--- layout: documentation title: Build Tutorial - iOS --- Introduction to Bazel: Building an iOS App ========== In this tutorial, you will learn how to build a simple iOS app. You'll do the following: * [Set up your environment](#set-up-your-environment) * [Install Bazel](#install-bazel) * [Install Xcode](#install-xcode) * [Get the sample project](#get-the-sample-project) * [Set up a workspace](#set-up-a-workspace) * [Create a WORKSPACE file](#create-a-workspace-file) * [Update the WORKSPACE file](#update-the-workspace-file) * [Review the source files](#review-the-source-files) * [Create a BUILD file](#create-a-build-file) * [Add the rule load statement](#add-the-rule-load-statement) * [Add an objc_library rule](#add-an-objc_library-rule) * [Add an ios_application rule](#add_an-ios_application-rule) * [Build and deploy the app](#build-and-deploy-the-app) * [Build the app for the simulator](#build-the-app-for-the-simulator) * [Find the build outputs](#find-the-build-outputs) * [Run and debug the app in the simulator](#run-and-debug-the-app-in-the-simulator) * [Build the app for a device](#build-the-app-for-a-device) * [Install the app on a device](#install-the-app-on-a-device) * [Review your work](#review-your-work) ## Set up your environment To get started, install Bazel and Xcode, and get the sample project. ### Install Bazel Follow the [installation instructions](../install.md) to install Bazel and its dependencies. ### Install Xcode Download and install [Xcode](https://developer.apple.com/xcode/downloads/). Xcode contains the compilers, SDKs, and other tools required by Bazel to build Apple applications. ### Get the sample project You also need to get the sample project for the tutorial from GitHub. The GitHub repo has two branches: `source-only` and `master`. The `source-only` branch contains the source files for the project only. You'll use the files in this branch in this tutorial. The `master` branch contains both the source files and completed Bazel `WORKSPACE` and `BUILD` files. You can use the files in this branch to check your work when you've completed the tutorial steps. Enter the following at the command line to get the files in the `source-only` branch: ```bash cd $HOME git clone -b source-only https://github.com/bazelbuild/examples ``` The `git clone` command creates a directory named `$HOME/examples/`. This directory contains several sample projects for Bazel. The project files for this tutorial are in `$HOME/examples/tutorial/ios-app`. ## Set up a workspace A [workspace](../build-ref.html#workspaces) is a directory that contains the source files for one or more software projects, as well as a `WORKSPACE` file and `BUILD` files that contain the instructions that Bazel uses to build the software. The workspace may also contain symbolic links to output directories. A workspace directory can be located anywhere on your filesystem and is denoted by the presence of the `WORKSPACE` file at its root. In this tutorial, your workspace directory is `$HOME/examples/tutorial/`, which contains the sample project files you cloned from the GitHub repo in the previous step. Note that Bazel itself doesn't impose any requirements for organizing source files in your workspace. The sample source files in this tutorial are organized according to conventions for the target platform. For your convenience, set the `$WORKSPACE` environment variable now to refer to your workspace directory. At the command line, enter: ```bash export WORKSPACE=$HOME/examples/tutorial ``` ### Create a WORKSPACE file Every workspace must have a text file named `WORKSPACE` located in the top-level workspace directory. This file may be empty or it may contain references to [external dependencies](../external.html) required to build the software. For now, you'll create an empty `WORKSPACE` file, which simply serves to identify the workspace directory. In later steps, you'll update the file to add external dependency information. Enter the following at the command line: ```bash touch $WORKSPACE/WORKSPACE open -a Xcode $WORKSPACE/WORKSPACE ``` This creates and opens the empty `WORKSPACE` file. ### Update the WORKSPACE file To build applications for Apple devices, Bazel needs to pull the latest [Apple build rules](https://github.com/bazelbuild/rules_apple) from its GitHub repository. To enable this, add the following [`git_repository`](../be/workspace.html#git_repository) rules to your `WORKSPACE` file: ``` git_repository( name = "build_bazel_rules_apple", remote = "https://github.com/bazelbuild/rules_apple.git", tag = "0.4.0", ) git_repository( name = "bazel_skylib", remote = "https://github.com/bazelbuild/bazel-skylib.git", tag = "0.3.1", ) ``` **NOTE:** "Always use the [latest version of the build_apple rules](https://github.com/bazelbuild/rules_apple/releases) in the `tag` attribute. Make sure to check the latest dependencies required in `rules_apple`'s [project](https://github.com/bazelbuild/rules_apple)." **NOTE:** You **must** set the value of the `name` attribute in the `git_repository` rule to `build_bazel_rules_apple` or the build will fail. ## Review the source files Take a look at the source files for the app located in `$WORKSPACE/ios-app/UrlGet`. Again, you're just looking at these files now to become familiar with the structure of the app. You don't have to edit any of the source files to complete this tutorial. ## Create a BUILD file At a command-line prompt, open a new `BUILD` file for editing: ```bash touch $WORKSPACE/ios-app/BUILD open -a Xcode $WORKSPACE/ios-app/BUILD ``` ### Add the rule load statement To build iOS targets, Bazel needs to load build rules from its GitHub repository whenever the build runs. To make these rules available to your project, add the following load statement to the beginning of your `BUILD` file: ``` load("@build_bazel_rules_apple//apple:ios.bzl", "ios_application") ``` We only need to load the `ios_application` rule because the `objc_library` rule is built into the Bazel package. ### Add an objc_library rule Bazel provides several build rules that you can use to build an app for the iOS platform. For this tutorial, you'll first use the [`objc_library`](../be/objective-c.html#objc_library) rule to tell