Question

我正在为我的应用开发自定义内容提供商。这是我使用Android应用程序的课程的一部分，所以请不要期望做到这一切的理由太过分了;-)这里的重点是让我了解CP。< / p>

我有一个previous post which goes on and on with this，但我想我已经设法简化了我的问题。所以，我正在使用＃34; gallery应用程序＆＃34;。由于我不知道手机上存储 thumbnail 图像的方式和位置，我决定只使用MediaStore.Images.Thumbnails来访问拇指，并在我的手机中显示它们网格视图。

然而，为了满足所述课程的要求，我将写一个＆＃34; PhotoProvider＆＃34;在DetailActivity中加载单张照片，全屏。此外，为了使这一点有意义，而不仅仅是MediaStore.Media.Images的包装器，我使用JPEG文件中的一些EXIF标签扩展该数据。

找到了great post here on StackOverflow，并继续纠缠课堂上提供的源代码，我提出了以下课程。也许你想看看，帮助我（指出我正确的方向）？

我支持的URI context://AUTH/photo/#，用于从缩略图中获取特定图片（给定IMAGE_ID）。此外，为了使它更有趣，我还希望能够将数据写入EXIF标记UserComment：context://AUTH/photo/#/comment/*（注释String是那里的最后一个参数）。那看起来合情合理吗？

有些问题：（已更新）

getType()令人困惑。同样，这是从应用课程借出的。返回图片时，我想类型应始终为image/jpeg（或者PNG）？

编辑：了解更多内容，我现在明白从insert()方法返回的URI是可选的，但是返回＆＃34;链接通常很有用＃34; （即URI）到新的（插入的）数据！对于我的情况，在更新EXIF标记后，我可以向已修改的照片返回null或URI：context://AUTH/photo/7271（其中7271模仿PHOTO_ID）。

以下是我的（未完成的！）代码。请查看，尤其是query()和insert()函数： - ）

PhotoContract.java

package com.example.android.galleri.app.data;

import android.content.ContentResolver;
import android.content.ContentUris;
import android.net.Uri;
import android.provider.BaseColumns;
import android.provider.MediaStore;

public class PhotoContract {

    public static final String CONTENT_AUTHORITY = "no.myapp.android.galleri.app";

    public static final Uri BASE_CONTENT_URI = Uri.parse("content://" + CONTENT_AUTHORITY);

    public static final String PATH_PHOTO = "photo";
    public static final String PATH_COMMENT = "comment";

    public static final class PhotoEntry {

        public static final Uri CONTENT_URI =
                BASE_CONTENT_URI.buildUpon().appendPath(PATH_PHOTO).build();

        public static final String COLUMN_DISPLAY_NAME = MediaStore.Images.Media.DISPLAY_NAME;
        public static final String COLUMN_DATA = MediaStore.Images.Media.DATA;
        public static final String COLUMN_DESC = MediaStore.Images.Media.DESCRIPTION;
        public static final String COLUMN_DATE_TAKEN = MediaStore.Images.Media.DATE_TAKEN;
        public static final String COLUMN_DATE_ADDED = MediaStore.Images.Media.DATE_ADDED;
        public static final String COLUMN_TITLE = MediaStore.Images.Media.TITLE;
        public static final String COLUMN_SIZE = MediaStore.Images.Media.SIZE;
        public static final String COLUMN_ORIENTATION = MediaStore.Images.Media.ORIENTATION;
        public static final String COLUMN_EXIF_COMMENT = "UserComment";
        public static final String COLUMN_EXIF_AUTHOR = "Author";

        // should these simply be image/png??
        public static final String CONTENT_TYPE =
                ContentResolver.CURSOR_DIR_BASE_TYPE + "/" + CONTENT_AUTHORITY + "/" + PATH_PHOTO;
        public static final String CONTENT_ITEM_TYPE =
                ContentResolver.CURSOR_ITEM_BASE_TYPE + "/" + CONTENT_AUTHORITY + "/" + PATH_PHOTO;

        // makes an URI to a specific image_id
        public static final Uri buildPhotoWithId(Long photo_id) {
            return CONTENT_URI.buildUpon().appendPath(Long.toString(photo_id)).build();
        }

        // since we will "redirect" the URI towards MediaStore, we need to be able to extract IMAGE_ID
        public static Long getImageIdFromUri(Uri uri) {
            return Long.parseLong(uri.getPathSegments().get(1));  // TODO: is it position 1??
        }

        // get comment to set in EXIF tag
        public static String getCommentFromUri(Uri uri) {
            return uri.getPathSegments().get(2);  // TODO: is it position 2??
        }
    }
}

