Xamarin 4.2 Download


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  3. Xamarin.forms 5.0

Aug 21, 2019 The 4.2.0 release includes some bug fixes as well as fuller functionality including grouping on iOS. Update to Xamarin.Forms 4.2 Today. For full details about Xamarin.Forms 4.2.0, check the release notes. You can update your existing projects via the NuGet Package Manager. As always, feedback is very welcome.

  1. May 28, 2020 Xamarin can be installed as part of a new Visual Studio 2019 installation, with the following steps: Download Visual Studio 2019 Community, Visual Studio Professional, or Visual Studio Enterprise from the Visual Studio page (download links are provided at the bottom). Double-click the downloaded package to start installation.
  2. 3.1.0- May 9, 2018. New in this release: This is the first General Availability release for the Kinvey.NET SDK. This version includes a change to the PCL Profile used by the Kinvey.Core, which will affect both Xamarin and.NET SDK versions. The PCL profile used in 3.0.x versions of the SDK was PCL 4.5 - Profile 78, which has now changed to PCL.
  3. Microsoft RMS SDK 4.2 for iOS is a lightweight SDK for creating rights-enabled applications. By downloading the software, you agree to the license terms provided for this software.

After upgrading our Xamarin Forms project from VS 2017 (Xamarin Forms to VS 2019 (Xamarin Forms during stress and performance testing we noticed significant performance degradation when downloading files from ASP.NET (ASMX) web service. This is happening for Android and iOS but the problem is especially severe for Android.
For Android project we tried to set:
HTTPClient Implementation build option to Android,
SSL/TLS Implementation build option to Native TLS 1.2+
but it didn't improve performance by much.

Testing procedure:
Our Xamarin Forms app sequentially downloads 150 files ( each files size is roughly 1 MB) from ASP.NET (ASMX) web service.
The results of our testing:
App built with VS 2019 (Xamarin Forms is 35-45% slower then app built with VS 2017 (Xamarin Forms
App built with VS 2019 (Xamarin Forms is 10-20% slower then app built with VS 2017 (Xamarin Forms

We tried different IIS Authentication methods (Basic, Digest, Windows) and web service binding protocols (HTTP and HTTPS) but that didn't improve performance.

This is very serious issue for us and it is important to improve performance at least to the level of VS 2017 (Xamarin Forms build.

Any help or suggestions or workarounds will be greatly appreciated.

Thanks for help,


Steps to Reproduce

Expected Behavior

Actual Behavior

Basic Information

  • Version with issue:
  • Last known good version:
  • IDE: Microsoft Visual Studio Enterprise 2019 Version 16.5.4
  • Platform Target Frameworks:
    • iOS: 10.3
    • Android: 10.0
    • UWP: 18362
  • Android Support Library Version:
  • Nuget Packages: Xamarin.Essentials, SyncFusion, Symbol.XamarinEMDK, SkiaSharp, Rg.Plugins.Popup, ZXing.Net.Mobile.Forms, Microsoft.Data.Sqlite, MathParser.org-mXparser
  • Affected Devices: All


Reproduction Link


Today we’re excited to announce the release of TypeScript 4.2!

For those who aren’t familiar with TypeScript, it’s an extension to JavaScript that adds static types and type-checking. With types, you can state exactly what your functions take, and what they’ll return. You can then use the TypeScript type-checker to catch lots of common mistakes like typos, forgetting to handle null and undefined, and more. Because TypeScript code just looks like JavaScript with types, everything you know about JavaScript still applies. When you need, your types can be stripped out, leaving you with clean, readable, runnable JavaScript that works anywhere. To learn more about TypeScript, you can visit our website.

Xamarin 4.2 Download

To get started using TypeScript 4.2, you can get it through NuGet, or use npm with the following command:

You can also get editor support by

  • Installing the Insiders Version of Visual Studio Code or following directions to use a newer version of TypeScript
  • Sublime Text 3 via Package Control.

Let’s take a look at what’s in store for TypeScript 4.2!

