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How to implement the Command class Command class in Konva.js to support undo and redo functions?
How to implement the Command class Command class in Konva.js to support undo and redo functions?
Apr 04, 2025 pm 04:30 PM
Implementation of undo redo function based on command mode in Konva.js
This article introduces how to use command mode to implement the undo (Ctrl Z) and redo (Ctrl Y) functions in the Konva.js drawing application. We encapsulate graphical operations into command objects and manage these operations using a command stack to achieve fallback and progress in graphical editing.
First, define a basic Command class:
class Command {
constructor() {
this.states = []; // Used to store state snapshots}
execute() {
throw new Error('execute method must be implemented');
}
undo() {
throw new Error('undo method must be implemented');
}
saveState(state) {
this.states.push(state);
}
restoreState() {
return this.states.pop() || null; // Return to the previous state, or null
}
}
Next, create a specific command class, such as the command to draw a rectangle:
class DrawRectangleCommand extends Command {
constructor(stage, layer, rect) {
super();
this.stage = stage;
this.layer = layer;
this.rect = rect;
}
execute() {
this.saveState(this.layer.toJSON()); // Save the current layer state this.layer.add(this.rect);
this.layer.draw();
}
undo() {
this.rect.destroy();
const prevState = this.restoreState();
if (prevState) {
this.layer.destroyChildren(); // Clear the layer this.layer = Konva.Node.create(prevState, this.stage); // Restore the previous state this.stage.add(this.layer);
this.layer.draw();
}
}
}
Then, implement the command manager:
class CommandManager {
constructor() {
this.undoStack = [];
this.redoStack = [];
}
executeCommand(command) {
command.execute();
this.undoStack.push(command);
this.redoStack = []; // After executing the new command, clear the redo stack}
undo() {
if (this.undoStack.length === 0) return;
const command = this.undoStack.pop();
command.undo();
this.redoStack.push(command);
}
redo() {
if (this.redoStack.length === 0) return;
const command = this.redoStack.pop();
command.execute();
this.undoStack.push(command);
}
}
Finally, use in the Konva.js application:
const stage = new Konva.Stage({
container: 'container',
width: window.innerWidth,
height: window.innerHeight
});
const layer = new Konva.Layer();
stage.add(layer);
const commandManager = new CommandManager();
stage.on('click', (e) => {
const rect = new Konva.Rect({
x: e.evt.layerX,
y: e.evt.layerY,
width: 50,
height: 50,
fill: 'red',
draggable: true
});
const command = new DrawRectangleCommand(stage, layer, rect);
commandManager.executeCommand(command);
});
document.addEventListener('keydown', (e) => {
if (e.ctrlKey && e.key === 'z') {
commandManager.undo();
} else if (e.ctrlKey && e.key === 'y') {
commandManager.redo();
}
});
This code implements simple rectangle drawing and undo redoing. You can extend Command class to support other graphical operations such as movement, scaling, rotation, etc. Remember to save the current state in the execute method of each operation and restore the previous state in the undo method. This will ensure that your undo redo feature works correctly.
The above is the detailed content of How to implement the Command class Command class in Konva.js to support undo and redo functions?. For more information, please follow other related articles on the PHP Chinese website!
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