PhotoProvider.java：

package com.example.android.galleri.app.data;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.MatrixCursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.media.ExifInterface;
import android.net.Uri;
import android.provider.MediaStore;
import android.support.v4.content.CursorLoader;
import android.util.Log;

import java.io.IOException;


public class PhotoProvider extends ContentProvider {

    // The URI Matcher used by this content provider.
    private static final UriMatcher sUriMatcher = buildUriMatcher();

    static final int PHOTO = 100;
    static final int PHOTO_SET_COMMENT = 200;

    static UriMatcher buildUriMatcher() {
        // 1) The code passed into the constructor represents the code to return for the root
        // URI.  It's common to use NO_MATCH as the code for this case. Add the constructor below.
        final UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
        final String authority = PhotoContract.CONTENT_AUTHORITY;

        // 2) Use the addURI function to match each of the types.  Use the constants from
        // WeatherContract to help define the types to the UriMatcher.

        // matches photo/<any number> meaning any photo ID
        matcher.addURI(authority, PhotoContract.PATH_PHOTO + "/#", PHOTO);

        // matches photo/<photo id>/comment/<any comment>
        matcher.addURI(authority, PhotoContract.PATH_PHOTO + "/#/" + PhotoContract.PATH_COMMENT + "/*", PHOTO_SET_COMMENT);

        // 3) Return the new matcher!
        return matcher;
    }


    @Override
    public String getType(Uri uri) {

        // Use the Uri Matcher to determine what kind of URI this is.
        final int match = sUriMatcher.match(uri);

        switch (match) {
            case PHOTO_SET_COMMENT:
                return PhotoContract.PhotoEntry.CONTENT_TYPE;
            case PHOTO:
                return PhotoContract.PhotoEntry.CONTENT_TYPE;
            default:
                throw new UnsupportedOperationException("Unknown uri: " + uri);
        }
    }


    @Override
    public boolean onCreate() {
        return true;  // enough?
    }


    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        MatrixCursor retCursor = new MatrixCursor(projection);

        // open the specified image through the MediaStore to get base columns
        // then open image file through ExifInterface to get detail columns
        Long IMAGE_ID = PhotoContract.PhotoEntry.getImageIdFromUri(uri);

        //Uri baseUri = Uri.parse("content://media/external/images/media");
        Uri baseUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
        baseUri = Uri.withAppendedPath(baseUri, ""+ IMAGE_ID);

        String[] MS_projection = {
                MediaStore.Images.Media.DISPLAY_NAME,
                MediaStore.Images.Media.DATA,
                MediaStore.Images.Media.DESCRIPTION,
                MediaStore.Images.Media.DATE_TAKEN,
                MediaStore.Images.Media.DATE_ADDED,
                MediaStore.Images.Media.TITLE,
                MediaStore.Images.Media.SIZE,
                MediaStore.Images.Media.ORIENTATION};

        // http://androidsnippets.com/get-file-path-of-gallery-image
        Cursor c = getContext().getContentResolver().query(baseUri, MS_projection, null, null, null);

        // dump fields (the ones we want -- assuming for now we want ALL fields, in SAME ORDER) into MatrixCursor
        Object[] row = new Object[projection.length];
        row[0] = c.getString(0);  // DISPLAY_NAME
        row[1] = c.getBlob(1);  // etc
        row[2] = c.getString(2);
        row[3] = c.getLong(3);
        row[4] = c.getLong(4);
        row[5] = c.getString(5);
        row[6] = c.getInt(6);
        row[7] = c.getInt(7);

        // NB! Extra +2 fields, for EXIF data.
        try {
            ExifInterface exif = new ExifInterface((String)row[1]);
            row[8] = exif.getAttribute("UserComment");
            row[9] = exif.getAttribute("Author");

        } catch (IOException e) {
            e.printStackTrace();
        }

        retCursor.addRow(row);

        return retCursor;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        String comment_to_set = PhotoContract.PhotoEntry.getCommentFromUri(uri);
        Long IMAGE_ID = PhotoContract.PhotoEntry.getImageIdFromUri(uri);

        Uri baseUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
        baseUri = Uri.withAppendedPath(baseUri, ""+ IMAGE_ID);

        // get DATA (path/filename) from MediaStore -- only need that specific piece of information
        String[] MS_projection = {MediaStore.Images.Media.DATA};

        // http://androidsnippets.com/get-file-path-of-gallery-image
        Cursor c = getContext().getContentResolver().query(baseUri, MS_projection, null, null, null);
        String thumbData = c.getString(0);

        try {
            ExifInterface exif = new ExifInterface(thumbData);

            exif.setAttribute("UserComment", comment_to_set);
            exif.saveAttributes();

