如何在Qt5中"merge"两个QVariantMap的内容？

Question

我有两个QVariantMap实例A和B。

在A中，我有以下字符串：[ "key1" => "Cat", "key2" => "Dog", "key3" => "Mouse" ]。在B中，我有以下字符串：[ "key1" => "Cat", "key4" => "Dog", "key3" => "Bison" ]。

我想将它们合并到第三个QVariantMap实例C中，以便它包含以下内容：

[ "key1" => "Cat", "key2" => "Dog", "key3" => "Bison", "key4" => "Dog" ]。

注意如何只有一只"猫"，以及"老鼠"是如何被"野牛"取代的。

有没有一种方法可以在Qt5中做到这一点，而无需编写自己的实用程序函数？

Answer 1

QVariantMap A;
QVariantMap B;
QVariantMap C;
A.insert("key1", "Cat");
A.insert("key2", "Dog");
A.insert("key3", "Mouse");
B.insert("key1", "Cat");
B.insert("key4", "Dog");
B.insert("key3", "Bison");
//Merge A and B
C = A.unite(B);
//C.value("key1") = "Cat" 
//C.value("key3") = "Bison"
//C.values("key3") = {"Bison", "Mouse"}
//C.values("key1") = {"Cat", "Cat"}
//Note: A = C as well. If you don't want to change the value of A, then assign a temporary value to A or create a copy of A
//Method 1: Create a copy of A
QVariantMap ACopy = A;
C = ACopy.unite(B);
//Method 2: Create a temporary variable that hold A value:
QVariantMap ATemp = A;
C = A.unite(B);
A = ATemp;

Answer 2

自5.15以来，Qt提供了一个以另一个QMap为参数的insert重载，它将其他映射中的所有键/值对插入到原始映射中，覆盖现有键：

    QVariantMap A;
    QVariantMap B;
    A.insert("key1", "Cat");
    A.insert("key2", "Dog");
    A.insert("key3", "Mouse");
    B.insert("key1", "Cat");
    B.insert("key4", "Dog");
    B.insert("key3", "Bison");
    QVariantMap C(A);
    C.insert(B);
    // C now holds the combined keys&values of A & B;
    // for keys existing in both A and B, the values from B are taken!

Answer 3

QVarianMap C(A); // copy-construct C from A
for (auto i = B.constBegin(); i != B.constEnd(); ++i)
{
     C.insert(i.key(), i.value()); // add B's element to C replacing C's entry with the same key if such exists
}