I recently started playing with SwiftUI and though there are some good things too it, so far I am very disappointed. Especially by the fact that it makes it really easy to create large, messy looking code and reminds me of XML ( or HTML ) structure of sorts.
Anyhow, I am running into the following problem that I can't find a solution for anywhere.
I need to draw certain rectangles ( or shapes ) at run time, think about it as generating a horizontal bar-chart in a way. Because the number of rects is dynamic, I need to generate this in a method, however I am getting an error from the compiler with any method I've tried so far.
Whenever I try and use some sort of flow control, like 'for' or 'while' in order to generate elements inside the:
struct ContentView: View {
or :
var body: some View {
I either get:
Function declares an opaque return type, but has no return statements in its body from which to infer an underlying type
or
Closure containing control flow statement cannot be used with function builder 'ViewBuilder'
What would be a better approach for drawing dynamic elements with SwiftUI.
I've seen a ton of examples on dynamic lists, even though that was covered by Apple already on day 1, but nothing that would be about custom elements or if you wanted to create a dynamically set number of HStack or Vstack, that are not formatted as a List.
Thank you!
ViewBuilders are special things and you cannot use certain control flow statements in them.
You can call out to separate (private) functions to do the appropriate control flow and produce the appropriate views.
See this blog post by John Sundell on the Swift 5.1 features that power SwiftUI: https://www.swiftbysundell.com/articles/the-swift-51-features-that-power-swiftuis-api/
Related
I noticed that hyperHTML preserves references I make to elements:
let div = document.createElement("div");
div.textContent = "Before Update";
hyperHTML.bind(document.body)`static1 - ${div} - static2`;
div.textContent = "After Update";
Above will produce a page that says:
static1 - After Update - static2
It is my understanding that hyperHTML ultimately clones an HTML <tempate> element to render the final output. However, don't you typical lose references when cloning an HTML template (like the variable "div" in the example above)?
Therefore, on the initial render, does hyperHTML somehow replace cloned elements with their originals after cloning the HTML template?
Here's how I think it works:
Create an HTML Template of the original template literal while
replacing all interpolations with comments.
Clone the html template with comments left in.
Make elements or document fragments out of each interpolation originally recieved
Replace each comment in the clone with its processed interpolation.
Is this correct?
I am not sure what is the question here, but there is a documentation page, and various examples too to understand how to use hyperHTML, which is not exactly in the way you are using it.
In fact, there's no need to have any reference there because hyperHTML is declarative, so you'd rather write:
function update(text) {
var render = hyperHTML.bind(document.body);
render`static1 - <div>${text}</div> - static2`;
}
and call update("any text") any time you need.
Here's how I think it works ... Is this correct?
No, it's not. hyperHTML doesn't clone anything the way you described, it associates once per unique template tag a sanitized version to the output and finds out all interpolated holes in it.
The part of the library that does this is called domtagger, and the mapping per template literal is based on the standard fact that these are unique per scope:
const templates = [];
function addTemplate(template, value) {
templates.push(template);
return template.join(value);
}
function asTemplate(value) {
return addTemplate`number ${value}!`;
}
asTemplate(1);
asTemplate(2);
asTemplate(Math.random());
templates[0] === templates[1]; // true
templates[1] === templates[2]; // true
// it is always the same template object!
After that, any other element using once that very same tag template will have a clone of that fragment with a map to find holes once and some complex logic to avoid replacing anything that's already known, being that text, attributes, events, or any other kind of node.
hyperHTML never removes comments, it uses these as pin and then uses domdiff to eventually update nodes related to these pins whenever there's a need to update anything.
Domdiff is a vDOM-less implementation of the petit-dom algorithm, which in turns is based on E.W Myers' "An O(ND) Difference Algorithm and Its Variations" paper.
Whenever you have DOM nodes in the holes, hyperHTML understand that and fill these holes with those nodes. If you pass repeatedly the same node, hyperHTML won't do anything 'cause it's full of algorithm and smart decisions, all described in the documentation, to obtain best performance out of its abstraction.
All these things, and much more, normalized for any browser out there, makes hyperHTML weight roughly 7K once minified and gzipped, bit it also offers:
Custom Elements like hooks through onconnected/disconnected listeners
lightweight components through hyperHTML.Component
SVG manipulation as content or via wire
easy Custom Elements definition through HyperHTMLElement class
As summary, if you need these simplifications and you don't want to reinvent the wheel, I suggest you give it a better try.
