After a successfull import of an Eclipse-Android-Project into "Android Studio 1.4" i get the error "Please select Android SDK" when I click on the button to run the application in simulator.
But I can't find any possibility to do that.
This dialog opens up when i click on "run":
This is the "project structure" dialog:
What to do now?
I go to build.gradle and click sync now. Then it worked.
Update :
Tools -> Android -> Sync Project with Gradle Files (Android Studio 3.0.1)
click this icon to sync gradle 
or edit any of your module gradle and then sync
Press "Ctrl+shift+A" and in the pop-up EditText, write "Sync Project with Gradle Files". After that double click on the appeared option. It will then sync your Gradle file SDK with the project file.
The comment from @Nisarg helped: "set latest version in Compile Sdk Version"
I changed from API 8 to API 23 and the error message disappeared.
Just change build tools version to 25.0.3.. and sync now I hope it will help..
This worked for me.
File -> Settings -> Android SDK -> Android SDK Location Edit -> Android SDK
app module. Then choose the Compile SDK version . Choose the latest one and click apply.
I just restarted my Android Studio, then it rebuilt the project, the error disappeared.
Follow these steps:
Hope this helps.
Just Go to the Gradle(app) file and Make Sync , once gradle shows Sync Complete then the Error. will gone
Cleaning and Re-syncing Gradle files worked for me.
After opening my project in Android Studio, I opened the App version of the build.gradle file, located in the Gradle Scripts folder of the Project. When I hovered my mouse pointer over the buildToolsVersion number, a tooltip popped, indicating that the version of Android Build Tools needed to be upgraded (see screenshot). I changed the value of the buildToolsVersion to the one identified by the error (27.0.2) and the problem was solved. The original error (Please select Android SDK) went away and the project compiled successfully, again. Although this solution was mentioned previously, the exact steps seemed to be missing, so hopefully this clears up any doubt. I guess the root cause for this problem is that a new version of the build tools were released but Android Studio did not trigger any notification to me, which would have indicated that I should manually fix this (since Android Studio does not seeem to have the ability to upgrade this build.gradle file internally), which leaves the onus on the user to find the problem and fix it.
In my case there there is no selected java sdk version in project structure-
I had to select the -
1.Source Compatibility (1.7)
2.Target Compatibility (1.7)
as shown in image.
open build.gradle file. just add a space or press enter. then sync project. it works...
I know it's an old question, but still might help somebody. In my case, I renamed the SDK directory, and restarted Studio, which forced it to ask for SDK location. After selecting SDK location, the error was gone.
Source Compatibility should be selected as the minimum Android Version that your app should be compatible with(usually selected as SDK 15), Target Compatibility should be selected as the newest Android Version that your app should be compatible with(SDK 23). Afterwards you want to check your AndroidMenifest and your gradle.build to see if its realy set to the properties selected if not you can just add it manually. and ofcourse you should check the SDK Location is actually pointing to your android studio SDK folder (if you are importing from Eclipse then you should point to your Eclipse SDK folder).
For Android Studio 2.1, click on Project, and you will see highlighted in red, a drop-down menu to select the missing information.
You are using Google API SDK. This for some reason doesn't work anymore with the embedded java JDK / JRE.
Follow the solution I described here and set Android Studio JDK path to your local JDK (ex. OpenJDK)
please check your sdk version and sdk tools are in the sdk manager and you project's gradle.properties setting such as : BUILD_TOOLS_VERSION=25.0.1 COMPILE_SDK_VERSION=25
Give SDK path in local.properties file as
sdk.dir=C\:\\Users\\System43\\AppData\\Local\\Android\\sdk and give latest version in compilesdk in gradle file.