Smarter Type Alias Preservation

TypeScript has a way to declare new names for types called type aliases. If you’re writing a set of functions that all work on string number boolean, you can write a type alias to avoid repeating yourself over and over again.

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TypeScript has always used a set of rules and guesses for when to reuse type aliases when printing out types. For example, take the following code snippet.

If we hover our mouse over x in an editor like Visual Studio, Visual Studio Code, or the TypeScript Playground, we’ll get a quick info panel that shows the type BasicPrimitive. Likewise, if we get the declaration file output (.d.ts output) for this file, TypeScript will say that doStuff returns BasicPrimitive.


However, what happens if we return a BasicPrimitive or undefined?

We can see what happens in the TypeScript playground. While we might want TypeScript to display the return type of doStuff as BasicPrimitive undefined, it instead displays string number boolean undefined! What gives?

Well this has to do with how TypeScript represents types internally. When creating a union type out of one or more union types, it will always normalize those types into a new flattened union type – but doing that loses information. The type-checker would have to find every combination of types from string number boolean undefined to see what type aliases could have been used, and even then, there might be multiple type aliases to string number boolean.

In TypeScript 4.2, our internals are a little smarter. We keep track of how types were constructed by keeping around parts of how they were originally written and constructed over time. We also keep track of, and differentiate, type aliases to instances of other aliases!

Being able to print back the types based on how you used them in your code means that as a TypeScript user, you can avoid some unfortunately humongous types getting displayed, and that often translates to getting better .d.ts file output, error messages, and in-editor type displays in quick info and signature help. This can help TypeScript feel a little bit more approachable for newcomers.

For more information, check out the first pull request that improves various cases around preserving union type aliases, along with a second pull request that preserves indirect aliases.

Leading/Middle Rest Elements in Tuple Types

In TypeScript, tuple types are meant to model arrays with specific lengths and element types.

Over time, TypeScript’s tuple types have become more and more sophisticated, since they’re also used to model things like parameter lists in JavaScript. As a result, they can have optional elements and rest elements, and can even have labels for tooling and readability.

In TypeScript 4.2, rest elements specifically been expanded in how they can be used. In prior versions, TypeScript only allowed ...rest elements at the very last position of a tuple type.

However, now rest elements can occur anywhere within a tuple – with only a few restrictions.

The only restriction is that a rest element can be placed anywhere in a tuple, so long as it’s not followed by another optional element or rest element. In other words, only one rest element per tuple, and no optional elements after rest elements.

These non-trailing rest elements can be used to model functions that take any number of leading arguments, followed by a few fixed ones.

Even though JavaScript doesn’t have any syntax to model leading rest parameters, we were still able to declare doStuff as a function that takes leading arguments by declaring the ...args rest parameter with a tuple type that uses a leading rest element. This can help model lots of existing JavaScript out there!

For more details, see the original pull request.

Stricter Checks For The in Operator

In JavaScript, it is a runtime error to use a non-object type on the right side of the in operator. TypeScript 4.2 ensures this can be caught at design-time.

This check is fairly conservative for the most part, so if you have received an error about this, it is likely an issue in the code.

Xamarin 4.2 download free

A big thanks to our external contributor Jonas Hübotter for their pull request!


Back when TypeScript first introduced index signatures, you could only get properties declared by them with “bracketed” element access syntax like person['name'].

This ended up being cumbersome in situations where we need to work with objects that have arbitrary properties. For example, imagine an API where it’s common to misspell a property name by adding an extra s character at the end.

To make these types of situations easier, a while back, TypeScript made it possible to use “dotted” property access syntax like person.name when a type had a string index signature. This also made it easier to transition existing JavaScript code over to TypeScript.

However, loosening the restriction also meant that misspelling an explicitly declared property became much easier.

In some cases, users would prefer to explicitly opt into the index signature – they would prefer to get an error message when a dotted property access doesn’t correspond to a specific property declaration.

