O'Reilly 9781449388416 Datasheet download pdf (Page 67)

Example 1-10. Code snippet 4 of /src/com/examples/tipcalc/Tipster.java

* Attach a KeyListener to the Tip Amount, No. of People and Other Tip

* Percentage text fields

txtAmount.setOnKeyListener(mKeyListener);

txtPeople.setOnKeyListener(mKeyListener);

txtTipOther.setOnKeyListener(mKeyListener);

Notice that we create just one listener instead of creating anonymous/inner listeners

for each text field. I am not sure if my style is better or recommended, but I always write

in this style if the listeners are going to perform some common actions. Here the com-

mon concern for all the text fields is that they should not be empty, and only when they

have values should the Calculate button be enabled.

Example 1-11. Code snippet 5 from KeyListener.java

* KeyListener for the Total Amount, No of People and Other Tip Percentage

* text fields. We need to apply this key listener to check for the following

* conditions:

* 1) If the user selects Other Tip Percentage, then the Other Tip Percentage text field

* should have a valid tip percentage entered by the user. Enable the

* Calculate button only when the user enters a valid value.

* 2) If the user does not enter values in the Total Amount and No. of People fields,

* we cannot perform the calculations. Hence we enable the Calculate button

* only when the user enters valid values.

private OnKeyListener mKeyListener = new OnKeyListener() {

@Override

public boolean onKey(View v, int keyCode, KeyEvent event) {

switch (v.getId()) {

case R.id.txtAmount:

case R.id.txtPeople:

btnCalculate.setEnabled(txtAmount.getText().length() > 0

&& txtPeople.getText().length() > 0);

break;

case R.id.txtTipOther:

btnCalculate.setEnabled(txtAmount.getText().length() > 0

&& txtPeople.getText().length() > 0

&& txtTipOther.getText().length() > 0);

break;

}

return false;

}

};

1.15 Program: Tipster, a Tip Calculator for the Android OS | 55

1 2 ... 62 63 64 65 66 67 68 69 70 71 72 73 74

No comments

O'Reilly 9781449388416 Datasheet Page 67