如何使用 FluentLayout 设置视图高度

如何解决如何使用 FluentLayout 设置视图高度

我在 Xamarin.iOS 项目中使用 FluentLayout。我创建了一个视图：

public class SignInView : UIView
{
    private const int headerSpacing = 20;
    private const int textFieldSpacing = 10;
    private const int textFieldButtonSpacing = 15;
    private const int buttonSpacing = 10;
    private const int textFieldHeight = 50;

    public SignInView()
    {
        ConstructView();
    }

    private void ConstructView()
    {
        var signInLabel = new UILabel() { Text = "sign in" };
        var usernameTextField = new UITextField() { Placeholder = "enter username" };
        var passwordTextField = new UITextField() { Placeholder = "enter password" };
        var signInButton = new UIButton();
        var createAccountButton = new UIButton();

        signInButton.SetTitle("sign in",UIControlState.normal);
        createAccountButton.SetTitle("create account",UIControlState.normal);

        AddSubviews(signInLabel,usernameTextField,passwordTextField,signInButton,createAccountButton);

        this.SubviewsDoNottranslateAutoresizingMaskIntoConstraints();

        this.AddConstraints(
            signInLabel.WithSametop(this),signInLabel.WithSameCenterX(this),usernameTextField.Below(signInLabel,headerSpacing),usernameTextField.WithSameWidth(this),usernameTextField.Height().GreaterThanorEqualTo(textFieldHeight),passwordTextField.Below(usernameTextField,textFieldSpacing),passwordTextField.WithSameWidth(this),passwordTextField.Height().GreaterThanorEqualTo(textFieldHeight),signInButton.Below(passwordTextField,textFieldButtonSpacing),signInButton.WithSameWidth(this),createAccountButton.Below(signInButton,buttonSpacing),createAccountButton.WithSameWidth(this)
        );

        BackgroundColor = UIColor.Red;
    }
}

当我在视图中放置 SignInView 时，我可以正确地看到所有内容，但背景不是红色，因为高度为零，并且出于同样的原因，没有任何内容可点击。有没有办法将 SignInView 中的高度设置为 createAccountButton 的底部？

顺便说一下，SubviewsDoNottranslateAutoresizingMaskIntoConstraints 是做什么的？我总是需要它以便约束起作用，但不知道它究竟做了什么。

解决方法

我想出了一个技巧。我子类 UIButton 并放置一个事件处理程序来通知约束何时更新，以便我的 SignInView 可以使用适当的高度更新其约束。

public class ConstraintsButton : UIButton
{
    public event EventHandler ConstraintsUpdated;

    public override void UpdateConstraints()
    {
        base.UpdateConstraints();
        
        ConstraintsUpdated?.Invoke(null,EventArgs.Empty);
    }
}

public class SignInView : UIView
{
    private const int headerSpacing = 20;
    private const int textFieldSpacing = 10;
    private const int textFieldButtonSpacing = 15;
    private const int buttonSpacing = 10;
    private const int textFieldHeight = 50;
    private const int buttonHeight = 50;

    private ConstraintsButton _createAccountButton;
    private FluentLayout _heightConstraint;

    public SignInView()
    {
        ConstructView();
    }

    private void ConstructView()
    {
        var signInLabel = new UILabel() { Text = "sign in" };
        var usernameTextField = new UITextField() { Placeholder = "enter username" };
        var passwordTextField = new UITextField() { Placeholder = "enter password" };
        var signInButton = new UIButton();

        _createAccountButton = new ConstraintsButton();
        _createAccountButton.ConstraintsUpdated += CreateAccountButton_ConstraintsUpdated;

        signInButton.SetTitle("sign in",UIControlState.Normal);
        _createAccountButton.SetTitle("create account",UIControlState.Normal);

        AddSubviews(signInLabel,usernameTextField,passwordTextField,signInButton,_createAccountButton);

        this.SubviewsDoNotTranslateAutoresizingMaskIntoConstraints();

        this.AddConstraints(
            signInLabel.WithSameTop(this),signInLabel.WithSameCenterX(this),usernameTextField.Below(signInLabel,headerSpacing),usernameTextField.WithSameWidth(this),usernameTextField.Height().GreaterThanOrEqualTo(textFieldHeight),passwordTextField.Below(usernameTextField,textFieldSpacing),passwordTextField.WithSameWidth(this),passwordTextField.Height().GreaterThanOrEqualTo(textFieldHeight),signInButton.Below(passwordTextField,textFieldButtonSpacing),signInButton.WithSameWidth(this),signInButton.Height().EqualTo(buttonHeight),_createAccountButton.Below(signInButton,buttonSpacing),_createAccountButton.WithSameWidth(this),_createAccountButton.Height().EqualTo(buttonHeight)
        );

        BackgroundColor = UIColor.Red;
    }

    private void CreateAccountButton_ConstraintsUpdated(object sender,EventArgs e)
    {
        if (_heightConstraint != null)
        {
            this.RemoveConstraints(_heightConstraint);
        }

        _heightConstraint = this.Height().EqualTo(_createAccountButton.Frame.Bottom);

        this.AddConstraints(_heightConstraint);
    }
}