这就是我现在正在使用的：

斯威夫特4.2

class TextField: UITextField {

    let padding = UIEdgeInsets(top: 0, left: 5, bottom: 0, right: 5)

    override open func textRect(forBounds bounds: CGRect) -> CGRect {
        return bounds.inset(by: padding)
    }

    override open func placeholderRect(forBounds bounds: CGRect) -> CGRect {
        return bounds.inset(by: padding)
    }

    override open func editingRect(forBounds bounds: CGRect) -> CGRect {
        return bounds.inset(by: padding)
    }
}

斯威夫特4

class TextField: UITextField {

    let padding = UIEdgeInsets(top: 0, left: 5, bottom: 0, right: 5)

    override open func textRect(forBounds bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }

    override open func placeholderRect(forBounds bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }

    override open func editingRect(forBounds bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }
}

斯威夫特3：

class TextField: UITextField {

    let padding = UIEdgeInsets(top: 0, left: 5, bottom: 0, right: 5)

    override func textRect(forBounds bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }

    override func placeholderRect(forBounds bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }

    override func editingRect(forBounds bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }
}

我从未设置其他填充，但是您可以进行调整。此类不会处理textfield上的rightView和leftView。如果您希望它得到正确处理，则可以使用类似（objc中的示例，我只需要rightView即可：

- (CGRect)textRectForBounds:(CGRect)bounds {
    CGRect paddedRect = UIEdgeInsetsInsetRect(bounds, self.insets);

    if (self.rightViewMode == UITextFieldViewModeAlways || self.rightViewMode == UITextFieldViewModeUnlessEditing) {
        return [self adjustRectWithWidthRightView:paddedRect];
    }
    return paddedRect;
}

- (CGRect)placeholderRectForBounds:(CGRect)bounds {
    CGRect paddedRect = UIEdgeInsetsInsetRect(bounds, self.insets);

    if (self.rightViewMode == UITextFieldViewModeAlways || self.rightViewMode == UITextFieldViewModeUnlessEditing) {
        return [self adjustRectWithWidthRightView:paddedRect];
    }
    return paddedRect;
}

- (CGRect)editingRectForBounds:(CGRect)bounds {
    CGRect paddedRect = UIEdgeInsetsInsetRect(bounds, self.insets);

    if (self.rightViewMode == UITextFieldViewModeAlways || self.rightViewMode == UITextFieldViewModeWhileEditing) {
        return [self adjustRectWithWidthRightView:paddedRect];
    }
    return paddedRect;
}

- (CGRect)adjustRectWithWidthRightView:(CGRect)bounds {
    CGRect paddedRect = bounds;
    paddedRect.size.width -= CGRectGetWidth(self.rightView.frame);

    return paddedRect;
}