If you instead are just trying to understand how it works, there's no need to assume anything because the project is fully open source.
So far, all I've read from your questions here and there, is that you just believe to understand how it works so I hope in this reply I've put together all the missing pieces you need to fully understand it.
Do you want to write your own lit/hyperHTML library? Go ahead, feel free to use the domtagger or the domdiff library too, few others are already doing the same.
I'm trying to use layers to make sure I separate everything into it's correct areas in my Swift / iOS / Xcode 6 project. The question, ultimately, is: is it OK / a common practice to move commonly used presentation-level logic to a separate presentation helper class instead of writing it over and over in multiple view controllers with little or no difference?
Here is an example to tie this in and give context:
One of the things I am aiming to do is use a UITableView to display report data. This UITableView will contain 7-10 rows, depending upon the user's preferences (nsuserdefaults). Each row contains a localized string for a label, and some decimal value.
As an example one row could be "Sales made this week: $500.00"
I have a reporting service class that's responsible for talking to the database and getting back / instantiating a report object. This report object contains the raw data for the report, i.e. how much you made this week, this month, this year, etc. Whether the user wants to show all these values or not is irrelevant to the service - it simply gets everything.
So since I have 3 view models that use this same report, I thought it would be wrong to rewrite the same code each time that checks the user's preferences, then creates/binds an array to the UITable and matches the labels with the report values from the object returned by the service.
A better way, I thought, was to create a presentation-level helper class whose job would be to take a report object (the thing I mentioned before that contains the report values), take a user's preferences, and then more generically combine them to create a list of localized strings matched with their respective report values, agnostic to what the view controller wants. Maybe if that requirement changes later (where different view controllers need more customization) I could use flags or different function names within that class.
This way all I have to do is something like
var report = ReportHelper.GenerateReport(reportData, userSettings)
and now report would be an object that could look like this (mock JSON data):
{"Amount made this week":"$100", "Amount made this month":"$500", "Amount made this year": "$10,000"}
And I can use this in any view controller.
The alternate is to just hard code those above values (obviously still pulling localized strings) but I don't know if I adding all those strings + checks based on user preferences + formatting. Seems more elegant to move it away.
Thanks!
I know too little about your problem to provide the definite answer, but basically you have 2 options:
- inheritance
- composition
I personally like inheritance although it is often stated you should choose composition over inheritance.
Your helper sounds somewhat like composition, so that would be the preferred setup. With your specific problem as I understand it, inheritance would lead to a duplication of data, so that is one more argument to choose composition.
So all in all you seem to be about right
Edit:
Inheritance is an "is" relationship, whereas composition is a "has" relationship.
See http://en.wikipedia.org/wiki/Object_composition for more details about composition.
And see http://en.wikipedia.org/wiki/Composition_over_inheritance for more info why and when to choose composition
I'm doing some competitions on a website called topcoder.com where the objective is to solve algorithmic problems. I'm using Eclipse for this purpose, and I code in Java, it would be help me to have some predefined templates or macros that I can use for common coding tasks. For example I would like to write methods to be able to find the max value in and int[] array, or the longest sequence in an int[] array, and so on (there should be quite many of these). Note I can't write these methods as libraries because as part of the competition I need to submit everything in one file.
Therefore ideally, I would like to have some shortcut available to generate code both as a method and as a calling statement at once. Any ideas if this is possible?
Sure you can - I think that's a nifty way to auto-insert boilerplate or helper code. To the point of commenters, you probably want to group the code as a helper class, but the general idea sounds good to me:
You can see it listed in your available templates:
Then as you code your solution, you can Control+Space, type the first few characters of the name you gave your template, and you can preview it:
And then you can insert it. Be sure if you use a class structure to position it as an inner class:
Lastly - if you want to have a template inserts a call to method from a template, I think you would just use two templates. One like shown above (to print the helper code) and another that might look like this, which calls a util method and drops the cursor after it (or between the parentheses if you'd like, etc):
MyUtils.myUtilMethod1();${cursor}
I'm interested in approaches that avoids code in the code behind.
In my opinion, there are some cases where code must be placed in the code behind.
For example: I have a grid with an undefined count of columns. Columns can't be binded. So the easiest way would be to generate the columns in the code behind.
