Question

我的sqlite数据库中有2个表，所以现在我正在尝试为数据库创建内容提供程序。我到目前为止看到的所有例子只显示了2个表的CRUD代码，但没有显示checkColumns。我试过这个

private void checkColumns(String[] projection) {

    if (Constants.COLUMNS != null) {
        HashSet<String> requestedColumns = new HashSet<String>(Arrays.asList(projection));
        HashSet<String> availableColumns = new HashSet<String>(Arrays.asList(Constants.COLUMNS));
        if (!availableColumns.containsAll(requestedColumns)) {
            throw new IllegalArgumentException("Unknown columns in projection");
        }
    }
    if (Constants.pCOLUMNS != null) {
        HashSet<String> requestedColumns = new HashSet<String>(Arrays.asList(projection));
        HashSet<String> availableColumns = new HashSet<String>(Arrays.asList(Constants.pCOLUMNS));
        if (!availableColumns.containsAll(requestedColumns)) {
            throw new IllegalArgumentException("Unknown columns in projection");
        }
    }
}

然后对于查询，我做了这个

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
    checkColumns(Constants.COLUMNS);
    checkColumns(Constants.pCOLUMNS);
    queryBuilder.setTables(Constants.ITEM_TABLE);
    queryBuilder.setTables(Constants.PANTRY_TABLE);

    int type = URI_MATCHER.match(uri);
    switch (type) {
        case ITEMS:
            break;
        case ITEM:
            queryBuilder.appendWhere(Constants.COLUMN_iID + " = " + uri.getLastPathSegment());
            break;
        case sPANTRY:
            break;
        case PANTRY:
            queryBuilder.appendWhere(Constants.COLUMN_pID + " = " + uri.getLastPathSegment());
            break;
        default:
            throw new IllegalArgumentException("Unknown URI: " + uri);
    }
    SQLiteDatabase db = dbHelper.getWritableDatabase();
    Cursor cursor = queryBuilder.query(db, projection, selection, selectionArgs, null, null, sortOrder);
    cursor.setNotificationUri(getContext().getContentResolver(), uri);
    return cursor;
}

来自Constants.java的

public static final String[] COLUMNS = {
        Constants.COLUMN_iID,
        Constants.COLUMN_ITEM,
        Constants.COLUMN_iQUANTITY,
        Constants.COLUMN_iUNIT,
        Constants.COLUMN_PRICE,
        Constants.COLUMN_STORE

};

public static final String[] pCOLUMNS = {
        Constants.COLUMN_pID,
        Constants.COLUMN_PANTRY,
        Constants.COLUMN_pQUANTITY,
        Constants.COLUMN_pUNIT,
        Constants.COLUMN_EXPIRY_DATE
};
}

但我收到此错误

Caused by: java.lang.IllegalArgumentException: Unknown columns in projection

我尝试在checkColumns中使用switch case，如此

private void checkColumns(String[] projection) {
    switch(projection) {
        case Constants.COLUMNS:
            HashSet<String> requestedColumns = new HashSet<String>(Arrays.asList(projection));
            HashSet<String> availableColumns = new HashSet<String>(Arrays.asList(Constants.COLUMNS));
            if (!availableColumns.containsAll(requestedColumns)) {
                throw new IllegalArgumentException("Unknown columns in projection");
            }
            break;
        case Constants.pCOLUMNS:
            HashSet<String> requestedColumns = new HashSet<String>(Arrays.asList(projection));
            HashSet<String> availableColumns = new HashSet<String>(Arrays.asList(Constants.pCOLUMNS));
            if (!availableColumns.containsAll(requestedColumns)) {
                throw new IllegalArgumentException("Unknown columns in projection");
            }
           break;
    }
}

但我需要不断表达＆＃39;在两个常数上。

Answer 1

你得到“需要常量表达式”错误，因为checkColumns(String[] projection)方法采用字符串数组，并且switch语句不能使用字符串数组作为“switch”变量。

第一种方法似乎没问题。您得到java.lang.IllegalArgumentException可能是因为requestedColumns和availableColumns中存在不匹配（例如，可用列中不存在请求的列）。

假设逻辑是检查所有投影列是否在items和pantry列中，那么可以将Constants.COLUMNS和Constants.pCOLUMNS添加到一个数组中（比如“totalColumns”），然后进行检查：< / p>

private void checkColumns(String[] projection) {
    if (projection != null) {
        String[] totalColumns = ArrayUtils.addAll(Constants.COLUMNS, Constants.pCOLUMNS);
        if (!totalColumns.containsAll(requestedColumns)) {
                throw new IllegalArgumentException("Unknown columns in projection");
        }
    } else {
        throw new IllegalArgumentException("Invalid column projection");
    }
}

（请注意，您需要导入ArrayUtils，或者如果您不想导入它，您可以编写自己的...，无论如何，您明白了。）

Android内容提供商 - 如何检查多个表的列

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