MultiTrigger.xaml

<?xml version="1.0" encoding="utf-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             xmlns:local="clr-namespace:DataTriggersFormsSample" 
             x:Class="DataTriggersFormsSample.MainPage">
    <StackLayout VerticalOptions="StartAndExpand"
                 Padding="20,60,20,20">

       <Entry x:Name="user" 
              Text="" 
              Placeholder="user name" />

        <Entry x:Name="password" 
              Text="" 
              Placeholder="user name"
              IsPassword="true" />
        
        <Button Text="Enter"
                BackgroundColor="LightSeaGreen"
                TextColor="White"
                IsEnabled="false">
              <Button.Triggers>
                <MultiTrigger TargetType="Button">
                  <MultiTrigger.Conditions>
                    <BindingCondition Binding="{Binding Source={x:Reference user},
                                      Path=Text}"
                                      Value="Char" />
                     <BindingCondition Binding="{Binding Source={x:Reference password},
                                      Path=Text}"
                                      Value="1234" />
                  </MultiTrigger.Conditions>
                  <Setter Property="IsEnabled" Value="true" />
                </MultiTrigger>
              </Button.Triggers>
       </Button>
    </StackLayout>
</ContentPage>