为什么赋值在 Dart 中的工作方式与在 Python 中不同？

Question

当我运行这段代码时：

void readCard(db, [int card_id = -1]) {
    if (card_id == -1) {
        final ResultSet result = db.select('SELECT * FROM cards');
    }

    else {
        final ResultSet result = db.select("""
                SELECT * FROM cards
                WHERE card_id=(?)
                """); // this doesn't work yet
    }

    for (final Row card in result) {
        print(
                "Card {'card_id': ${card['card_id']}, "
                "'due': ${card['due']}, "
                "'content': ${card['content']}}"
                );
    }
}

我收到这个错误：

memotext.dart:66:25: Error: Getter not found: 'result'.
        for (final Row card in result) {
                               ^^^^^^

因为result不管是if语句还是else语句运行s都赋值了应该不会出错吧？这与 dart 的赋值方式有关吗？

Answer 1

结果在各自的块中声明，它不存在于外部。这样做：

void readCard(db, [int card_id = -1]) {
    ResultSet result;
    if (card_id == -1) {
        result = db.select('SELECT * FROM cards');
    }

    else {
        result = db.select("""
                SELECT * FROM cards
                WHERE card_id=(?)
                """); // this doesn't work yet
    }

    for (final Row card in result) {
        print(
                "Card {'card_id': ${card['card_id']}, "
                "'due': ${card['due']}, "
                "'content': ${card['content']}}"
                );
    }
}

为什么赋值在 Dart 中的工作方式与在 Python 中不同？

Why does assignment not work the same in Dart as it does in Python?

dart

assign