Connect and share knowledge within a single location that is structured and easy to search. How can I declare template class adaptor with different containers as template arguments? For example, I need to declare class:. And I want it to my based on vector. How to make it hard-defined? Here is a compiling live example. An alternative way of writing the above could be:. The only thing you have to pay attention to is that the number and type of arguments in the template template parameter declaration must match exactly the number and type of arguments in the definition of the corresponding class template you want to pass as a template argument, regardless of the fact that some of those parameters may have default values.
Because of this, you could not write:. This means that you won't be able to write one single class template that can accept both std::set and std::vector as a template template parameter, because unlike std::vector , the std::set class template accepts three template parameters. Another approach to solve this is by using variadic templates and with that you can use any container as suggested in comments above and here is the implemenation :.
If you look at the definitions of list and vector from cplusplus. So this should go as the type of the container, the other template parameter is the type of the elements. As an example this program will output 3 :. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Containers are used to pad the content inside of them, and there are two container classes available:. Use the. Note that its width max-width will change on different screen sizes:.
Open the example below and resize the browser window to see that the container width will change at different breakpoints:. By default, containers have 15px left and right padding, with no top or bottom padding. Therefore, we often use spacing utilities , such as extra padding and margins to make them look even better. For example,. You will learn much more about spacing utilities, in our BS4 Utilities Chapter. Here is how that would look like, we would start by defining the custom template for the buttons in the parent component:.
And then on the tab container component, we could define an input property which is also a template named headerTemplate :. The end result of this design is that the tab container will display a default look and feel for the tab buttons if no custom template is provided, but it will use the custom template if its available.
The core directives ng-container, ng-template and ngTemplateOutlet all combine together to allow us to create highly dynamical and customizable components. We can even change completely the look and feel of a component based on input templates , and we can define a template and instantiate on multiple places of the application. I hope that this post helped to get familiar with some of the more advanced features of Angular core, if you have some questions please let me know in the comments below and I will get back to you.
And if you would like to know about more advanced Angular Core features, we recommend checking the Angular Core Deep Dive course, where Angular Templates are covered in much more detail. If you are just getting started learning Angular, have a look at the Angular for Beginners Course :.
Table Of Contents In this post, we will be going over the following topics: Introduction to the ng-template directive Template Input Variables The ng-template directive use with ngIf ngIf de-suggared syntax and ng-template ng-template template references and the TemplateRef injectable Configurable Components with Template Partial Inputs The ng-container directive, when to use it?
Dynamic Template with the ngTemplateOutlet custom directive Template outlet Input Properties Final Combined Example Summary and Conclusions Introduction to the ng-template directive Like the name indicates, the ng-template directive represents an Angular template: this means that the content of this tag will contain part of a template, that can be then be composed together with other templates in order to form the final component template.
Here we are defining two tab buttons of a tab component more on this later : The first thing that you will notice about ng-template If you try the example above, you might be surprised to find out that this example does not render anything to the screen!
But based on this example, one question might come to mind: How does this work if there are multiple structural directives applied to the same element? Multiple Structural Directives Let's see what happens if for example we try to use ngIf and ngFor in the same element: This would not work! Instead, we would get the following error message: Uncaught Error: Template parse errors: Can't have multiple template bindings on one element.
In order to do so, we would have to do something similar to this: In this example, we have moved the ngIf directive to an outer wrapping div, but in order for this to work we have to create that extra div element. Yes and that is exactly what the ng-container structural directive allows us to do! The ng-container directive In order to avoid having to create that extra div, we can instead use ng-container directive: As we can see, the ng-container directive provides us with an element that we can attach a structural directive to a section of the page, without having to create an extra element just for that.
Dynamic Template Creation with the ngTemplateOutlet directive Being able to create template references and point them to other directives such as ngIf is just the beginning. We can also take the template itself and instantiate it anywhere on the page, using the ngTemplateOutlet directive: We can see here how ng-container helps with this use case: we are using it to instantiate on the page the loading template that we defined above.
Template Context One key question about templates is, what is visible inside them? Does the template have its own separate variable scope, what variables can the template see? Let's have a look at an example: Here is the breakdown of this example: this template, unlike the previous templates also has one input variable it could also have several the input variable is called lessonsCounter , and it's defined via a ng-template property using the prefix let- The variable lessonsCounter is visible inside the ng-template body, but not outside the content of this variable is determined by the expression that its assigned to the property let-lessonsCounter That expression is evaluated against a context object, passed to ngTemplateOutlet together with the template to instantiate This context object must then have a property named estimate , for any value to be displayed inside the template the context object is passed to ngTemplateOutlet via the context property, that can receive any expression that evaluates to an object Given the example above, this is what would get rendered to the screen: Approximately 10 lessons This gives us a good overview of how to define and instantiate our own templates.
Template References The same way that we can refer to the loading template using a template reference, we can also have a template injected directly into our component using the ViewChild decorator: As we can see, the template can be injected just like any other DOM element or component, by providing the template reference name defaultTabButtons to the ViewChild decorator.
Configurable Components with Template Partial Inputs Let's take for example a tab container, where we would like to give the user of the component the possibility of configuring the look and feel of the tab buttons.
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