How to get current touch point and previous touch

问题:

I am new to iOS, I am using UIPanGestureRecognizer in my project. In which I have a requirement to get current touch point and previous touch point when I am dragging the view. I am struggling to get these two points.

If I use touchesBegan method Instead of using UIPanGestureRecognizer, I could get these two points by the following code:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    CGPoint touchPoint = [[touches anyObject] locationInView:self];
    CGPoint previous=[[touches anyObject]previousLocationInView:self];
}

I need to get these two points in UIPanGestureRecognizer event fire method. How can I achieve this? please guide me.

回答1:

You can use this:

CGPoint currentlocation = [recognizer locationInView:self.view];

Store previous location by setting current location if not found and adding current location everytime.

previousLocation = [recognizer locationInView:self.view]; 

回答2:

When you link an UIPanGestureRecognizer to an IBAction, the action will get called on every change. The gesture recognizer also provides a property called state which indicates if it's the first UIGestureRecognizerStateBegan, the last UIGestureRecognizerStateEnded or just an event between UIGestureRecognizerStateChanged.

To solve your problem, try it like the following:

- (IBAction)panGestureMoveAround:(UIPanGestureRecognizer *)gesture {
    if ([gesture state] == UIGestureRecognizerStateBegan) {
        myVarToStoreTheBeganPosition = [gesture locationInView:self.view];
    } else if ([gesture state] == UIGestureRecognizerStateEnded) {
       CGPoint myNewPositionAtTheEnd = [gesture locationInView:self.view];
       // and now handle it ;)
    }
}

You may also have a look at the method called translationInView:.

回答3:

There is a function in UITouch to get the previous touch in the view

• (CGPoint)locationInView:(UIView *)view;
• (CGPoint)previousLocationInView:(UIView *)view;

回答4:

You should instantiate your pan gesture recognizer as follows:

UIPanGestureRecognizer* panRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];

Then you should add panRecognizer to your view:

[aView addGestureRecognizer:panRecognizer];

The - (void)handlePan:(UIPanGestureRecognizer *)recognizer method will be called while the user interacts with the view. In handlePan: you can get the point touched like this:

CGPoint point = [recognizer locationInView:aView];

You can also get the state of the panRecognizer:

if (recognizer.state == UIGestureRecognizerStateBegan) {
    //do something
} else if (recognizer.state == UIGestureRecognizerStateEnded) {
   //do something else
}

回答5:

If you don't want to store anything you can also do this :

let location = panRecognizer.location(in: self)
let translation = panRecognizer.translation(in: self)
let previousLocation = CGPoint(x: location.x - translation.x, y: location.y - translation.y)