Android8.0后需要使应用可以安装未知来源应用才可以安装更新包，做内部更新
设置res->xml->file_path.xml

<?xml version="1.0" encoding="utf-8"?>
<paths>
    <external-path path="Android/data/此处填写applicationId（即包名）/"        name="files_root" />
    <external-path path="." name="external_storage_root" />
</paths>

AndroidManifest文件配置

<application>
    <provider
            android:name="android.support.v4.content.FileProvider"
            android:authorities="此处填写applicationId（即包名）.fileprovider"
            android:exported="false"
            android:grantUriPermissions="true">

            <!-- 元数据 -->
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/file_paths" />
    </provider>
</application>

新建工具类

public class InstallAppUtils {

    public static void installApp(Context context , File updateFile) {
        // 核心是下面几句代码
        if (null != updateFile) {
            try {
                Intent intent = new Intent(Intent.ACTION_VIEW);
                //兼容7.0
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
                    intent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
                    Uri contentUri = FileProvider.getUriForFile(context, "此处填写applicationId（即包名).fileprovider", updateFile);
                    intent.setDataAndType(contentUri, "application/vnd.android.package-archive");
                    //兼容8.0
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                        boolean hasInstallPermission = mActivity.getPackageManager().canRequestPackageInstalls();
                        if (!hasInstallPermission) {
                            ToastUtil.showLong("请在设置界面设置本应用允许安装应用");
                            startInstallPermissionSettingActivity(context);
                            return;
                        }
                    }
                } else {
                    intent.setDataAndType(Uri.fromFile(updateFile), "application/vnd.android.package-archive");
                    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                }
                if (mActivity.getPackageManager().queryIntentActivities(intent, 0).size() > 0) {
                    mActivity.startActivity(intent);
                }
            } catch (Throwable e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 跳转到设置-允许安装未知来源-页面
     */
    @RequiresApi(api = Build.VERSION_CODES.O)
    private static void startInstallPermissionSettingActivity(Context context) {
        //注意这个是8.0新API
        Intent intent = new Intent(Settings.ACTION_MANAGE_UNKNOWN_APP_SOURCES);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        mActivity.startActivity(intent);
    }
}

调用

    InstallAppUtils.installApp(context, updateApk)