        } catch (IOException e) {
            e.printStackTrace();
        }
        return PhotoContract.PhotoEntry.buildPhotoWithId(IMAGE_ID);  // return URI to this specific image
    }

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

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

Answer 1

我相信我设法解决了这个问题，毕竟它并不是那么神秘。编写自定义内容，在这种情况下，提供程序真正归结为实现我自己的query和update方法。我不需要任何insert或delete，因为我只是正在阅读 MediaStore。

首先，我设计了两个URI;一个用于查询，一个用于更新。查询URI遵循模式content://AUTH/photo/#，其中＃是MediaStore.Images.Thumbnails中的IMAGE_ID。该方法基本上针对MediaStore.Images.Media运行另一个查询，以获得＆＃34;标准＆＃34;关于特定图像的数据，然后通过ExifInterface在图像上获得一些额外的元数据。所有这些都以MatrixCursor返回。

更新URI与模式content://AUTH/photo/#/comment匹配，然后设置（写入）具有该ID的文件中的UserComment EXIF标记 - 再次通过{{ 1}}。

要回答我的问题，我将从我的PhotoContract和PhotoProvider课程发布更新的代码。基本上，如果您正在编写一个内容提供程序，它不接口SQLite数据库 - 而是设备上的其他内容 - 您需要做的就是在适当的方法中实现这些操作你的提供者类。

PhotoContract

ExifInterface

PhotoProvider

import android.content.ContentResolver;
import android.content.ContentUris;
import android.net.Uri;
import android.provider.BaseColumns;
import android.provider.MediaStore;

public class PhotoContract {

    public static final String CONTENT_AUTHORITY = "com.example.android.myFunkyApp.app";

    public static final Uri BASE_CONTENT_URI = Uri.parse("content://" + CONTENT_AUTHORITY);

    public static final String PATH_PHOTO = "photo";
    public static final String PATH_COMMENT = "comment";
    //public static final String PATH_AUTHOR = "author";

    public static final class ThumbEntry {
        public static final String COLUMN_THUMB_ID = MediaStore.Images.Thumbnails._ID;
        public static final String COLUMN_DATA = MediaStore.Images.Thumbnails.DATA;
        public static final String COLUMN_IMAGE_ID = MediaStore.Images.Thumbnails.IMAGE_ID;
    }

    public static final class PhotoEntry {

        public static final Uri CONTENT_URI =
                BASE_CONTENT_URI.buildUpon().appendPath(PATH_PHOTO).build();

        public static final String COLUMN_IMAGE_ID = MediaStore.Images.Media._ID;
        public static final String COLUMN_DISPLAY_NAME = MediaStore.Images.Media.DISPLAY_NAME;
        public static final String COLUMN_DATA = MediaStore.Images.Media.DATA;
        public static final String COLUMN_DESC = MediaStore.Images.Media.DESCRIPTION;
        public static final String COLUMN_DATE_TAKEN = MediaStore.Images.Media.DATE_TAKEN;
        public static final String COLUMN_DATE_ADDED = MediaStore.Images.Media.DATE_ADDED;
        public static final String COLUMN_TITLE = MediaStore.Images.Media.TITLE;
        public static final String COLUMN_SIZE = MediaStore.Images.Media.SIZE;
        public static final String COLUMN_ORIENTATION = MediaStore.Images.Media.ORIENTATION;
        public static final String COLUMN_EXIF_COMMENT = "UserComment";
        //public static final String COLUMN_EXIF_AUTHOR = "Author";

        public static final String CONTENT_TYPE =
                ContentResolver.CURSOR_DIR_BASE_TYPE + "/" + CONTENT_AUTHORITY + "/" + PATH_PHOTO;
        public static final String CONTENT_ITEM_TYPE =
                ContentResolver.CURSOR_ITEM_BASE_TYPE + "/" + CONTENT_AUTHORITY + "/" + PATH_PHOTO;

        // makes an URI to a specific image_id
        public static final Uri buildPhotoUriWithId(Long photo_id) {
            return CONTENT_URI.buildUpon().appendPath(Long.toString(photo_id)).build();
        }

        // since we will "redirect" the URI towards MediaStore, we need to be able to extract IMAGE_ID
        public static Long getImageIdFromUri(Uri uri) {
            return Long.parseLong(uri.getPathSegments().get(1));  // always in position 1
        }

    }
}

在手机上为照片编写自定义内容提供商（第2部分）

PhotoContract.java

PhotoProvider.java：

1 个答案:

PhotoContract

PhotoProvider