【设计模式】备忘录模式

概念

行为模式

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类图

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代码

#include <iostream>using namespace std;class Snapshot;
class Editor {
public:void SetText(const string& t) {text = t;}void SetCursor(int x, int y) {this->curX = x;this->curY = y;}void SetSelectionWidth(int width) {selectionWidth = width;}Snapshot* CreateSnapshot(const string& t, int x, int y, int w) {cout << "Create Snapshot." << endl;return nullptr;// return new Snapshot(this, t, x, y, w); // cannot implement in one cpp file}private:string text;int curX{}, curY{};int selectionWidth{};
};class Snapshot {
public:Snapshot(Editor* e, const string& t, int x, int y, int w) {editor = e;text = t;curX = x;curY = y;selectionWidth = w;};void Restore() {cout << "Restore from snapshot." << endl;editor->SetText(text);editor->SetCursor(curX, curY);editor->SetSelectionWidth(selectionWidth);}private:Editor* editor;string text;int curX, curY;int selectionWidth;
};class Command {
public:void MakeBackup(Editor* editor, const string& t, int x, int y, int w) {backup = editor->CreateSnapshot(t, x, y, w);}void Undo() {if (backup != nullptr) {backup->Restore();}}private:Snapshot* backup;
};int main(int argc, char *argv[]) {auto editor = new Editor();auto command = new Command();command->MakeBackup(editor, "Older State", 1, 2, 3);editor->SetText("Newer State");editor->SetCursor(2, 3);command->Undo();delete command;delete editor;return 0;
}