实现NSUndoManager

Question

我在实现NSUndoManager时遇到了困难，我试着阅读了苹果的文档，但我不能理解它。这就是我到目前为止所尝试的。我已经创建了一个通过连接数组中的两个点来绘制线条的应用程序，我通过移除最后一个对象实现了一个撤销方法，但是我不知道如何实现重做，我偶然发现了NSUndoManager并开始阅读它的文档，但我不知道如何将它应用到我的问题中。这是我目前拥有的代码

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    NSUInteger taps = [[touches anyObject]tapCount];
    if(taps == 2) {
        [self setNeedsDisplay];
    }
    else {
        if([self.pointsArray count] == 0) {
            self.pointsArray = [[NSMutableArray alloc]init];
            UITouch *t = [touches anyObject];
            CGPoint startLoc = [t locationInView:self];
            [self.pointsArray addObject:[NSValue valueWithCGPoint:startLoc]];
        }
    }
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *t = [touches anyObject];
    CGPoint currentLoc = [t locationInView:self];
    [self.pointsArray addObject:[NSValue valueWithCGPoint:currentLoc]];
    [self setNeedsDisplay];
}

#pragma mark - Undo/Redo Methods
-(void)undo:(id) object {
    [[undoManager prepareWithInvocationTarget:self]redo:object];
    [undoManager setActionName:@"undoLineSegment"];
    [self.pointsArray removeLastObject];
}

-(void)redo:(id)object {
    [self.pointsArray addObject:object];
    [[undoManager prepareWithInvocationTarget:self]undo:object];
    [undoManager setActionName:@"RedoUndoneLineSegment"];
}

- (IBAction)undoButton:(UIButton *)sender {
    [self.undoManager undo];
    [self setNeedsDisplay];
}

- (IBAction)redoButton:(UIButton *)sender {
    [self.undoManager redo];
    [self setNeedsDisplay];
}

我没有收到任何错误，但在运行时，当我点击按钮时，什么也没有发生。关于NSUndoManager，我不理解的是事物的去向，“对象”是什么。我不是在声明一些我需要声明的东西吗。

谢谢,

Answer 1

当您绘制直线时，touchesMoved方法将调用多次，因此，如果在touchesMoved方法中注册undo操作，则需要对它们进行分组：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self.undoManager beginUndoGrouping];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self.undoManager endUndoGrouping];
}

这是一个example。

Answer 2

Swift 4.*和Xcode9.3中的完整示例

import UIKit

class ViewController: UIViewController {


    @IBOutlet weak var colorsCollectionView: UICollectionView!

    @IBOutlet weak var colorView: UIView!

    var colorsArray = ["green","blue","red","black","yellow","brown","orange","purple","cyan","magenta"]

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func redoAction(_ sender: Any) {
        undoManager?.redo()
    }

    @IBAction func undoAction(_ sender: Any) {
        undoManager?.undo()
    }

    func changeColor(color: UIColor) {

        let oldColor = self.colorView.backgroundColor ?? UIColor.white
        undoManager?.registerUndo(withTarget: self, handler: { (targetSelf) in
            targetSelf.changeColor(color: oldColor)
        })
        colorView.backgroundColor = color
    }

}


extension ViewController: UICollectionViewDelegate,UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return colorsArray.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)

        let label:UILabel = cell.viewWithTag(101) as! UILabel
        label.text = colorsArray[indexPath.row]

        return cell
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let colorName = colorsArray[indexPath.row]

        switch colorName {
        case "green":
            changeColor(color: UIColor.green)
        case "blue":
            changeColor(color: UIColor.blue)
        case "red":
            changeColor(color: UIColor.red)
        case "black":
            changeColor(color: UIColor.black)
        case "yellow":
            changeColor(color: UIColor.yellow)
        case "brown":
            changeColor(color: UIColor.brown)
        case "orange":
            changeColor(color: UIColor.orange)
        case "purple":
            changeColor(color: UIColor.purple)
        case "cyan":
            changeColor(color: UIColor.cyan)
        case "magenta":
            changeColor(color: UIColor.magenta)
        default:
            changeColor(color: UIColor.white)
        }
    }
}

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