Android Exception - Package cn.itmob.demo new target SDK 21 doesn't support runtime permissions

1. 异常

安装应用时遇到如下情况的错误信息：

1. 使用 PackageInstaller 安装应用时 Logcat 输出如下错误：

Package cn.itmob.demo new target SDK 21 doesn't support runtime permissions but the old target SDK 27 does.

1. 使用 adb 安装应用时输入如下错误：

> adb install TestApp.apk
Performing Streamed Install
adb: failed to install TestApp.apk: Failure [-26: Package cn.itmob.demo new target SDK 21 doesn't support runtime permissions but the old target SDK 27 does.]

或者：

Installation error: INSTALL_FAILED_PERMISSION_MODEL_DOWNGRADE
Please check logcat output for more details.
Launch canceled!

2. 解决：

因为从 Android 6.0（API 级别 23） 版本开始，升级应用时新增了限制条件，如果已安装版本支持运行时权限（targetSDKVersion > 22）那么升级时的新版本的 targetSDKVerssion 也必须大于 22。

因为从 Android 6.0（API 级别 23）开始敏感权限不再是在安装时授予，但必须由应用程序在运行时通过 requestPermissions 请求。

如下是 Android 源码中关于改限制的代码：

InstallPackageHelper.java

if (replace) {
    // Prevent apps opting out from runtime permissions
    AndroidPackage oldPackage = mPm.mPackages.get(pkgName);
    final int oldTargetSdk = oldPackage.getTargetSdkVersion();
    final int newTargetSdk = parsedPackage.getTargetSdkVersion();
    if (oldTargetSdk > Build.VERSION_CODES.LOLLIPOP_MR1
            && newTargetSdk <= Build.VERSION_CODES.LOLLIPOP_MR1) {
        throw new PrepareFailure(
                PackageManager.INSTALL_FAILED_PERMISSION_MODEL_DOWNGRADE,
                "Package " + parsedPackage.getPackageName()
                        + " new target SDK " + newTargetSdk
                        + " doesn't support runtime permissions but the old"
                        + " target SDK " + oldTargetSdk + " does.");
    }
    ...
}

上面的错误信息就是因为已安装了 targetSDKVerssion 是 27 的应用，重新安装的应用 targetSDKVerssion 是 21。

解决办法：

1. 修改新版本的 targetSDKVerssion，保证其不低于之前的版本
2. 卸载旧版本重新安装

这个限制无法通过 adb install -r 或 adb install -d 来安装

> adb install -r -d TestApp.apk
Performing Streamed Install
adb: failed to install TestApp.apk: Failure [-26: Package cn.itmob.demo new target SDK 21 doesn't support runtime permissions but the old target SDK 27 does.]