If you wish to be an Android developer, it is not enough just porting ROMs to your device. You must also know how to edit APK files. If you are on the PC, I recommend you to use APK Multi tool which is perhaps the best tool I have come across to edit APK files. But if you wish to do it on the phone, you will need an app. NinjaMorph is one such app which lets you edit APK files right from your Android phone.
To begin editing, install Ninjamorph application on your phone from the link at the end of the post. You will need to have a rooted device to use Ninjamorph since you are editing system files. Hence you need to provide the app with Suepruser application to begin the hacking of your system files.
A wonderful thread on XDA Forums shows how to use the tool. An example of the changes that can be done using this tool can be seen in the image below:
That is the icon used to show the signal strength on your phone. It is only an image. There are different images to denote different signal levels. So when the strength of the signal changes, the images used for it also changed. To edit it, you need to replace the image that is used for this purpose.
How To Use NinjaMorph to Edit APK files?
The APK file is a compressed form of images, smali files and xml files. To edit your APK, you need to extract all these files from the APK file.
In other words, you need to decompile the APK file which will result in all these files being extracted. Ninjamorph does the job of decompiling the files and lets you replace the images with those which you already have on your phone.
So before you proceed with editing, you need to decide which system APK you wish to edit and you should also have a new image which will be used to replace with the one that is in the system.
For instance, if I wish to edit the image used to denote the signal strength as shown in the image above, I need to edit SystemUI.apk which is present in /system/app folder. All system apps are present in the same folder.
After you install Ninjamorph, open the application and tap on “New Project” to select the APK file you wish to edit.
It will extract the contents of the APK file after which you will see some xml files, folders like META-INF and res.
To replace images, you need to open res folder and the open the drawable-mdpi. Depending on your device, it may also be drawable-ldpi. This folder is present in almost all APK files. This folder contains all the images that the app uses.
Tap on the image and then replace it with another image already present on your SD card. Make sure you keep the dimensions of the image same as it is in the system APK. Replace it and recompile it. The APK will now be modified.
To know more about this, you can watch the following videos: