Upgrade project to Android M compatible

I know this can be a tricky question for some people, but I've been searching this article all day and trying to figure out how to set up a file build.gradle

in my Android project.

I am updating some APIs and preparing them for Android M. Now everything is fine. However, I'm confused in minSdkversion

, targetSdkversion

, complieSdkVersion

.

My current setup

android {
compileSdkVersion 'android-MNC'   //this was 21
buildToolsVersion "22.0.1"


defaultConfig {
    ...
    minSdkVersion 11
    targetSdkVersion 'MNC'   //this was 21
    ...
}
...

}

      

        
        
        
      

    

As you can see from the comments, my application was executed and targeted API21 before, and now I change it to MNC

to cover the whole range from api11

to MNC

.

These are my test cases,

Android M device (API22) --- OK

Android 5.1.1 device (API22) --- error and FAILED_OLDER_SDK

If I change my setting to

android {
compileSdkVersion 21
buildToolsVersion "22.0.1"


defaultConfig {
    ...
    minSdkVersion 11
    targetSdkVersion 21
    ...
}

      

        
        
        
      

    

Test cases,

Android M device (API22) --- OK

Android 5.1.1 device (API22) --- OK

Android 4.3.1 device (API18) --- OK // Why is this ok?

if a device with API18 can execute project against 21, then why Android 5.1.1 (API22) was unable to execute project against MNC?