当 1 个或多个 TextBox 字段为空时禁用按钮

Question

I tried a few solution but they seems to be for WPF.

This is what I have for the moment but it doesn't seems to work:

<Grid>
    <StackPanel Orientation="Vertical">
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Username :"/>
            <TextBox x:Name="userNameTextBox" Text="{Binding Username, Mode=TwoWay}" />
        </StackPanel>
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Password :" />
            <TextBox x:Name="passwordTextBox" Text="{Binding Password, Mode=TwoWay}" />
        </StackPanel>
        <Button IsEnabled="{Binding ElementName=userNameTextBox, Path=Text.Length}" Command="{Binding LoginCommand }" Content="Login" />
    </StackPanel>
</Grid>

So I want to make the button enables if userNameTextBox and passwordTextBox are not empty.

It stays enabled all the time. What am I doing wrong? Is it possible to do this only via XAML?

private string _username;
public string Username
{
    get { return _username; }
    set
    {
        _username = value;
        RaisePropertyChanged(nameof(Username));
        RaisePropertyChanged(nameof(IsButtonEnable));
    }
}

private string _password;
public string Password
{
    get { return _password; }
    set {
        _password = value;
        RaisePropertyChanged(nameof(Password));
        RaisePropertyChanged(nameof(IsButtonEnable));
    }
}

private bool _isButtonEnable;
public bool IsButtonEnable
{            
    get
    {
        if (!string.IsNullOrEmpty(_username) && !string.IsNullOrWhiteSpace(_username)
            && !string.IsNullOrEmpty(_password) && !string.IsNullOrWhiteSpace(_password))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

Answer 1

I think you can set a boolean value to disable that button. Here is sample code given below=>
XAML:

<Grid>
    <StackPanel Orientation="Vertical">
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Username :"/>
            <TextBox x:Name="userNameTextBox" Text="{Binding Username, Mode=TwoWay}" />
        </StackPanel>
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Password :" />
            <TextBox x:Name="passwordTextBox" Text="{Binding Password, Mode=TwoWay}" />
        </StackPanel>
        <Button IsEnabled="{Binding IsButtonEnable}" Command="{Binding LoginCommand }" Content="Login" />
    </StackPanel>
</Grid>

In ViewModel Add IsButtonEnable Property Like

#region Property IsButtonEnable: bool
public bool IsButtonEnable
{
    get
    {
        if( !string.IsNullOrEmpty(_Username) && !string.IsNullOrWhiteSpace(_Username)
            && !string.IsNullOrEmpty(_Password) && !string.IsNullOrWhiteSpace(_Password))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

#endregion

#region Property Username: string
private string _Username;
public string Username
{
    get { return _Username; }
    set
    {
        _Username = value;
        NotifyPropertyChanged(nameof(Username));
        NotifyPropertyChanged(nameof(IsButtonEnable));
    }
}

#endregion

#region Property Password: string
private string _Password;
public string Password
{
    get { return _Password; }
    set
    {
        _Password = value;
        NotifyPropertyChanged(nameof(Password));
        NotifyPropertyChanged(nameof(IsButtonEnable));
    }
}

#endregion

Note: Here NotifyPropertyChanged will call IsButtonEnable to update UI when either Username or Password is changed. You want to add more property then add them and update if condition inside IsButtonEnable get section.
Please check and let me know.