For my Canadian Classifieds Alerter app, I needed to implement a hierarchy like structure to represent locations and categories. This is what I used in my solution.
For example,
Buy N’ Sell -> Computers -> Laptops
Canada -> New Brunswick -> Moncton
Laptops belongs to Computers, which a sub category of Buy N’ Sell’
Moncton belongs to New Brunswick, which belongs to Canada
Solution
Here it is in it’s simplest form. We’ll actually make it do something further down.
public enum KijijiCategory { //root category CATEGORY(null), //buy n sell, pass in the root category as the parent BUY_N_SELL(CATEGORY), //Pass in Buy N Sell as the parent category COMPUTERS(BUY_N_SELL), //Pass in Computers as the parent category LAPTOPS(COMPUTERS), private KijijiCategory parent = null; //Constructor, you pass in the parent KijijiCategory(KijijiCategory parent) { this.parent = parent; } }
General explanation of what’s going on:
For CATEGORY, there is no parent, so I pass in null.
For BUY_N_SELL, the parent is CATEGORY, so I pass it in
For COMPUTERS, the parent is BUY_N_SELL, so I pass it in.
For LAPTOPS, the parent is COMPUTERS, so I pass it in.
Are you starting to see where this is going?
What can we use it for?
Check out this video.
Notice how easy it is to traverse through menu options? To do this we’re going to have to add more to the code I posted above
public enum KijijiCategory { //root category CATEGORY(null), //buy n sell, pass in the root category as the parent BUY_N_SELL(CATEGORY, 10, "Buy n sell"), //Pass in Buy N Sell as the parent category COMPUTERS(BUY_N_SELL, 16, "Computers"), //Pass in Computers as the parent category LAPTOPS(COMPUTERS,773, "Laptops"), private KijijiCategory parent = null; //unique identifier used internally by my app, you might not //need this or you may need to add your own private int id; //title will give us a nicer looking private String title = ""; //In this example KijijiCategory(KijijiCategory parent) { this.parent = parent; } //This is the constructor used by almost all of the categories above KijijiCategory(KijijiCategory parent, int id, String title) { this.parent = parent; this.id = id; this.title = title; } /* * Getters * */ public String getTitle() { return this.title; } public String getParentName() { if (parent == null) { return "none"; } else { return parent.getTitle(); } } public KijijiCategory getParentCategory() { return parent; } public int getId() { return this.id; } @Override public String toString() { return "Kijiji Category name of: " + this.getTitle() + " and id of " + this.getId() + " and a parent of " + getParentName(); } }
You’ll notice I added a new constructor. I’m passing in an internally used identifier, and a nicer to look at string called title we’ll use to set the text for the boxes. I also added a few getters and overrode the toString() method
This is how I generated the LinearLayout
First step is to call the new method in onCreate (I prefer to keep this stuff out of onCreate as it makes future modifications easier)
generateKijijiCategories(KijijiCategory.CATEGORY, categoryLayout);
Here is where all the buttons are generated.
private LinearLayout generateKijijiCategories(final KijijiCategory categoryParent, final LinearLayout categoryLayout) { //Shows all of the buttons if we're on the main category if (categoryParent == KijijiCategory.CATEGORY) { final Button button = new Button(this); button.setText("All Categories"); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { button.setTextColor(Color.GREEN); categoryToQuery = KijijiCategory.CATEGORY; } }); categoryLayout.addView(button); } //iterate through all potential values for (final KijijiCategory kijijiCategory : KijijiCategory.values()) { //abandon the current iteration if it's not a child of the parent we passed in if (kijijiCategory.getParentCategory() != categoryParent) { continue; } //Instantiate a button final Button button = new Button(this); //Give it a nice looking text button.setText(kijijiCategory.getTitle()); //Used internally in my app button.setId(kijijiCategory.getId()); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //turns focus to the top txtCategories.requestFocus(); //empty out all buttons categoryLayout.removeAllViews(); button.setTextColor(Color.GREEN); categoryLayout.addView(button); categoryToQuery = kijijiCategory; //This isn't true recursion, it's debateable though generateKijijiCategories(kijijiCategory, categoryLayout); } }); //add the button to the layout categoryLayout.addView(button); } //add back button! if (categoryParent != KijijiCategory.CATEGORY) { Button backButton = new Button(this); final Button parentButton = new Button(this); parentButton.setText(categoryParent.getParentCategory().getTitle()); parentButton.setTextColor(Color.GREEN); backButton.setText("Back"); backButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { txtCategories.requestFocus(); categoryLayout.removeAllViews(); if(categoryParent.getParentCategory() != KijijiCategory.CATEGORY) { categoryLayout.addView(parentButton); } categoryToQuery = categoryParent.getParentCategory(); generateKijijiCategories(categoryToQuery, categoryLayout); } }); categoryLayout.addView(backButton); } return categoryLayout; }
See not so bad!