android - 从 Custom Content Provider 访问数据

Question

我有两个基于内容提供程序的应用程序 A 和 B。它们都有自己的内容提供程序，并且设置为从 A 和 B 读取数据，反之亦然。当其他应用程序处于后台时，一切正常。但如果应用程序被终止或不在后台出现，则无法找到其他内容提供者。例如，应用程序 B 想从应用程序 A 读取数据。当 'A' 在后台运行时，'B' 可以从 'A' 成功读取数据，但如果 'A' 未运行，则会出现 fatal error (找不到匹配的 uri)在后台。

有什么想法吗？

[编辑]我遇到了与 this post 相同的问题.我在两个应用程序的 list 中都有:

   <provider
        android:name="MyContentProvider"
        android:authorities="com.example.${applicationId}-provider"
        android:enabled="true"
        android:exported="true"
        android:grantUriPermissions="true">
    </provider>

这是我遇到的错误:

Writing exception to parcel java.lang.IllegalArgumentException: Unsupported URI(Query): content://com.example.appA-provider/appA at com.example.provider.MyContentProvider.query(MyContentProvider.java:142) at android.content.ContentProvider.query(ContentProvider.java:1007) at android.content.ContentProvider$Transport.query(ContentProvider.java:218) at android.content.ContentProviderNative.onTransact(ContentProviderNative.java:112) at android.os.Binder.execTransact(Binder.java:461)

注意:只有当另一个应用程序不在后台时才会发生这种情况，否则它会按预期工作(可以正常读取彼此的数据)。

[编辑 2]这是 MyContentProvider 的代码:

package com.example.provider;

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


public class MyContentProvider extends ContentProvider {

    private static DatabaseHelper dbHelper;

    private static final int ALL_ENTRIES = 1;
    private static final int SINGLE_ENTRY = 2;

    private String mAuthority = BuildConfig.APPLICATION_ID;
    private static UriMatcher uriMatcher;

    public Uri CONTENT_URI= null;

    static {
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    }

    public MyContentProvider() {}

    public void init(String packageName, String authority) {
        if (authority == null) {
            setAuthority(packageName, true);
        } else {
            setAuthority(authority, false);
        }

        uriMatcher.addURI(getAuthority(), TABLE_NAME, ALL_ENTRIES);
        uriMatcher.addURI(getAuthority(), TABLE_NAME + "/#", SINGLE_ENTRY);
        CONTENT_URI =
                Uri.parse("content://" + getAuthority() + "/" + TABLE_NAME);
    }

    private void setAuthority(String packageName, boolean isPackageName) {
        if (isPackageName) {
            mAuthority = packageName + ".myprovider";
        } else {
            mAuthority = packageName;
        }
    }

    public String getAuthority() {
        return mAuthority;
    }

    public Uri getContentUri() {
        return CONTENT_URI;
    }

    @Override
    public boolean onCreate() {
        dbHelper = new DatabaseHelper(getContext());
        return false;
    }

    //Return the MIME type corresponding to a content URI
    @Override
    public String getType(Uri uri) {

        if (uri == null) {
            throw new IllegalArgumentException("Content uri is null: " + uri);
        }
        if (uriMatcher == null) {
            throw new IllegalArgumentException("Unsupported Match URI: " + uri);
        }

        switch (uriMatcher.match(uri)) {
            case ALL_ENTRIES:
                return "vnd.android.cursor.dir/vnd." + getAuthority() + "." + TABLE_NAME;
            case SINGLE_ENTRY:
                return "vnd.android.cursor.item/vnd." + getAuthority() + "." + TABLE_NAME;
            default:
                throw new IllegalArgumentException("Unsupported URI: " + uri);
        }
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        Uri _uri = null;
        long id = 0;
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        switch (uriMatcher.match(uri)) {
            case ALL_ENTRIES:
            case SINGLE_ENTRY:
                id = db.insert(TABLE_NAME, null, values);
                getContext().getContentResolver().notifyChange(uri, null);
                _uri = Uri.parse(CONTENT_URI + "/" + id);
                break;
            default:
                throw new IllegalArgumentException("Unsupported URI (insert): " + uri);
        }

        return _uri;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {

        SQLiteDatabase db = dbHelper.getWritableDatabase();
        SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

        Cursor cursor = null;
        String id = null;

        switch (uriMatcher.match(uri)) {
            case ALL_ENTRIES:
                queryBuilder.setTables(TABLE_NAME);
                cursor = queryBuilder.query(db, projection, selection,
                        selectionArgs, null, null, sortOrder);
                break;
            case SINGLE_ENTRY:
                queryBuilder.setTables(TABLE_NAME);
                id = uri.getPathSegments().get(1);
                if (id != null && !id.isEmpty()) {
                    queryBuilder.appendWhere(TABLE_NAME + "=" + id);
                }

                cursor = queryBuilder.query(db, projection, selection,
                        selectionArgs, null, null, sortOrder);
                break;
            default:
                throw new IllegalArgumentException("Unsupported URI(Query): " + uri);
        }

        return cursor;
    }
}

Answer 1

您不能像这样从代码中的其他地方初始化内容提供程序，因为 ContentProvider 可能是应用程序中第一个(或唯一)实例化的组件。

但是，您可以从 Manifest 或 String 资源中动态读取权限。在我对 Does Android Content Provider authority definition break the DRY rule? 的回答中我在 OpenTasks-Provider 中概述了我们是如何做到这一点的。