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MDC 2022 Practical Blazor.pptx
- 7. PRACTICAL BLAZOR for Minnesota Developers Conference 2022 Patrick Szalapski Applications Architect, General Mills @Szalapski | szalapski.com
- 8. AGENDA 1. Cross-cutting concerns, such as profiling, using abstract components 2. Speeding up rendering with virtualization 3. Avoiding rerendering with abstract components 4. Breaking a Blazor component into subcomponents
- 9. DEMO • Ask me (now or afterward) about: • Mechanical keyboards • New File extension • Windows Terminal • Nullable and non-nullable references • Unhelpful VSPro removes “watch” • VS Intellisense slightly broken for Blazor • Refactor one step at a time, even if confident • Agile, Scrum, Kanban, team concerns This is Minnesota Developers Conference, not Minnesota Managers Conference: Let’s code, not read slides Tangents we might hit… dotnet watch vs. VS run speed up your development loop Blazor favicon animated glyph `null!` convention for required parameters
- 10. MAKING A SUBCOMPONENT IN BLAZOR 1.Insert (non-working) markup calling the new subcomponent above old markup 2.Copy the entire component as new component 3.Delete unnecessary markup and code in subcomponent 4.Add parameters 5.Add “…Changed” EventCallback parameters 6.Test and fix as doubled-up behavior 7.In the parent, delete the doubled-up markup, code, directives
- 11. MAKING A SUBCOMPONENT IN BLAZOR (ELABORATED) 1. Insert markup for the new subcomponent usage (above the markup that will be removed). 2. Copy the entire component to a new file. Rename it to match the above. 3. Edit the new subcomponent to delete all markup that should remain in the parent only. Delete all code that is thus unused. 4. Add parameters for missing references; supply them in the parent. 5. Add “…Changed” EventCallback parameters for anything editable. 6. Now you have a subcomponent that works and a parent that also works with its markup repeated (doubled up). Test and fix anything that is broken. 7. In the parent, delete the appropriate markup, code, and directives.
- 12. BINDING REFERENCE <select value="Bob" /> a literal string “Bob“, obviously <select value="@myName" /> one-way binding: the rendered option always gets the updated value of myName <select @value="myName" /> AVOID - error: '@value' is not a valid attribute name. <select @value="@myName" /> AVOID - error: '@value' is not a valid attribute name. <select value="@myName“ @onchange="handleChange" /> one-way binding with event on change, a good approach when custom logic is needed (e.g saving to a web API then conditionally updating the value); note, handleChange is a reference to a function that takes one parameger, a ChangeEventArgs instance. <select @bind="@myName" /> Two-way binding using the special value attribute and onchange event; same as <select value="@myName" onchange="e => myName = e.Value" /> <select @bind-Item="myName" /> (or any attribute, not just "value") Two-way binding; same as <select Item="@myName" ItemChanged="e => myName = e.Value" /> <select @bind-Item="myName" @bind-Item:event="oninput" /> Two-way binding using custom event; same as <select Item="@myName" @oninput="e => myName = e.Value" /> <MyComponent MyParameter1="@("firstName")" /> (Custom component) Literal string <MyComponent MyParameter1="firstName" /> NOT a literal string; passes the value of firstName as a one-way binding <MyComponent MyParameter1="@firstName" /> AVOID - redundant <MyComponent @MyParameter1="…" /> AVOID - ERROR - bad syntax <MyComponent @bind-MyParameter1="…" /> Two-way binding; same as <MyComponent MyParameter1="myName" MyParameter1Changed="e => myName = e.Value" /> (both the MyParameter1 parameter and the MyParameter1Changed event must
- 13. STRETCH GOAL: UNPREPARED BLAZOR CHAT • Get-only properties are better than mutating state • CallbackEvents can be bound to either synchronous or async methods • OnParametersSetAsync and OnAfterRender are the two methods you have to react to in a subcomponent
Notas do Editor
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- When I first started working in component-based frameworks like Vue.js and Blazor, my instinct was often to make loops and then call a method from a binding inside of the loop. After all, that's what we do in jQuery or even in everyday procedural programming, such as in a service or library function--when we have a loop, you use the properties of the objects we're looping over to make whatever call we want. But in web components, this logic can become much simpler by being eager to make a new subcomponent, moreso than your intuition might tell you. Usually breaking out the innards of a loop to its own component results in simpler code. Here's how you do it: In the original component, look at your loop; usually you will aim to refactor the entire contents of the loop (but not the loop flow control) into a new component. Choose a name for your component and insert markup for such an element (that doesn't yet exist), usually as the very first element inside the loop. It needs at least one parameter: the loop iteration reference. I like to name the parameter exactly the same as the loop iteration reference, as it makes the transition easier, which means it might be in camelCase and not PascalCase; this is temporary Copy the entire .razor component to a new .razor file that will become the child component. Rename the file to match the name you chose in step 1. If the component has a @page directive at the top of the new file, delete it. Rename that file to match the name you typed for the new element. Visual Studio unhelpfully edits your .csproj file to add a Watch-Remove element for the new component. I usually want to dotnet-watch all my components, so remove it from the .csproj file manually. Edit the new child component file markup to delete all content outside of and including the loop statement, leaving only the markup that was inside the loop. Add or modify the root-level element if desired. (I try always to have a root element with a class the same name as the component but in kebab-case.) Add a parameter member for the parameter you implied in step 1. It should be a public property with a getter and setter, and have a default value. Prefer it to be non-nullable if possible. Again, it might be in camelCase and not PascalCase; this is temporary. In the parent component, Visual Studio may give you the mistaken error "found markup with unexpected name", even though you are in the same folder and therefore the same namespace. Ignore it; it should compile anyway. This error might go away later when you reload Visual Studio. Look through the markup and see if there are any other missing references. There likely won't be, as you haven't yet deleted anything from the code section. If there are problems, fix them before continuing. At this point, your new markup in the parent component should work, and you should have a component that will compile and render the very same way, right above the old markup. Since you still have the same markup in the parent component, you can run it and see if you get the desired duplicated markup on the rendered page. If you do not, fix things before continuing. Put the new component and its parent on a diet Delete all the parts of the @code in the child component you no longer need; this is usually most of it. Also, delete any unneeded @inject directives and any unused @usings (for needs that were only in the parent and not here). Recompile and inspect it again, confirming that the new component is still identical to the old markup which still exists in the parent component. Go back to the parent component and delete the markup that is now being rendered in the child component. Also delete any code, @inject directives, or unused @usings that you can (for needs that were only in the child and not here). Recompile and inspect it again, confirming that the new component works well and that the old markup is gone. Fix its flaws Now that your component is fully baked, you can refactor it to make it simpler. Any bindings with arguments can likely now be argumentless, and the state for this iteration now simply becomes the state for the whole component instance. Finally, you can rename your new component's parameter to a better name with proper casing. Done!