使用Android Studio，我之前安装了APK的未签名调试版本(Build > Build APK)，在安装有签名的发布版本之前必须卸载它(Build Variant > Build Variant: release, Build > Generate signed APK)。

Clearly there are many causes of this problem. For me the situation was this: I had deployed to my nexus 7 (actual device) from within the Android Studio (v1.3.2). All worked fine. I then created a signed apk and uploaded to my Google Drive. After disconnecting my nexus from the usb, I went to the settings/apps and uninstalled my app (App1). I then opened google drive and clicked on my App1.apk and chose to install it (need to ensure you have allowed installation of apks in settings). Then I got the dreaded message "App not Installed"

Solution for me: go back into settings/apps and scroll though all apps and at the bottom was a pale version of my App1 (note the original App1 was at the top in Alphabetical order which was deleted as above). When clicking on the pale version it said "Not installed for this user". (I had set up my nexus to have more than one user). But in the top right corner there is a three dot button. I pressed this and it said "Uninstall for all users". Which I did and it fixed the problem. I was now able to click on App1.apk and it installed fine without the error.

我曾以各种形式遇到过这个问题，但这一次是一个新的问题:

在这种情况下，我有提供商名称冲突-相同的提供商名称存在于我的应用程序和我的另一个应用程序。

我遇到了类似的问题，这是因为我试图在使用相同apk的先前版本的手机上安装apk，而两个apk没有使用相同的证书进行签名。我的意思是，当我使用相同的证书时，我能够覆盖以前的安装，但当我在不同版本之间更改证书时，安装就不可能了。您是否使用相同的证书?

如果你在AndroidManifest.xml中声明了两次MainActivity，就会发生这种情况。

另一个可能的原因是:您更改了启动活动。提示:永远不要对已经发布的应用程序这样做!原因在Android开发者博客中讨论过。

如果您有该应用程序的以前版本，请先尝试删除它，现在我的问题已通过该方法解决。