第七章--内容提供器

1.内容提供器简介

• Content Provider是用于不同应用程序之间实现数据共享的功能，它提供了一套完整的机制，允许一个程序访问另一个程序中的数据，同时保证数据的安全性。

2.权限处理

• android6.0以后对一些危险权限需要请求用户允许，弹出授权对话框之类的

   if (ContextCompat.checkSelfPermission(LoginActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE)!= 
                PackageManager.PERMISSION_GRANTED){
                ActivityCompat.requestPermissions(LoginActivity.this,
                    new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},1);
        }

  @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode){
            case 1:
                Toast.makeText(LoginActivity.this,"premission  failure",Toast.LENGTH_SHORT).show();
                break;
        }
    }

3. 读取系统联系人

• 注意添加权限

    private void readContacts() {
        Cursor  cursor=null;
        try {
            cursor=getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,null,null,null,null);
            if (cursor!=null){
                while (cursor.moveToNext()){
                    String  name=cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                    String  phonenumber=cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
                    
                    //listdatas.add(name"/n"+phonenumber);
                }
                //adapter.notifyDataSetChanged();
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
               if (cursor!=null){
                   cursor.close();
               }
        }
        
    }

4.创建自己的内容提供器实现跨程序数据共享

• provider 在清单文件中注册

public class DatabaseProvider extends ContentProvider {

    public static final int BOOK_DIR = 0;

    public static final int BOOK_ITEM = 1;

    public static final int CATEGORY_DIR = 2;

    public static final int CATEGORY_ITEM = 3;

    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);
    }

    @Override
    public boolean onCreate() {
        dbHelper = new MyDatabaseHelper(getContext(), "BookStore.db", null, 2);
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        // 查询数据
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        Cursor cursor = null;
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
                cursor = db.query("Book", projection, selection, selectionArgs, null, null, sortOrder);
                break;
            case BOOK_ITEM:
                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;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // 添加数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        Uri uriReturn = null;
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
            case BOOK_ITEM:
                long newBookId = db.insert("Book", null, values);
                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;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        // 更新数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        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;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // 删除数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        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;
    }

}