Bazel how to build a static library from the app source code and Xib files. Then you'll use the [`ios_application`](https://github.com/bazelbuild/rules_apple) rule to tell it how to build the application binary and the `.ipa` bundle. **NOTE:** This tutorial presents a minimal use case of the Objective-C rules in Bazel. For example, you have to use the `ios_application` rule to build multi-architecture iOS apps. Add the following to your `BUILD` file: ```python objc_library( name = "UrlGetClasses", srcs = [ "UrlGet/AppDelegate.m", "UrlGet/UrlGetViewController.m", "UrlGet/main.m", ], hdrs = glob(["UrlGet/*.h"]), xibs = ["UrlGet/UrlGetViewController.xib"], ) ``` Note the name of the rule, `UrlGetClasses`. ### Add an ios_application rule The [`ios_application`](../be/objective-c.html#ios_application) rule builds the application binary and creates the `.ipa` bundle file. Add the following to your `BUILD` file: ```python ios_application( name = "ios-app", bundle_id = "Google.UrlGet", families = [ "iphone", "ipad", ], minimum_os_version = "9.0", infoplists = [":UrlGet/UrlGet-Info.plist"], visibility = ["//visibility:public"], deps = [":UrlGetClasses"], ) ``` **NOTE:** Please update the `minimum_os_version` attribute to the minimum version of iOS that you plan to support. Note how the `deps` attribute references the output of the `UrlGetClasses` rule you added to the `BUILD` file above. Now, save and close the file. You can compare your `BUILD` file to the [completed example](https://github.com/bazelbuild/examples/blob/master/tutorial/ios-app/BUILD) in the `master` branch of the GitHub repo. ## Build and deploy the app You are now ready to build your app and deploy it to a simulator and onto an iOS device. **NOTE:** The app launches standalone but requires a backend server in order to produce output. See the README file in the sample project directory to find out how to build the backend server. ### Build the app for the simulator Make sure that your current working directory is inside your Bazel workspace: ```bash cd $WORKSPACE ``` Now, enter the following to build the sample app: ```bash bazel build //ios-app:ios-app ``` Bazel launches and builds the sample app. During the build process, its output will appear similar to the following: ```bash INFO: Found 1 target... Target //ios-app:ios-app up-to-date: bazel-bin/ios-app/ios-app.ipa INFO: Elapsed time: 0.565s, Critical Path: 0.44s ``` ### Find the build outputs The `.ipa` file and other outputs are located in the `$WORKSPACE/bazel-bin/ios-app` directory. ### Run and debug the app in the simulator You can now run the app from Xcode using the iOS Simulator. First, [generate an Xcode project using Tulsi](http://tulsi.bazel.io/). Then, open the project in Xcode, choose an iOS Simulator as the runtime scheme, and click **Run**. **Note:** If you modify any project files in Xcode (for example, if you add or remove a file, or add or change a dependency), you must rebuild the app using Bazel, re-generate the Xcode project in Tulsi, and then re-open the project in Xcode. ### Build the app for a device To build your app so that it installs and launches on an iOS device, Bazel needs the appropriate provisioning profile for that device model. Do the following: 1. Go to your [Apple Developer Account](https://developer.apple.com/account) and download the appropriate provisioning profile for your device. See [Apple's documentation](https://developer.apple.com/library/ios/documentation/IDEs/Conceptual/AppDistributionGuide/MaintainingProfiles/MaintainingProfiles.html) for more information. 2. Move your profile into `$WORKSPACE`. 3. (Optional) Add your profile to your `.gitignore` file. 4. Add the following line to the `ios_application` target in your `BUILD` file: ```python provisioning_profile = ".mobileprovision", ``` **NOTE:** Ensure the profile is correct so that the app can be installed on a device. Now build the app for your device: ```bash bazel build //ios-app:ios-app --ios_multi_cpus=armv7,arm64 ``` This builds the app as a fat binary. To build for a specific device architecture, designate it in the build options. To build for a specific Xcode version, use the `--xcode_version` option. To build for a specific SDK version, use the `--ios_sdk_version` option. The `--xcode_version` option is sufficient in most scenarios. To specify a minimum required iOS version, add the `minimum_os_version` parameter to the `ios_application` build rule in your `BUILD` file. You can also use [Tulsi](http://tulsi.bazel.io/docs/gettingstarted.html) to build your app using a GUI rather than the command line. ### Install the app on a device The easiest way to install the app on the device is to launch Xcode and use the `Windows > Devices` command. Select your plugged-in device from the list on the left, then add the app by clicking the **Add** (plus sign) button under "Installed Apps" and selecting the `.ipa` file that you built. If your app fails to install on your device, ensure that you are specifying the correct provisioning profile in your `BUILD` file (step 4 in the previous section). If your app fails to launch, make sure that your device is part of your provisioning profile. The `View Device Logs` button on the `Devices` screen in Xcode may provide other information as to what has gone wrong. ## Review your work In this tutorial, you used Bazel to build an iOS app. To accomplish that, you: * Set up your environment by installing Bazel and Xcode, and downloading the sample project * Set up a Bazel [workspace](workspace.md) that contained the source code for the app and a `WORKSPACE` file that identifies the top level of the workspace directory * Updated the `WORKSPACE` file to contain references to the required external dependencies * Created a `BUILD` file * Ran Bazel to build the app for the simulator and an iOS device * Ran the app in the simulator and on an iOS device The built app is located in the `$WORKSPACE/bazel-bin` directory. Completed `WORKSPACE` and `BUILD` files for this tutorial are located in the [master branch](https://github.com/bazelbuild/examples/tree/master/tutorial) of the GitHub repo. You can compare your work to the completed files for additional help or troubleshooting.