Prohibit uninstall of the default (or only) home app

We suppress the ability to uninstall (including uninstall of updates to
system-bundled apps) when the package in question is either the only
installed home app, or has been explicitly tagged by the user as the
"every time" home app among all those installed.

Bug 14162565

Change-Id: I582bb0d2abf0911ac68813f4c7e6fd7d17bfc2ca

src/com/android/settings/applications/InstalledAppDetails.java

@@ -366,11 +366,28 @@ public class InstalledAppDetails extends Fragment
                 mUninstallButton.setText(R.string.uninstall_text);
             }
         }
-        // If this is a device admin, it can't be uninstall or disabled.
+        // If this is a device admin, it can't be uninstalled or disabled.
         // We do this here so the text of the button is still set correctly.
         if (mDpm.packageHasActiveAdmins(mPackageInfo.packageName)) {
             enabled = false;
         }
+
+        // If this is the default (or only) home app, suppress uninstall (even if
+        // we still think it should be allowed for other reasons)
+        if (enabled && mHomePackages.contains(mPackageInfo.packageName)) {
+            ArrayList<ResolveInfo> homeActivities = new ArrayList<ResolveInfo>();
+            ComponentName currentDefaultHome  = mPm.getHomeActivities(homeActivities);
+            if (currentDefaultHome == null) {
+                // No preferred default, so permit uninstall only when
+                // there is more than one candidate
+                enabled = (mHomePackages.size() > 1);
+            } else {
+                // There is an explicit default home app -- forbid uninstall of
+                // that one, but permit it for installed-but-inactive ones.
+                enabled = !mPackageInfo.packageName.equals(currentDefaultHome.getPackageName());
+            }
+        }
+
         mUninstallButton.setEnabled(enabled);
         if (enabled) {
             // Register listener