where & how to use onKey,onkeyDown,onKeyPressed event in android?

hi where to use onKey and onKeyUp/Down event in android.

e.g. i have one textview . when user pressed any 开发者_Go百科key i want to display that character in textview, In this case which event(above) is used.

PLEASE explain with EXAMPLE 

Or give some other example that get the key event and print in edittext or some other.

Thanks in advance...

If you are looking this in EditText, its better to use these

editText.addTextChangedListener(new TextWatcher() {
                public void afterTextChanged(Editable s) { 
                    Log.v("TAG", "afterTextChanged");
                }

                public void beforeTextChanged(CharSequence arg0, int arg1, int arg2, int arg3) {
                    Log.v("TAG", "beforeTextChanged");
                }

                public void onTextChanged(CharSequence s, int start, int before, int count) {
                    Log.v("TAG", "onTextChanged");
                }
            });

pls refer the following code

public class Demo extends Activity
 {

    /**
     *  Variables & Objects Declaration
     * 
     */


     EditText  et;

     private static Context CONTEXT;
    /** Called when the activity is first created. */

    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
        setContentView(R.layout.main);
        et =(EditText)findViewById(R.id.header_text02);
        }// end of OnCreate

    @Override
    public boolean onKeyDown(View arg0, Editable arg1, int arg2, KeyEvent arg3) {
        // TODO Auto-generated method stub
        Log.v("I am ","KeyDown");
           switch (keyCode) {
                   case KeyEvent.KEYCODE_A:
                   {
                       //your Action code
                       et.setText("A");
                      return true;
                    }
                      case KeyEvent.KEYCODE_B:
                   {
                       //your Action code
                       et.setText("B");
                      return true;
                    }
                   // similarly write for others too
        }



        return true;
    }// End of onKeyDown



    @Override
    public boolean onKeyUp(View arg0, Editable arg1, int arg2, KeyEvent arg3) {
        // TODO Auto-generated method stub
        Log.v("I am ","KeyUp");
            et.setText("KeyUp");
        return true;
    }// End of onKeyUp



}