APK がインストールできない：エラー文別に全原因を解説

adb install Builds/game.apk
# Failure [INSTALL_FAILED_UPDATE_INCOMPATIBLE: Package com.yourstudio.yourgame
#   signatures do not match previously installed version; ignoring!]   -> a different key
# Failure [INSTALL_FAILED_VERSION_DOWNGRADE: Downgrade detected]        -> older versionCode
# Failure [INSTALL_FAILED_OLDER_SDK: ... is greater than the device ...] -> API too low
# Failure [INSTALL_FAILED_NO_MATCHING_ABIS: Failed to extract native libraries] -> wrong ABI

# what the phone actually is, and whether an old copy survived
adb shell getprop ro.build.version.sdk
adb shell getprop ro.product.cpu.abi
adb shell pm list packages | grep yourgame

adb uninstall com.yourstudio.yourgame
adb install Builds/game.apk

# clear last run, then watch only Unity's lines while you reproduce it
adb logcat -c
adb logcat -s Unity

# nothing under the Unity tag? then it is a native crash, not a C# one
adb logcat -d > full-log.txt
grep -iE "fatal|androidruntime|libc |SIGSEGV" full-log.txt

# what Android thinks you actually installed, in one shot
adb shell dumpsys package com.yourstudio.yourgame | grep -E "versionCode|minSdk|targetSdk"

using UnityEngine;
using UnityEngine.Networking;

public class LoadOnDevice : MonoBehaviour
{
    // File.ReadAllText works in the editor and returns nothing on Android:
    // StreamingAssets sits inside the APK there, not on the filesystem.
    IEnumerator Start()
    {
        string path = Application.streamingAssetsPath + "/levels.json";

        using var request = UnityWebRequest.Get(path);
        yield return request.SendWebRequest();

        if (request.result != UnityWebRequest.Result.Success)
        {
            Debug.LogError($"Cannot read {path}: {request.error}");
            yield break;
        }

        var data = JsonUtility.FromJson<LevelList>(request.downloadHandler.text);
        Debug.Log($"Loaded {data.levels.Length} levels");
    }
}

<!-- Anywhere under Assets/ — Unity picks up every link.xml it finds. -->
<linker>
  <assembly fullname="Assembly-CSharp">
    <!-- keep what only reflection can reach: JSON classes, Activator targets -->
    <namespace fullname="Game.Data" preserve="all" />
    <type fullname="Game.Skills.Fireball" preserve="all" />
  </assembly>
  <assembly fullname="Newtonsoft.Json" preserve="all" />
</linker>