<!-- 定义修改权限 -->
<permission android:name="com.blog.demo.WRITE_PEOPLE" />

同时也要添加ContentProvider声明，指定读取和写入权限。

<!-- authorities是标识，访问时需要 -->
<!-- 设置export为true，对其他apk开放 -->
<provider
    android:authorities="com.blog.demo.people"
    android:name=".component.cont.PeopleContentProvider"
    android:readPermission="com.blog.demo.READ_PEOPLE"
    android:writePermission="com.blog.demo.WRITE_PEOPLE" />

自定义PeopleContentProvider继承ContentProvider，实现了查询、插入、删除和修改四类操作。
定义 people 和 people/# 两种不同uri请求，并利用UriMatcher来解析。people 代表所有用户，people/# 代表某个用户。

public class PeopleContentProvider extends ContentProvider {
    private static final String AUTHORITY   = "com.blog.demo.people";
    private static final String TABLE_NAME  = PeopleSQLiteOpenHelper.TABLE_NAME;

    private static final int PEOPLE      = 1;
    private static final int PEOPLE_ID   = 2;

    private static final UriMatcher uriMatcher;
    static {
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI(AUTHORITY, "people", PEOPLE);
        uriMatcher.addURI(AUTHORITY, "people/#", PEOPLE_ID);
    }

    private PeopleSQLiteOpenHelper helper;

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        switch(uriMatcher.match(uri)) {
            case PEOPLE: // 集合类型 vnd.android.cursor.dir
                return "vnd.android.cursor.dir/com.blog.demo.people";
            case PEOPLE_ID: // 非集合类型 vnd.android.cursor.item
                return "vnd.android.cursor.item/com.blog.demo.people";
            default:
                throw new IllegalArgumentException("Unsupported URI: " + uri);
        }
    }

    @Override
    public boolean onCreate() {
        helper = new PeopleSQLiteOpenHelper(getContext());
        return true;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection,
                        @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        if (uriMatcher.match(uri) == PEOPLE) {
            // 查询所有people数据
            return helper.getReadableDatabase().query(TABLE_NAME, projection,
                    selection, selectionArgs, null, null, sortOrder);   
        } else if (uriMatcher.match(uri) == PEOPLE_ID) {
            // 查询所有指定id的people数据
            String id = uri.getPathSegments().get(1);
            return helper.getReadableDatabase().query(TABLE_NAME, projection,
                    PeopleSQLiteOpenHelper.COL_ID +"=?", new String[]{id},
                    null, null, sortOrder);
        }
        throw new IllegalArgumentException("Unsupported URI: " + uri);
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        if (uriMatcher.match(uri) == PEOPLE) {
            SQLiteDatabase db = helper.getWritableDatabase();
            try {
                db.beginTransaction();
                long id = db.insert(TABLE_NAME, null, values);
                if (id > 0) {
                    db.setTransactionSuccessful();
                    return ContentUris.withAppendedId(uri, id);
                }
            } finally {
                db.endTransaction();
            }
        }
        throw new IllegalArgumentException("Unsupported URI: " + uri);
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        if (uriMatcher.match(uri) == PEOPLE_ID) {
            String id = uri.getPathSegments().get(1);

            SQLiteDatabase db = helper.getWritableDatabase();
            try {
                db.beginTransaction();
                int result = db.delete(TABLE_NAME,
                        PeopleSQLiteOpenHelper.COL_ID +"=?", new String[]{id});
                db.setTransactionSuccessful();
                return result;
            } finally {
                db.endTransaction();
            }
        }
        throw new IllegalArgumentException("Unsupported URI: " + uri);
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection,
                      @Nullable String[] selectionArgs) {
        if (uriMatcher.match(uri) == PEOPLE_ID) {
            String id = uri.getPathSegments().get(1);

            SQLiteDatabase db = helper.getWritableDatabase();
            try {
                db.beginTransaction();
                int result = db.update(TABLE_NAME, values,
                        PeopleSQLiteOpenHelper.COL_ID +"=?", new String[]{id});
                db.setTransactionSuccessful();
                return result;
            } finally {
                db.endTransaction();
            }
        }
        throw new IllegalArgumentException("Unsupported URI: " + uri);  
    }

}

3. 读取用户数据

需要添加读取权限。

<uses-permission android:name="com.blog.demo.READ_PEOPLE"/>
<uses-permission android:name="com.blog.demo.WRITE_PEOPLE"/>

查询操作，查询所有用户信息和根据ID查询某个用户信息。

private void query() {
    List<People> list = new ArrayList<>();

    Cursor cursor = getContentResolver().query(PeopleConstant.CONTENT_URI,
            null, null, null, null);
    if (cursor != null) {
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex(PeopleColumns.ID));
            String name = cursor.getString(cursor.getColumnIndex(PeopleColumns.NAME));
            String addr = cursor.getString(cursor.getColumnIndex(PeopleColumns.ADDR));
            int age = cursor.getInt(cursor.getColumnIndex(PeopleColumns.AGE));
            list.add(new People(id, name, addr, age));
        }
        cursor.close();
    }

}

private void query(int id) {
    Cursor cursor = getContentResolver().query(
            ContentUris.withAppendedId(PeopleConstant.CONTENT_URI, id),
            null, null, null, null);
    if (cursor != null) {
        People people = null;
        if (cursor.moveToNext()) {
            int rid = cursor.getInt(cursor.getColumnIndex(PeopleColumns.ID));
            String name = cursor.getString(cursor.getColumnIndex(PeopleColumns.NAME));
            String addr = cursor.getString(cursor.getColumnIndex(PeopleColumns.ADDR));
            int age = cursor.getInt(cursor.getColumnIndex(PeopleColumns.AGE));
            people = new People(rid, name, addr, age);
        }
        cursor.close();
    }
}

添加、修改和删除操作。

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private void insert(String name, String addr, int age) {
    ContentValues insertValues = new ContentValues();
    insertValues.put(PeopleColumns.NAME, name);
    insertValues.put(PeopleColumns.ADDR, addr);
    insertValues.put(PeopleColumns.AGE, age);

    getContentResolver().insert(PeopleConstant.CONTENT_URI, insertValues);
}

private void update(int id, String name, String addr, int age) {
    ContentValues updateValues = new ContentValues();
    updateValues.put(PeopleColumns.NAME, name);
    updateValues.put(PeopleColumns.ADDR, addr);
    updateValues.put(PeopleColumns.AGE, age);
    getContentResolver().update(ContentUris.withAppendedId(
            PeopleConstant.CONTENT_URI, id),
            updateValues, null, null);
}

private void delete(int id) {
    getContentResolver().delete(ContentUris.withAppendedId(
            PeopleConstant.CONTENT_URI, id), null, null);    
}

辅助类PeopleConstant。

public class PeopleConstant {

    public final static Uri CONTENT_URI =
            Uri.parse("content://com.blog.demo.people/people");

    public final static class PeopleColumns {
        public final static String ID   = "_id";
        public final static String NAME = "name";
        public final static String ADDR = "addr";
        public final static String AGE  = "age";
    }

}