不等式約束以編程方式快速

Question

因此，我已經使用代碼完全編寫了我的應用程序的整個設置vc（沒有故事板），我想知道如何創建您創建不等式約束的約束？這意味着，如果應用程序運行在iPhone 7上，那麼約束條件會與我編碼的一樣，但是當您在iPhone上運行應用程序時，一切都會彼此重疊，而不是正確的比例。我只知道如何在故事板中使用不等式來做到這一點，但是如何在代碼中實現？這是我第一次不使用故事板，所以我有點新。

預先感謝您！

的制約因素是什麼的一些代碼的樣子：

func setupProfileImageView() { 
    //need x, y, width, height constraints 
    profileImageView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true 
    profileImageView.topAnchor.constraint(equalTo: view.topAnchor, constant: 120).isActive = true 
    profileImageView.widthAnchor.constraint(equalToConstant: 160).isActive = true 
    profileImageView.heightAnchor.constraint(equalToConstant: 160).isActive = true 

} 

Answer 1

只需創建兩個約束 - 一個用於最小值（greaterThanOrEqualTo）和一個用於最大值（lessThanOrEqualTo）。

myButton.widthAnchor.constraint(greaterThanOrEqualToConstant: 60).isActive = true 
myButton.widthAnchor.constraint(lessThanOrEqualToConstant: 120).isActive = true 

有一些技巧，如果你需要設置優先級做的，但它不會出現，你需要。如果你已經將置於一切正確（X和Y）這應該做到這一點。

Answer 2

你最簡單的選擇將是留在你的方法，並應用基於算法的常量。例如：

func setupProfileImageView() { 
    //need x, y, width, height constraints 

    var idealTop : CGFloat = view.frame.height * (some value) //so that it equals a value that changes with each screen size in a way that you feel ok with 

    idealTop = idealTop < 60 ? 60 : idealTop //makes sure that the constraint doesnt fall bellow 60.. 

    profileImageView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true 
    profileImageView.topAnchor.constraint(equalTo: view.topAnchor, constant: idealTop).isActive = true 
    profileImageView.widthAnchor.constraint(equalToConstant: 160).isActive = true 
    profileImageView.heightAnchor.constraint(equalToConstant: 160).isActive = true 

} 

其次，我會建議爲意味着元素被垂直對齊，並在視圖層次結構的同一水平線上，通過類似的方式疏遠他們任何佈局，並通過確保每個元素的topAnchor指的是它上面的元素bottomAnchor。一個小技巧，你可以做的，就是你的profileImage的topAnchor的值存儲到一個變量，這樣就可以訪問它的價值的其他元素，就像這樣：

var profileImageTopAnchor : NSLayoutConstraint? 

func setupProfileImageView() { 
    //need x, y, width, height constraints 

    var idealTop : CGFloat = view.frame.height * (some value) //so that it equals a value that changes with each screen size in a way that you feel ok with 

    idealTop = idealTop < 60 ? 60 : idealTop //makes sure that the constraint doesnt fall bellow 60.. 

    profileImageView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true 
    profileImageTopAnchor = profileImageView.topAnchor.constraint(equalTo: view.topAnchor, constant: idealTop) 
    profileImageTopAnchor.isActive = true //otherwise it wont get activated 
    profileImageView.widthAnchor.constraint(equalToConstant: 160).isActive = true 
    profileImageView.heightAnchor.constraint(equalToConstant: 160).isActive = true 

} 
func setupProfileImageView() { 

    let topAnchor = profileImageTopAnchor != nil ? profileImageTopAnchor!.constant : (/*Some arbitrary value here .. or repeat as above with a fraction value of the view.frame*/) 

    let topAnchorValue : CGFloat = topAnchor * (some value) //this way, the spacing will change based on the spacing you declare on top of your image.. 

    //And say that you have three other elements stacked vertically.. 

    elementA.constraint(equalTo: profileImageView.topAnchor, constant: topAnchorValue).isActive = true 
    elementB.constraint(equalTo: elementA.topAnchor, constant: topAnchorValue).isActive = true 
    elementC.constraint(equalTo: elementB.topAnchor, constant: topAnchorValue).isActive = true 
} 

你可以去進一步進入檢測實際屏幕大小，並將其與列表相關聯，以查看使用哪個手機型號..然後應用特定約束......但隨着此句越來越長，上述方法更直接的原因也越來越多！