xamarin - 无法更改 Xamarin 表单代码中的标签文本

Question

我是 Xamarin Forms 的初学者。我使用 C# 代码添加标签和按钮控件。我希望点击按钮，它可以在应用程序上同时更改标签文本。但现在不能。我的部分代码如下。

 Label lblPanel = new Label ();
    public MainPage()
    {
        InitializeComponent();


        Grid grid = new Grid()
        {
            RowSpacing = 10,
            ColumnSpacing = 10
        };
        grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(2, GridUnitType.Star) });
        grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        grid.ColumnDefinitions.Add(new ColumnDefinition { });
        grid.ColumnDefinitions.Add(new ColumnDefinition { });
        grid.ColumnDefinitions.Add(new ColumnDefinition { });
        grid.ColumnDefinitions.Add(new ColumnDefinition { });

        Label lblPanel = new Label { Text = "0", FontSize = 50, HorizontalOptions = LayoutOptions.End, VerticalOptions = LayoutOptions.End };
        grid.Children.Add(lblPanel, 0, 0);
        Grid.SetColumnSpan(lblPanel, 4);
        Grid.SetRow(lblPanel, 0);

        var btn01 = new Button { Text = "1", BackgroundColor = Color.CadetBlue };
        btn01.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn01, 0, 0);
        Grid.SetRow(btn01, 4);
        Grid.SetColumn(btn01, 2);

        var btn02 = new Button { Text = "2", BackgroundColor = Color.CadetBlue };
        btn02.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn02, 0, 0);
        Grid.SetRow(btn02, 4);
        Grid.SetColumn(btn02, 1);

        var btn03 = new Button { Text = "3", BackgroundColor = Color.CadetBlue };
        btn03.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn03, 0, 0);
        Grid.SetRow(btn03, 4);
        Grid.SetColumn(btn03, 0);

        var btn04 = new Button { Text = "4", BackgroundColor = Color.CadetBlue };
        btn04.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn04, 0, 0);
        Grid.SetRow(btn04, 3);
        Grid.SetColumn(btn04, 2);

        var btn05 = new Button { Text = "5", BackgroundColor = Color.CadetBlue };
        btn05.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn05, 0, 0);
        Grid.SetRow(btn05, 3);
        Grid.SetColumn(btn05, 1);

        var btn06 = new Button { Text = "6", BackgroundColor = Color.CadetBlue };
        btn06.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn06, 0, 0);
        Grid.SetRow(btn06, 3);
        Grid.SetColumn(btn06, 0);

        var btn07 = new Button { Text = "7", BackgroundColor = Color.CadetBlue };
        btn07.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn07, 0, 0);
        Grid.SetRow(btn07, 2);
        Grid.SetColumn(btn07, 2);

        var btn08 = new Button { Text = "8", BackgroundColor = Color.CadetBlue };
        btn08.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn08, 0, 0);
        Grid.SetRow(btn08, 2);
        Grid.SetColumn(btn08, 1);

        var btn09 = new Button { Text = "9", BackgroundColor = Color.CadetBlue };
        btn09.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn09, 0, 0);
        Grid.SetRow(btn09, 2);
        Grid.SetColumn(btn09, 0);

        var btn0 = new Button { Text = "0", BackgroundColor = Color.CadetBlue };
        btn0.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btn0, 0, 0);
        Grid.SetColumnSpan(btn0, 3);
        Grid.SetRow(btn0, 5);

        var btnClear = new Button { Text = "C", BackgroundColor = Color.CadetBlue };
        btnClear.Clicked += (object sender, EventArgs e) =>
        {
            Clear_Click(sender, e);
        };
        grid.Children.Add(btnClear, 0, 0);
        Grid.SetRowSpan(btnClear, 2);
        Grid.SetRow(btnClear, 3);
        Grid.SetColumn(btnClear, 3);

        var btnEqual = new Button { Text = "=", BackgroundColor = Color.CadetBlue };
        btnEqual.Clicked += (object sender, EventArgs e) =>
        {
            Caculate_Click(sender, e);
        };
        grid.Children.Add(btnEqual, 0, 0);
        Grid.SetRow(btnEqual, 2);
        Grid.SetColumn(btnEqual, 3);

        var btnDivision = new Button { Text = "/", BackgroundColor = Color.CadetBlue };
        btnDivision.Clicked += (object sender, EventArgs e) =>
        {
            Caculate_Click(sender, e);
        };
        grid.Children.Add(btnDivision, 0, 0);
        Grid.SetRow(btnDivision, 1);
        Grid.SetColumn(btnDivision, 0);

        var btnTimes = new Button { Text = "*", BackgroundColor = Color.CadetBlue };
        btnTimes.Clicked += (object sender, EventArgs e) =>
        {
            Caculate_Click(sender, e);
        };
        grid.Children.Add(btnTimes, 0, 0);
        Grid.SetRow(btnTimes, 1);
        Grid.SetColumn(btnTimes, 1);

        var btnCut = new Button { Text = "-", BackgroundColor = Color.CadetBlue };
        btnCut.Clicked += (object sender, EventArgs e) =>
        {
            Caculate_Click(sender, e);
        };
        grid.Children.Add(btnCut, 0, 0);
        Grid.SetRow(btnCut, 1);
        Grid.SetColumn(btnCut, 2);

        var btnPlus = new Button { Text = "+", BackgroundColor = Color.CadetBlue };
        btnPlus.Clicked += (object sender, EventArgs e) =>
        {
            Caculate_Click(sender, e);
        };
        grid.Children.Add(btnPlus, 0, 0);
        Grid.SetRow(btnPlus, 1);
        Grid.SetColumn(btnPlus, 3);

        var btnDot = new Button { Text = ".", BackgroundColor = Color.CadetBlue };
        btnDot.Clicked += (object sender, EventArgs e) =>
        {
            BtnNumber_Click(sender, e);
        };
        grid.Children.Add(btnDot, 0, 0);
        Grid.SetRow(btnDot, 5);
        Grid.SetColumn(btnDot, 3);

        Content = grid;      
    }

和按钮点击事件。

    private void BtnNumber_Click(object sender, EventArgs e)
    {
        var numButton = (sender as Button);
        var keyInNumber = numButton.Text;
        if (lblPanel.Text == "0")
            lblPanel.Text = keyInNumber;
        else
            lblPanel.Text += keyInNumber;
    }

我可以看到 lblPanel.text 在调试模式下已更改，但在应用程序上没有更改。有人可以帮我吗？谢谢！

标签： xamarinxamarin.forms

Answer 1

您在构造函数的内部和外部定义了 lblPanel 两次，这使得内部的 MainPage 成为本地的，而 BtnNumber_Click 在全局的...

它应该像

public Label lblPanel; // <-- here you define it..
public MainPage() {
   ...
   // Here you assign it..
   lblPanel = new Label { Text = "0",...