Android studio: why are minSdkVersion and targetSdkVersion specified both in AndroidManifest.xml and build.gradle?

I just discovered something weird about Android studio: it has some configuration options in the build.gradle file that override what is specified in the AndroidManifest.xml file.

For instance, I had the following lines in build.gradle:

android {
    compileSdkVersion 18
    buildToolsVersion "18.1.1"

    defaultConfig {
        minSdkVersion 10
        targetSdkVersion 10
    }
...
}

which was overriding the corresponding tag in AndroidManifest.xml:

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="8"/>

I don't really like to have the same settings spread in two different files, so I am wondering if I can safely remove it either from build.gradle or AndroidManifest.xml and where it makes more sense to keep it.

Gradle overrides the manifest values, and I prefer to update the build.gradle file rather than the manifest. Probably this is the right way using Gradle. Gradle supports product flavours which can be controlled via an IDE and those product flavors can change many things in our Manifest like package name, version code, version name, target SDK and many other. Then by one click in Android Studio you can change many properties and generate another apk.

You can leave the manifest as it is and do all configuration in build.gradle. You can safely remove

<uses-sdk></uses-sdk>

from manifest as well as version codes.

From the Android docs:

> Note: If your app defines the app version directly in the element, the version values in the Gradle build file will override the settings in the manifest. Additionally, defining these settings in the Gradle build files allows you to specify different values for different versions of your app. For greater flexibility and to avoid potential overwriting when the manifest is merged, you should remove these attributes from the element and define your version settings in the Gradle build files instead.

https://developer.android.com/studio/publish/versioning.html#appversioning