允许在不暴露对象实现细节的情况下，将对象恢复到之前的状态。
快照发起者可以实现restore(Momento* m)方法，也可以由快照实现restore()方法。后者可以将快照对象与照看者对象（CareTaker）解耦。
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| class Editor {
private:
std::string text;
int curX, curY, selectionWidth;
public:
void setText(std::string t) {
text = t;
}
void setCursor(int x, int y) {
curX = x;
curY = y;
}
void setSelectionWdith(int w) {
selectionWidth = w;
}
Snapshot* createSnapshot() {
return new Snapshot(this, text, curX, curY, selectionWidth);
}
};
class Snapshot {
private:
Editor* editor;
std::string text;
int curX, curY, selectionWidth;
public:
Snapshot(Editor* e, std::string t, int x, int y, int w): editor(e), text(t), curX(x), curY(y), selectionWidth(w) {}
void restore() {
editor->setText(text);
editor->setCursor(curX, curY);
editor->setSelectionWidth(selectionWidth);
}
};
class Command {
private:
Snapshot* backup;
Editor* editor;
public:
Command(Editor* e): editor(e), backup(nullptr) {}
void makeBackup() {
backup = editor->createSnapshot();
}
void undo() {
if (backup) backup->restore();
}
virtual void execute() = 0;
};
class CopyCommand: public Command {
void execute() override {
}
};
|
