Detect moment when newline starts in UITextView

问题

I try to detect when carriage goes at new line in UITextView. I can detect it by comparison total later width with UITextView width:

CGSize size = [textView.text sizeWithAttributes:textView.typingAttributes];
if(size.width > textView.bounds.size.width)
      NSLog (@"New line");

But it dose not work proper way because -sizeWithAttributes:textView returns only width of letters without indentation width. Help please solve this.

回答1:

This is how I would do it:

Get the UITextPosition of the last character.
Call caretRectForPosition on your UITextView.
Create a CGRect variable and initially store CGRectZero in it.
In your textViewDidChange: method, call caretRectForPosition: by passing the UITextPosition.
Compare it with the current value stored in the CGRect variable. If the new y-origin of the caretRect is greater than the last one, it means a new line has been reached.

Sample code:

CGRect previousRect = CGRectZero;
- (void)textViewDidChange:(UITextView *)textView{

    UITextPosition* pos = yourTextView.endOfDocument;//explore others like beginningOfDocument if you want to customize the behaviour
    CGRect currentRect = [yourTextView caretRectForPosition:pos];

    if (currentRect.origin.y > previousRect.origin.y){
            //new line reached, write your code
        }
    previousRect = currentRect;

}

Also, you should read the documentation for UITextInput protocol reference here. It is magical, I'm telling you.

Let me know if you have any other issues with this.

回答2:

For Swift use this

previousRect = CGRectZero

 func textViewDidChange(textView: UITextView) {

        var pos = textView.endOfDocument
        var currentRect = textView.caretRectForPosition(pos)
        if(currentRect.origin.y > previousRect?.origin.y){
            //new line reached, write your code
        }
        previousRect = currentRect

    }

回答3:

answer of @n00bProgrammer in Swift-4 with more precise line break detection.

@n00bProgrammer answer is perfect except one thing it reacts differently when the user starts typing in a first line, it presents that Started New Line too.
Overcoming issue, here is the refined code

    var previousRect = CGRect.zero
    func textViewDidChange(_ textView: UITextView) {
        let pos = textView.endOfDocument
        let currentRect = textView.caretRect(for: pos)
        self.previousRect = self.previousRect.origin.y == 0.0 ? currentRect : self.previousRect
        if currentRect.origin.y > self.previousRect.origin.y {
            //new line reached, write your code
            print("Started New Line")
        }
        self.previousRect = currentRect
    }

回答4:

Swift 3

The accepted answer and the swift version works fine, but here is a Swift 3 version for the lazy people out there.

class CustomViewController: UIViewController, UITextViewDelegate {

    let textView = UITextView(frame: .zero)
    var previousRect = CGRect.zero

    override func viewDidLoad(){
        textView.frame = CGRect(
            x: 20, 
            y: 0, 
            width: view.frame.width, 
            height: 50
        )
        textView.delegate = self
        view.addSubview(textView)
    }

    func textViewDidChange(_ textView: UITextView) {
        let pos = textView.endOfDocument
        let currentRect = textView.caretRect(for: pos)
        if previousRect != CGRect.zero {
            if currentRect.origin.y > previousRect.origin.y {
                print("new line")
            }
        }
        previousRect = currentRect
    }
}

回答5:

You can use the UITextViewDelegate

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText: (NSString *)text
{
     BOOL newLine = [text isEqualToString:@"\n"];
     if(newLine)
     {
          NSLog(@"User started a new line");
     }
     return YES;
}

回答6:

You need to get the height of the text, not the width. Use either sizeWithFont:constrainedToSize:lineBreakMode: (if you need to support iOS 6 or earlier) or use boundingRectWithSize:options:attributes:context: if you only support iOS 7.

回答7:

SWIFT 4

If you don't want to use previousRect. Let's try this:

func textViewDidChange(_ textView: UITextView) {
    let pos = textView.endOfDocument
    let currentRect = textView.caretRect(for: pos)
    if (currentRect.origin.y == -1 || currentRect.origin.y == CGFloat.infinity){
       print("Yeah!, I've gone to a new line") 
       //-1 for new line with a char, infinity is new line with a space
    }
}

来源：https://stackoverflow.com/questions/20008713/detect-moment-when-newline-starts-in-uitextview

标签

ios

objective-c

nsstring

uitextview