MVVM

Transcript

1. MVVM Model – View – ViewModel
2. WHAT IS MVVM?
3. IT'S LIKE MVC, BUT DIFFERENT.
4. BUT IT'S NOT THAT DIFFERENT.
5. IT'S JUST DIFFERENT ENOUGH.
6. Example: IPHONE RECIPE APP A TABLE OF RECIPES GROUPED ALPHABETICALLY
7. MVC 1.0
8. - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return self.fetchedResultsController.sections.count; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { id<NSFetchedResultsSectionInfo> info = self.fetchedResultsController.sections[section]; return info.numberOfObjects; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:...]; RCPRecipe *recipe = [self.fetchedResultsController objectAtIndexPath:indexPath]; cell.textLabel.text = [NSString stringWithFormat:@"%@ by %@", recipe.name, recipe.author.name]; return cell; }
9. MVC 1.0 ▸ Logic is tied to presentation ▸ It can only be tested visually ▸ The code is verbose ▸ Tightly coupled to the database and model ▸ No separation of concerns
10. MVC 2.0
11. - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return self.numberOfSections; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [self numberOfRecipesInSection:section]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:...]; RCPRecipe *recipe = [self recipeAtIndexPath:indexPath]; cell.textLabel.text = [NSString stringWithFormat:@"%@ by %@", recipe.name, recipe.author.name]; return cell; }
12. - (NSInteger)numberOfSections { return self.fetchedResultsController.sections.count; } - (NSInteger)numberOfRecipesInSection:(NSInteger)section { id<NSFetchedResultsSectionInfo> info = self.fetchedResultsController.sections[section]; return info.numberOfObjects; } - (RCPRecipe *)recipeAtIndexPath:(NSIndexPath *)indexPath { return [self.fetchedResultsController objectAtIndexPath:indexPath]; }
13. MVC 2.0 ▸ Some logic could be tested in code ▸ Partial separation of concerns ▸ Reusable methods for getting model objects ▸ Slightly less verbose
14. MVC 2.0 ▸ Some logic is still tied to presentation ▸ Still requires visual testing ▸ Tightly coupled to the model
15. MVC 3.0
16. - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return self.numberOfSections; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [self numberOfRecipesInSection:section]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:...]; RCPRecipe *recipe = [self recipeAtIndexPath:indexPath]; cell.textLabel.text = [self displayNameForRecipe:recipe]; return cell; }
17. MVC 3.0 ▸ Logic is testable in code ▸ Separation of concerns
18. MVC 3.0 ▸ Tightly coupled to the model ▸ Testing per-row logic requires an entire table view ▸ Logic could easily depend on view
19. MVVM
20. - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return self.viewModel.numberOfSections; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [self.viewModel numberOfRecipesInSection:section]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:...]; RCPRecipeViewModel *viewModel = [self.viewModel viewModelAtIndexPath:indexPath]; cell.textLabel.text = viewModel.displayName; return cell; }
21. @interface RCPRecipeListViewModel : NSObject @property (assign, nonatomic) NSInteger numberOfSections; - (NSInteger)numberOfRecipesInSection:(NSInteger)section; - (RCPRecipeViewModel *)viewModelAtIndexPath:(NSIndexPath *)indexPath; @end
22. @interface RCPRecipeViewModel : NSObject @property (copy, nonatomic) NSString *displayName; - (instancetype)initWithRecipe:(RCPRecipe *)recipe; @end
23. MVVM ▸ Separation of concerns ▸ Testable in code ▸ Easy to test per-row logic ▸ Loosely coupled ▸ Independent of UIKit/AppKit ▸ Easily have different row types
24. Q & A