From Unity to iOS, how to perfectly automate frameworks, settings and plist?

IMPORTANT:

Very unfortunately you can not use System.xml here as you would expect, since, Apple's plist format is insane. You probably have to use a munge.

For 2019 ...

Filename, BuildPostProcessor.cs

Put it in the folder Assets/Editor/ . (Just make the folder "Editor/" exactly there if it does not exist.)

This shows how to do all three of frameworks, settings and plist.

// filename BuildPostProcessor.cs
// put it in a folder Assets/Editor/
using System.IO;
using UnityEngine;
using UnityEditor;
using UnityEditor.Callbacks;
using UnityEditor.iOS.Xcode;

public class BuildPostProcessor {

    [PostProcessBuild]
    public static void ChangeXcodePlist(BuildTarget buildTarget, string path) {

        if (buildTarget == BuildTarget.iOS) {

            string plistPath = path + "/Info.plist";
            PlistDocument plist = new PlistDocument();
            plist.ReadFromFile(plistPath);

            PlistElementDict rootDict = plist.root;

            Debug.Log(">> Automation, plist ... <<");

            // example of changing a value:
            // rootDict.SetString("CFBundleVersion", "6.6.6");

            // example of adding a boolean key...
            // < key > ITSAppUsesNonExemptEncryption </ key > < false />
            rootDict.SetBoolean("ITSAppUsesNonExemptEncryption", false);

            File.WriteAllText(plistPath, plist.WriteToString());
        }
    }

    [PostProcessBuildAttribute(1)]
    public static void OnPostProcessBuild(BuildTarget target, string path) {

        if (target == BuildTarget.iOS) {

            PBXProject project = new PBXProject();
            string sPath = PBXProject.GetPBXProjectPath(path);
            project.ReadFromFile(sPath);

            string tn = PBXProject.GetUnityTargetName();
            string g = project.TargetGuidByName(tn);

            ModifyFrameworksSettings(project, g);

            // modify frameworks and settings as desired
            File.WriteAllText(sPath, project.WriteToString());
        }
    }

    static void ModifyFrameworksSettings(PBXProject project, string g) {

        // add hella frameworks

        Debug.Log(">> Automation, Frameworks... <<");

        project.AddFrameworkToProject(g, "blah.framework", false);
        project.AddFrameworkToProject(g, "libz.tbd", false);

        // go insane with build settings

        Debug.Log(">> Automation, Settings... <<");

        project.AddBuildProperty(g,
            "LIBRARY_SEARCH_PATHS",
            "../blahblah/lib");

        project.AddBuildProperty(g,
            "OTHER_LDFLAGS",
            "-lsblah -lbz2");

        // note that, due to some Apple shoddyness, you usually need to turn this off
        // to allow the project to ARCHIVE correctly (ie, when sending to testflight):
        project.AddBuildProperty(g,
            "ENABLE_BITCODE",
            "false");
    }

}

That will do it.

Note - the final part of the puzzle is copying across files (perhaps data files or text files). In reality it's best to just use the "StreamingAssets/" approach, explained fully in this QA.

Fixed code for Unity 2019.3:

// filename BuildPostProcessor.cs
// put it in a folder Assets/Editor/
using System.IO;
using UnityEngine;
using UnityEditor;
using UnityEditor.Callbacks;
using UnityEditor.iOS.Xcode;

public class BuildPostProcessor
{

    [PostProcessBuild]
    public static void ChangeXcodePlist(BuildTarget buildTarget, string path)
    {

        if (buildTarget == BuildTarget.iOS)
        {

            string plistPath = path + "/Info.plist";
            PlistDocument plist = new PlistDocument();
            plist.ReadFromFile(plistPath);

            PlistElementDict rootDict = plist.root;

            Debug.Log(">> Automation, plist ... <<");

            // example of changing a value:
            // rootDict.SetString("CFBundleVersion", "6.6.6");

            // example of adding a boolean key...
            // < key > ITSAppUsesNonExemptEncryption </ key > < false />
            rootDict.SetBoolean("ITSAppUsesNonExemptEncryption", false);

            File.WriteAllText(plistPath, plist.WriteToString());
        }
    }

    [PostProcessBuildAttribute(1)]
    public static void OnPostProcessBuild(BuildTarget target, string path)
    {

        if (target == BuildTarget.iOS)
        {

            PBXProject project = new PBXProject();
            string sPath = PBXProject.GetPBXProjectPath(path);
            project.ReadFromFile(sPath);

            string g = project.GetUnityFrameworkTargetGuid();

            ModifyFrameworksSettings(project, g);

            // modify frameworks and settings as desired
            File.WriteAllText(sPath, project.WriteToString());
        }
    }

    static void ModifyFrameworksSettings(PBXProject project, string g)
    {

        // add hella frameworks

        Debug.Log(">> Automation, Frameworks... <<");

        project.AddFrameworkToProject(g, "blah.framework", false);
        project.AddFrameworkToProject(g, "libz.tbd", false);

        // go insane with build settings

        Debug.Log(">> Automation, Settings... <<");

        project.AddBuildProperty(g,
            "LIBRARY_SEARCH_PATHS",
            "../blahblah/lib");

        project.AddBuildProperty(g,
            "OTHER_LDFLAGS",
            "-lsblah -lbz2");

        // note that, due to some Apple shoddyness, you usually need to turn this off
        // to allow the project to ARCHIVE correctly (ie, when sending to testflight):
        project.AddBuildProperty(g,
            "ENABLE_BITCODE",
            "false");
    }

}