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How Can I Remove This Extra Grid Space?

How can I stop this Grid from expanding vertically and adding all this extra space between the rows?
<ContentPage.Content>
<StackLayout>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Image Source="testsquare" />
<Image Source="testsquare" Grid.Column="1"/>
<Image Source="testsquare" Grid.Row="1"/>
<Image Source="testsquare" Grid.Column="1" Grid.Row="1"/>
</Grid>
</StackLayout>
</ContentPage.Content>
This is what it should look like (ignore the background color change)

Use "Auto" instead of "*"
<RowDefinition Height="Auto"/>

It appears to be a bug, where the grid height is being treated as if the image is being displayed at its full height.
<Grid BackgroundColor="CornflowerBlue">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="auto"/>
</Grid.RowDefinitions>
<Image Source="testsquare" />
<Image Source="testsquare" Grid.Column="1" />
</Grid>

There is a spacing property in Grid .
Grid has properties to control spacing between rows and columns. The following properties are available for customizing the Grid:
ColumnSpacing – the amount of space between columns. The default value of this property is 6.
RowSpacing – the amount of space between rows. The default value of this property is 6.
You can set RowSpacing or ColumnSpacing to check whether can solve it .
<StackLayout Padding="5">
<Grid RowSpacing="5" ColumnSpacing="5">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Image Source="icon.png" BackgroundColor="Accent"/>
<Image Source="icon.png"
BackgroundColor="Accent"
Grid.Column="1" />
<Image Source="icon.png"
BackgroundColor="Accent"
Grid.Row="1" />
<Image Source="icon.png"
BackgroundColor="Accent"
Grid.Column="1"
Grid.Row="1" />
</Grid>
</StackLayout>
About Image , The Aspect property determines how the image will be scaled to fit the display area, with Fill or AspectFill .(Default is AspectFit)

call objects inside of the controls from the codebehind Xamarin forms

how come I can not call the object image and the object image backClickArrow nextClickArrow from codebehind? They can not because these are inside a control?
how can I call from codebehind, they need to start an event? thank you so much.
<control:CarouselView x:Name="carouselView">
<control:CarouselView.ItemTemplate>
<DataTemplate>
<Grid Padding="10">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"></ColumnDefinition>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="40*"></RowDefinition>
<RowDefinition Height="0.2*"></RowDefinition>
<RowDefinition Height="59.8*"></RowDefinition>
</Grid.RowDefinitions>
<Grid Grid.Row="0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="5*"></ColumnDefinition>
<ColumnDefinition Width="40*"></ColumnDefinition>
<ColumnDefinition Width="50*"></ColumnDefinition>
<ColumnDefinition Width="5*"></ColumnDefinition>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
<Image Source="backBlueArrow.png" x:Name="backClickArrow" Aspect="AspectFit" Grid.Column="0"></Image>
<StackLayout Margin="0,0,10,0" VerticalOptions="Center" HorizontalOptions="End" Grid.Column="1">
<Image HeightRequest="70" Source="clock.png" Aspect="AspectFit"></Image>
</StackLayout>
<Grid Grid.Row="0" Grid.Column="2">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"></ColumnDefinition>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="40*"></RowDefinition>
<RowDefinition Height="60*"></RowDefinition>
</Grid.RowDefinitions>
<Label Text="Superficie totale" TextColor="#fff" FontSize="Small" VerticalTextAlignment="End" HorizontalTextAlignment="Start" Grid.Row="0"/>
<Label Text="890000m2" FontSize="Large" TextColor="#fff" VerticalTextAlignment="Start" HorizontalTextAlignment="Start" Grid.Row="1"/>
</Grid>
<Image Source="nextBlueArrow.png" x:Name="nextClickArrow" Aspect="AspectFit" Grid.Column="3"></Image>
</Grid>
<!-- griglia fare la riga bianca -->
<Grid Padding="0" BackgroundColor="White" Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"></ColumnDefinition>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
</Grid>
<Grid Padding="10" Grid.Row="2">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"></ColumnDefinition>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
</Grid>
</Grid>
<!--<Label Text="{Binding Testo}" />-->
</DataTemplate>
</control:CarouselView.ItemTemplate>
</control:CarouselView>
the object that i wish call:
<Image Source="backBlueArrow.png" x:Name="backClickArrow" Aspect="AspectFit" Grid.Column="0"></Image>
and
<Image Source="nextBlueArrow.png" x:Name="nextClickArrow" Aspect="AspectFit" Grid.Column="3"></Image>

i have solved like this:
<Button Image="nextBlueArrow.png" Clicked="clickme" Grid.Column="3"></Button>
use button and add Image attribute.

Custom xaml layout using RowDefinitions and ColumnDefinitions

I am new in UWP and I get some misunderstanding grid RowDefinitions and ColumnDefinitions as is mentioned in oficial doc. I have to make a custom list element, something like this:
but I can't handle it. In fact the main problem is how to set fill_parent property for a child view.