That’s why TypeScript introduces a new flag called --noPropertyAccessFromIndexSignature. Under this mode, you’ll be opted in to TypeScript’s older behavior that issues an error. This new setting is not under the strict family of flags, since we believe users will find it more useful on certain codebases than others.

You can understand this feature in more detail by reading up on the corresponding pull request. We’d also like to extend a big thanks to Wenlu Wang who sent us this pull request!

abstract Construct Signatures

TypeScript allows us to mark a class as abstract. This tells TypeScript that the class is only meant to be extended from, and that certain members need to be filled in by any subclass to actually create an instance.

To make sure this restriction in new-ing up abstract classes is consistently applied, you can’t assign an abstract class to anything that expects a construct signature.

This does the right thing in case we intend to run code like new Ctor, but it’s overly-restrictive in case we want to write a subclass of Ctor.

It also doesn’t work well with built-in helper types like InstanceType.

That’s why TypeScript 4.2 allows you to specify an abstract modifier on constructor signatures.

Adding the abstract modifier to a construct signature signals that you can pass in abstract constructors. It doesn’t stop you from passing in other classes/constructor functions that are “concrete” – it really just signals that there’s no intent to run the constructor directly, so it’s safe to pass in either class type.

This feature allows us to write mixin factories in a way that supports abstract classes. For example, in the following code snippet, we’re able to use the mixin function withStyles with the abstract class SuperClass.

Note that withStyles is demonstrating a specific rule, where a class (like StyledClass) that extends a value that’s generic and bounded by an abstract constructor (like Ctor) has to also be declared abstract. This is because there’s no way to know if a class with more abstract members was passed in, and so it’s impossible to know whether the subclass implements all the abstract members.

You can read up more on abstract construct signatures on its pull request.

Understanding Your Project Structure With --explainFiles

A surprisingly common scenario for TypeScript users is to ask “why is TypeScript including this file?”. Inferring the files of your program turns out to be a complicated process, and so there are lots of reasons why a specific combination of lib.d.ts got used, why certain files in node_modules are getting included, and why certain files are being included even though we thought specifying exclude would keep them out.

That’s why TypeScript now provides an --explainFiles flag.

When using this option, the TypeScript compiler will give some very verbose output about why a file ended up in your program. To read it more easily, you can forward the output to a file, or pipe it to a program that can easily view it.

Typically, the output will start out by listing out reasons for including lib.d.ts files, then for local files, and then node_modules files.

Right now, we make no guarantees about the output format – it might change over time. On that note, we’re interested in improving this format if you have any suggestions!

For more information, check out the original pull request!

Improved Uncalled Function Checks in Logical Expressions


Thanks to further improvements from Alex Tarasyuk, TypeScript’s uncalled function checks now apply within && and expressions.

Under --strictNullChecks, the following code will now error.

For more details, check out the pull request here.

Destructured Variables Can Be Explicitly Marked as Unused

Thanks to another pull request from Alex Tarasyuk, you can now mark destructured variables as unused by prefixing them with an underscore (the _ character).

Previously, if _first was never used later on, TypeScript would issue an error under noUnusedLocals. Now, TypeScript will recognize that _first was intentionally named with an underscore because there was no intent to use it.

For more details, take a look at the full change.

Relaxed Rules Between Optional Properties and String Index Signatures

String index signatures are a way of typing dictionary-like objects, where you want to allow access with arbitrary keys:

Of course, for any movie title not yet in the dictionary, movieWatchCount[title] will be undefined (TypeScript 4.1 added the option --noUncheckedIndexedAccess to include undefined when reading from an index signature like this). Even though it’s clear that there must be some strings not present in movieWatchCount, previous versions of TypeScript treated optional object properties as unassignable to otherwise compatible index signatures, due to the presence of undefined.

TypeScript 4.2 allows this assignment. However, it does not allow the assignment of non-optional properties with undefined in their types, nor does it allow writing undefined to a specific key:

The new rule also does not apply to number index signatures, since they are assumed to be array-like and dense:

You can get a better sense of this change by reading up on the original PR.


