Chapter 8 - Adding a GUI

Here are the steps to take to add a GUI such as a button to your NDK application:

in the res/layout/*.xml file create a button using the Android Studio drag and drop tool
- In the properties section in the right give your item a good ID name.
- You can also change other useful information such as the text displayed.
You can set your onClick in the Main Activity programmatically or just set the onClick in the properties of the GUI.
- NOTE: you need to have a function first in your main activity.
Create the function in your main activity
- example - public void snapShot(View view) { }
- NOTE: I have found from others that a better way of getting the click is using a findViewById(R.id.snapshot).setOnClickListener(this); call after setContentView()
  - This way lets you have one function to switch case the buttons.
  - @Override public void onClick(View v) { // Handle button clicks. switch (v.getId()) { ... ... } }
Now add a call to you JNI Native class.
- public void snapShot(View view) { TangoJNINative.snapShot(1); }
In you JNI Native file add the new function:
- public static native void snapShot();
In the JNI_Header add if you are not auto generating it:
- Java_com_demo_tutorial_tango_tango_1ndk_1tutorial_TangoJNINative_snapShot(JNIEnv*, jobject, int type)) { app.snapShot(type); }
Add the function to you native code.
- Don't forget to declare it in your header file if needed.
- void myApp::snapShot(int type) { // cool stuff }

Conclusion

To send data from a GUI element to your native code you need to: