Hack to modify xxxSdVersion for building pre-N apk against preview SDK

Modify the minSdkVersion and targetSdkVersion in generated manifest

Change-Id: I8470693c0a316a3ad12a196bdd8f1c257da9e6c8

Author: tony-mak

app/build.gradle

@@ -50,14 +50,35 @@ android {
 
     productFlavors {
         standard {
+            minSdkVersion 21
             targetSdkVersion 23
         }
 
         N {
+            minSdkVersion 'N'
             targetSdkVersion 'N'
         }
     }
 
+    /* TODO: remove once release version of N sdk is released */
+       applicationVariants.all { variant ->
+           variant.outputs.each { output ->
+               output.processManifest.doLast {
+                   // minSdkVersion and targetSdkVersion are overridden if we build against preview
+                   // SDK, let us override them again here.
+                   minSdkVersion = variant.getMergedFlavor().minSdkVersion.getApiString();
+                   targetSdkVersion = variant.getMergedFlavor().targetSdkVersion.getApiString();
+
+                   def manifestOutFile = output.processManifest.manifestOutputFile
+                   def newFileContents = manifestOutFile.getText('UTF-8').
+                           replace('android:minSdkVersion="N"',
+                                   'android:minSdkVersion="' + minSdkVersion + '"')
+                   newFileContents = newFileContents.replace('android:targetSdkVersion="N"',
+                           'android:targetSdkVersion="' + targetSdkVersion + '"')
+                   manifestOutFile.write(newFileContents, 'UTF-8')
+               }
+           }
+       }
 }
 
 dependencies {