add ios alert box example

README.md

@@ -20,6 +20,7 @@
  - [Await for specific module to load](#await-for-condition)
  - [Android make Toast](#android-make-toast)
  - [Hook java io InputStream](#hook-java-io-inputstream)
+ - [iOS alert box](#ios-alert-box)
  - [TODO list](#todos)
 
 #### Intercept and backtrace low level open
@@ -455,7 +456,21 @@ function hookInputStream() {
 Java.perform(hookInputStream);
 ```
 
+#### iOS alert box
+```
+var UIAlertController = ObjC.classes.UIAlertController;
+var UIAlertAction = ObjC.classes.UIAlertAction;
+var UIApplication = ObjC.classes.UIApplication;
+var handler = new ObjC.Block({ retType: 'void', argTypes: ['object'], implementation: function () {} });
 
+ObjC.schedule(ObjC.mainQueue, function () {
+  var alert = UIAlertController.alertControllerWithTitle_message_preferredStyle_('Frida', 'Hello from Frida', 1);
+  var defaultAction = UIAlertAction.actionWithTitle_style_handler_('OK', 0, handler);
+  alert.addAction_(defaultAction);
+  // Instead of using `ObjC.choose()` and looking for UIViewController instances on the heap, we have direct access through UIApplication:
+  UIApplication.sharedApplication().keyWindow().rootViewController().presentViewController_animated_completion_(alert, true, NULL);
+})
+```