You can use this method like it's indicated in your mentioned docs. As is described in your img the last element it's in the middle vertically, so this layout will be:
<Grid>
<Grid.RowDefinitions>
<RowDefinition
Height="24" />
<RowDefinition
Height="20" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition
Width="44" />
<ColumnDefinition
Width="*" />
<ColumnDefinition
Width="10" />
</Grid.ColumnDefinitions>
<Rectangle
Fill="Red"
Grid.RowSpan="2"
Grid.Column="0"/>
<Rectangle
Fill="Green"
Grid.Row="0"
Grid.Column="1" />
<Rectangle
Fill="Yellow"
Grid.Row="1"
Grid.Column="1" />
<Grid
Grid.RowSpan="2"
Grid.Column="2">
<Grid.RowDefinitions>
<RowDefinition
Height="*" />
<RowDefinition
Height="*" />
<RowDefinition
Height="*" />
</Grid.RowDefinitions>
<Rectangle
Fill="Gray"
Grid.Row="1"/>
</Grid>
</Grid>
For simplicity and clarity I was using Rectangle

Filling the space can be done with
width="*"
And the small complexity in your layout could be handled with nested grid system.
Here is the beginning, not the complete solution for your layout.
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="44"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="44"/>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="10"/>
</Grid.ColumnDefinitions>
<Grid Grid.Row="0" Grid.Column="1">
<Grid.RowDefinitions>
<RowDefinition Height="24"/>
<RowDefinition Height="20"/>
</Grid.RowDefinitions>
</Grid>
</Grid>

Independent width in a WPF Grid

I have a grid with 2 rows and 2 columns in WPF. I would like that the column widths are independent for each row. I tried "auto", but no success. Here is a picture in order to explain:
How can I accomplish this using grid?

If you must use a grid layout, then you have a couple of options:
Option 1: Make each row a single column and then nest a grid in each row you would like independent columns:
XAML
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<TextBlock Text="AAAAAAAAAAAAAAAAAAAA" />
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<TextBlock Text="BBBBBBB"">
<TextBlock Grid.Column="1" Text="CCCCCCC" />
</Grid>
</Grid>
Option 2: Make use of ColumnSpan in the rows:
XAML
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<TextBlock Grid.ColumnSpan="2" Text="AAAAAAAAAAAAAAAAAAAA" />
<TextBlock Grid.Row="1" Text="BBBBBBB"">
<TextBlock Grid.Row="1" Grid.Column="1" Text="CCCCCCC" />
</Grid>
</Grid>
*These were typed without an editor and may need a bit of tweaking.

Two grids?
<StackPanel Width="277">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<TextBlock Text="AAAAAAAAAAAAAAAAAAAA" Grid.Row="0" Grid.Column="0"/>
</Grid>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<TextBlock Text="BBBBBBB" Grid.Row="0" Grid.Column="0"/>
<TextBlock Text="CCCCCCC" Grid.Row="0" Grid.Column="1"/>
</Grid>
</StackPanel>

How to add a control button for displaying data prev entered

I have a small screen program which displays patients at the top there is a search button where u can enter by name. I need this search display to be controlled by a button that is, it should not display any records (prev entered) unless click on this button, how would i set this up?
<Grid x:Name="LayoutRoot" Background="LightGray" >
<Grid.RowDefinitions>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"></ColumnDefinition>
<ColumnDefinition Width="*"></ColumnDefinition>
<ColumnDefinition Width="Auto"></ColumnDefinition>
<ColumnDefinition Width="*"></ColumnDefinition>
</Grid.ColumnDefinitions>
<Grid Grid.Row="0" Grid.Column="1" Grid.ColumnSpan="3">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"></ColumnDefinition>
<ColumnDefinition Width="*"></ColumnDefinition>
<ColumnDefinition Width="Auto"></ColumnDefinition>
<ColumnDefinition Width="*"></ColumnDefinition>
<ColumnDefinition Width="Auto"></ColumnDefinition>
<ColumnDefinition Width="*"></ColumnDefinition>
<ColumnDefinition Width="Auto" ></ColumnDefinition>
<ColumnDefinition Width="Auto" ></ColumnDefinition>
<ColumnDefinition Width="Auto" ></ColumnDefinition>
<ColumnDefinition Width="Auto" ></ColumnDefinition>
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0" Text="First Name:" Margin="3"></TextBlock>
<TextBox Grid.Column="1" x:Name="sTxtFirstName" Margin="3"></TextBox>
<TextBlock Grid.Column="2" Text="Last Name:" Margin="3"></TextBlock>
<TextBox Grid.Column="3" x:Name="sTxtLastName" Margin="3"></TextBox>
<TextBlock Grid.Column="4" Text="Gender:" Margin="3"></TextBlock>
<ComboBox Grid.Column="5" x:Name="sCombGender" Margin="3">
<ComboBoxItem Content=""></ComboBoxItem>
<ComboBoxItem Content="Male"></ComboBoxItem>
<ComboBoxItem Content="Female"></ComboBoxItem>
</ComboBox>
<Button x:Name="btnSearch" Grid.Column="6" Margin="3" Height="30" Command="{Binding CMDSearch}" >
<Button.Content>
<StackPanel Orientation="Horizontal">
<Image Source="/PBM;component/Resources/Images/search.png" VerticalAlignment="Center" Margin="0,0,2,0" ></Image>
<TextBlock Text="Search" Width="50" VerticalAlignment="Center" Margin="1,0,0,0"></TextBlock>
</StackPanel>
</Button.Content>
</Button>

You're going about it all wrong. Only use grid for laying out controls on the screen.
Use a ListBox to show a list of items.
Declare your items in an ObservableCollection.
Use data binding to bind the listbox to the observable collection.
Use C# to manipulate the contents of the list in response to your button click, then the list data appears automatically.