objective c - What is the right pattern for instantiating a device specific view controller in a Universal App? -

i'm new objective-c so, bear me. started universal app template in xcode4 , built application. there convention template starts off tried stick with. each view controller, there's main file , subclass each device type. example:

project/     exampleviewcontroller.(h|m)     - iphone/       - exampleviewcontroller_iphone.(h|m|xib)     - ipad/       - exampleviewcontroller_ipad.(h|m|xib) 

for part, pretty convenient. of logic goes in superclass , subclasses take care of device specific implementation.

here's part don't get. have code same thing in each subclass because need load different xib each device. example:

exampleviewcontroller_iphone

- (void)tableview:(uitableview *)tableview didselectrowatindexpath:(nsindexpath *)indexpath {     content *selectedcontent = (content *)[[self fetchedresultscontroller] objectatindexpath:indexpath];     contentdetailviewcontroller_iphone *detailviewcontroller = [[contentdetailviewcontroller_iphone alloc] init];     detailviewcontroller.content = selectedcontent;     detailviewcontroller.managedobjectcontext = self.managedobjectcontext;      [self.navigationcontroller pushviewcontroller:detailviewcontroller animated:yes];     [detailviewcontroller release]; } 

exampleviewcontroller_ipad

- (void)tableview:(uitableview *)tableview didselectrowatindexpath:(nsindexpath *)indexpath {     content *selectedcontent = (content *)[[self fetchedresultscontroller] objectatindexpath:indexpath];     contentdetailviewcontroller_ipad *detailviewcontroller = [[contentdetailviewcontroller_ipad alloc] init];     detailviewcontroller.content = selectedcontent;     detailviewcontroller.managedobjectcontext = self.managedobjectcontext;      [self.navigationcontroller pushviewcontroller:detailviewcontroller animated:yes];     [detailviewcontroller release]; } 

... notice in second instance thing different it's loading _ipad version of view controller. necessary because ipad , iphone view controllers attached separate, device specifc nibs.

what's "correct" pattern doing this?

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update

i found this answer loading separate xibs using device modifiers seems in case don't need specific subclass 1 device, still won't if need instantiate specific _iphone or _ipad instance of view controller device specific functionality.

there 2 simple ways solve problem. both work when placed in superclass.

the first method works because have 2 different classes, , 1 created depends on device being used. does not work if don't use different classes because there no device-specific code. involves asking object class decide is. since object's class device-specific class, when asked superclass, can check see class created , act accordingly.

- (void)tableview:(uitableview *)tableview didselectrowatindexpath:(nsindexpath *)indexpath {     content *selectedcontent = (content *)[[self fetchedresultscontroller] objectatindexpath:indexpath];     class classtouse;     if([self class] == [exampleviewcontroller_ipad class]) {         // running on ipad         classtouse = [contentdetailviewcontroller_ipad class];     } else {         // must running on either iphone or ipod touch         classtouse = [contentdetailviewcontroller_iphone class];     }     // use superclass typing here, since aren't doing device specific     contentdetailviewcontroller *detailviewcontroller = [[classtouse alloc] init];     detailviewcontroller.content = selectedcontent;     detailviewcontroller.managedobjectcontext = self.managedobjectcontext;      [self.navigationcontroller pushviewcontroller:detailviewcontroller animated:yes];     [detailviewcontroller release]; } 

the second method work in location in program. apple added property uidevice class in ios 3.2 called "user interface idiom". there 2 possible values: uiuserinterfaceidiompad , uiuserinterfaceidiomphone. since these don't exist in versions prior 3.2, apple added macro return uiuserinterfaceidiomphone if version less 3.2, , actual value uidevice object if greater or equal 3.2.

- (void)tableview:(uitableview *)tableview didselectrowatindexpath:(nsindexpath *)indexpath {     content *selectedcontent = (content *)[[self fetchedresultscontroller] objectatindexpath:indexpath];     class classtouse;     // if aren't supporting versions prior 3.2, can use [uidevice currentdevice].userinterfaceidiom instead save couple of cycles     if(ui_user_interface_idiom() == uiuserinterfaceidiompad) {         // running on ipad         classtouse = [contentdetailviewcontroller_ipad class];     } else {         // must running on either iphone or ipod touch         classtouse = [contentdetailviewcontroller_iphone class];     }     // use superclass typing here, since aren't doing device specific     contentdetailviewcontroller *detailviewcontroller = [[classtouse alloc] init];     detailviewcontroller.content = selectedcontent;     detailviewcontroller.managedobjectcontext = self.managedobjectcontext;      [self.navigationcontroller pushviewcontroller:detailviewcontroller animated:yes];     [detailviewcontroller release]; }