使用UITextView在UIView中以编程方式添加约束

我在UITextView中以编程方式添加了约束，但是尾部约束和底部约束无法正常工作。其他人工作正常。我认为UITextView框架大小不正确。

我只想以编程方式在UITextView中添加边距。

我的代码是

    let textView = UITextView()
    self.view.addSubview(textView)

    var constraints = [NSLayoutConstraint]()

    constraintTop = NSLayoutConstraint(item: textView,
        attribute: NSLayoutAttribute.Top,
        relatedBy: NSLayoutRelation.Equal,
        toItem: self.view,
        attribute: NSLayoutAttribute.Top,
        multiplier: 1.0,
        constant: 10)
    constraints.append(constraintTop)

    constraintBottom = NSLayoutConstraint(item: textView,
        attribute: NSLayoutAttribute.Bottom,
        relatedBy: NSLayoutRelation.Equal,
        toItem: self.view,
        attribute: NSLayoutAttribute.Bottom,
        multiplier: 1.0,
        constant: 10)
    constraints.append(constraintBottom)

    constraintLeft = NSLayoutConstraint(item: textView,
        attribute: NSLayoutAttribute.Leading,
        relatedBy: NSLayoutRelation.Equal,
        toItem: self.view,
        attribute: NSLayoutAttribute.Leading,
        multiplier: 1.0,
        constant: 10)
    constraints.append(constraintLeft)

    constraintRight = NSLayoutConstraint(item: textView,
        attribute: NSLayoutAttribute.Trailing,
        relatedBy: NSLayoutRelation.Equal,
        toItem: self.view,
        attribute: NSLayoutAttribute.Trailing,
        multiplier: 1.0,
        constant: 10)
    constraints.append(constraintRight)

    self.view.addConstraints(constraints)