For this case, I can create a new class which inherits from the grid. This new class has a new binding property and code for the column binding. The code is separated in a custom class which can be used in the XAML. And then, I can easy bind the columns to my newly created property. And the view has no code behind.
Is it a good idea? How would you solve such (or similar) problems?
Are there other ways to extract the code from the code behind?
Thanks.
Having a code behind free xaml.cs and moving to code to a new class does not mean its pure MVVM. The idea is you will have all the logic in ViewModel hence a code behind free View, helping in Unit Testing. View specific logic like colors and animation cannot be unittested hence doesnt matter where it resides, in an custom control or a inherited control or directly in xaml.cs. As long as you are testing most of the user interactions and view logic via UnitTesting, you should be happy that you have done a good job.
Do you use table-of-contents for listing all the functions (and maybe variables) of a class in the beginning of big source code file? I know that alternative to that kind of listing would be to split up big files into smaller classes/files, so that their class declaration would be self-explanatory enough.. but some complex tasks require a lot of code. I'm not sure is it really worth it spending your time subdividing implementation into multiple of files? Or is it ok to create an index-listing additionally to the class/interface declaration?
EDIT:
To better illustrate how I use table-of-contents this is an example from my hobby project. It's actually not listing functions, but code blocks inside a function.. but you can probably get the idea anyway..
/*
CONTENTS
Order_mouse_from_to_points
Lines_intersecting_with_upper_point
Lines_intersecting_with_both_points
Lines_not_intersecting
Lines_intersecting_bottom_points
Update_intersection_range_indices
Rough_method
Normal_method
First_selected_item
Last_selected_item
Other_selected_item
*/
void SelectionManager::FindSelection()
{
// Order_mouse_from_to_points
...
// Lines_intersecting_with_upper_point
...
// Lines_intersecting_with_both_points
...
// Lines_not_intersecting
...
// Lines_intersecting_bottom_points
...
// Update_intersection_range_indices
for(...)
{
// Rough_method
....
// Normal_method
if(...)
{
// First_selected_item
...
// Last_selected_item
...
// Other_selected_item
...
}
}
}
Notice that index-items don't have spaces. Because of this I can click on one them and press F4 to jump to the item-usage, and F2 to jump back (simple visual studio find-next/prevous-shortcuts).
EDIT:
Another alternative solution to this indexing is using collapsed c# regions. You can configure visual studio to show only region names and hide all the code. Of course keyboard support for that source code navigation is pretty cumbersome...
I know that alternative to that kind of listing would be to split up big files into smaller classes/files, so that their class declaration would be self-explanatory enough.
Correct.
but some complex tasks require a lot of code
Incorrect. While a "lot" of code be required, long runs of code (over 25 lines) are a really bad idea.
actually not listing functions, but code blocks inside a function
Worse. A function that needs a table of contents must be decomposed into smaller functions.
I'm not sure is it really worth it spending your time subdividing implementation into multiple of files?
It is absolutely mandatory that you split things into smaller files. The folks that maintain, adapt and reuse your code need all the help they can get.
is it ok to create an index-listing additionally to the class/interface declaration?
No.
If you have to resort to this kind of trick, it's too big.
Also, many languages have tools to generate API docs from the code. Java, Python, C, C++ have documentation tools. Even with Javadoc, epydoc or Doxygen you still have to design things so that they are broken into intellectually manageable pieces.
Make things simpler.
Use a tool to create an index.
If you create a big index you'll have to maintain it as you change your code. Most modern IDEs create list of class members anyway. it seems like a waste of time to create such index.
I would never ever do this sort of busy-work in my code. The most I would do manually is insert a few lines at the top of the file/class explaining what this module did and how it is intended to be used.
If a list of methods and their interfaces would be useful, I generate them automatically, through a tool such as Doxygen.
I've done things like this. Not whole tables of contents, but a similar principle -- just ad-hoc links between comments and the exact piece of code in question. Also to link pieces of code that make the same simplifying assumptions that I suspect may need fixing up later.
You can use Visual Studio's task list to get a listing of certain types of comment. The format of the comments can be configured in Tools|Options, Environment\Task List. This isn't something I ended up using myself but it looks like it might help with navigating the code if you use this system a lot.
If you can split your method like that, you should probably write more methods. After this is done, you can use an IDE to give you the static call stack from the initial method.
EDIT: You can use Eclipse's 'Show Call Hierarchy' feature while programming.