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Declare Missing Helper Function

Thanks to a community pull request from Alexander Tarasyuk, we now have a quick fix for declaring new functions and methods based on the call-site!

Breaking Changes

We always strive to minimize breaking changes in a release. TypeScript 4.2 contains some breaking changes, but we believe they should be manageable in an upgrade.

lib.d.ts Updates

As with every TypeScript version, declarations for lib.d.ts (especially the declarations generated for web contexts), have changed. There are various changes, though Intl and ResizeObserver‘s may end up being the most disruptive.

noImplicitAny Errors Apply to Loose yield Expressions

When the value of a yield expression is captured, but TypeScript can’t immediately figure out what type you intend for it to receive (i.e. the yield expression isn’t contextually typed), TypeScript will now issue an implicit any error.

See more details in the corresponding changes.

Expanded Uncalled Function Checks

As described above, uncalled function checks will now operate consistently within && and expressions when using --strictNullChecks. This can be a source of new breaks, but is typically an indication of a logic error in existing code.

Type Arguments in JavaScript Are Not Parsed as Type Arguments

Type arguments were already not allowed in JavaScript, but in TypeScript 4.2, the parser will parse them in a more spec-compliant way. So when writing the following code in a JavaScript file:

TypeScript will parse it as the following JavaScript:

This may impact you if you were leveraging TypeScript’s API to parse type constructs in JavaScript files, which may have occurred when trying to parse Flow files.

The in Operator No Longer Allows Primitive Types on the Right Side

As mentioned, it is an error to use a primitive on the right side of an in operator, and TypeScript 4.2 is stricter about this sort of code.

See the pull request for more details on what’s checked.

Tuple size limits for spreads

Tuple types can be made by using any sort of spread syntax (...) in TypeScript.

Sometimes these tuple types can accidentally grow to be huge, and that can make type-checking take a long time. Instead of letting the type-checking process hang (which is especially bad in editor scenarios), TypeScript has a limiter in place to avoid doing all that work.

You can see this pull request for more details.

.d.ts Extensions Cannot Be Used In Import Paths

In TypeScript 4.2, it is now an error for your import paths to contain .d.ts in the extension.

Instead, your import paths should reflect whatever your loader will do at runtime. Any of the following imports might be usable instead.

Reverting Template Literal Inference

This change removed a feature from TypeScript 4.2 beta. If you haven’t yet upgraded past our last stable release, you won’t be affected, but you may still be interested in the change.

The beta version of TypeScript 4.2 included a change in inference to template strings. In this change, template string literals would either be given template string types or simplify to multiple string literal types. These types would then widen to string when assigning to mutable variables.

This is similar to how string literal inference works.

For that reason, we believed that making template string expressions have template string types would be “consistent”; however, from what we’ve seen and heard, that isn’t always desirable.

In response, we’ve reverted this feature (and potential breaking change). If you do want a template string expression to be given a literal-like type, you can always add as const to the end of it.

TypeScript’s lift Callback in visitNode Uses a Different Type

TypeScript has a visitNode function that takes a lift function. lift now expects a readonly Node[] instead of a NodeArray<Node>. This is technically an API breaking change which you can read more on here.

What’s Next?

While 4.2 was just released, our team is already hard at work on TypeScript 4.3. You can take a look at the TypeScript 4.3 iteration plan and our rolling feature roadmap to keep track of what we’re working on.

You can also stay on the bleeding edge with TypeScript nightly releases too, and with our nightly Visual Studio Code extension. Nightly releases tend to be fairly stable, and early feedback is encouraged and appreciated!

But we expect most users will stick with TypeScript 4.2 for now; and so if you are using TypeScript 4.2, we hope this release is easy to adopt and makes you a lot more productive. If not, we want to hear about it! We want to make sure that TypeScript brings you joy in your coding, and we hope we’ve done exactly that.

Happy Hacking!

Xamarin.forms 5.0

– Daniel Rosenwasser and the TypeScript Team