如何使用Device.OnPlatform翻译此填充？ （iOS案例）

Question

So Im working myself trough a xamarin.forms book right now and I came across this:

 Padding = new Thickness(5, Device.OnPlatform(20, 5, 5), 5, 5);

Device.OnPlatform get´sa warning that it is obsolete.

I know that I could translate

Padding = Device.OnPlatform(new Thickness(0,20,0,0),
new Thickness(0),
new Thickness(0));

to

        switch (Device.RuntimePlatform)
        {
            case Device.iOS:
                Padding = new Thickness(0, 20, 0, 0);
                break;
        };

But what exactly happens here and how do I translate this?

Padding = new Thickness(5, Device.OnPlatform(20, 5, 5), 5, 5);

Answer 1

The new Thickness(5, 5, 5, 5); with 4 double parameters means that it will create a new padding (in this case) with 5 on the left, 5 on the top, 5 on the right and 5 on the bottom. So, from left to right, you just go clockwise and start from the left.

We see that the second parameter (so the top padding) will be different depending on the platform. From the top of my head, I am not sure what parameter is what platform, but I'm guessing the first one will be iOS. What happens now, is that the left will have a padding of 5 and the top padding will be different per platform. For iOS, it will be 20 and for Android and UWP (remember, just a guess) it will still be 5. Then the right and bottom padding didn't change, so they are still 5 as well.

If you want to do it strictly in code, it might translate to something like this:

double topPadding = 5;

switch (Device.RuntimePlatform)
{
    case Device.iOS:
        topPadding = 20;
        break;
    default:
        topPadding = 5;
        break;
};

Padding = new Thickness(5, topPadding, 5, 5);

Of course, you can add some different cases or change the values, totally up to you.

You can also do it with XAML. It could then look like this:

<YourControl Padding="{OnPlatform '5,5,5,5', iOS='5,20,5,5'}" />

YourControl is the control you want to apply this on. The first '5,5,5,5' value after OnPlatform is a default value for all platforms not specified. The iOS is specified and will thus use the value specified for it. Read more on the OnPlatform extension here: https://docs.microsoft.com/en-us/xamarin/xamarin-forms/xaml/markup-extensions/consuming#onplatform-markup-extension