To Examples

MonthButtons2 Example

Goal

• Use a ScrollView to display 12 buttons, one for each month.
  However, for this example, add the buttons dynamically in the activity code.
  Also add the event handlers as anonymous methods in the activity code.

Directions

1. Create a project named MonthButtons2.  Leave the layout and activity files with their default names.
2. Change the layout to LinearLayout and place it in a ScrollView like this:
   

   <ScrollView
       xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:app="http://schemas.android.com/apk/res-auto"
       xmlns:tools="http://schemas.android.com/tools"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       tools:context=".MainActivity">
   
      <LinearLayout
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation="vertical">
      </LinearLayout>
   </ScrollView>
   

3. Add the id linear_layout to the linear layout:
   

   android:id="@+id/linear_layout"
   

4. Add this code to OnCreate method of the activity code file:
   

    // The layout and buttons are declared as 
   // final because they are referenced in the
   // event handler in the inner class.
   final LinearLayout layout = (LinearLayout)
   findViewById(R.id.linear_layout);
   LinearLayout.LayoutParams params =
       new LinearLayout.LayoutParams(
           LayoutParams.MATCH_PARENT,
           LayoutParams.MATCH_PARENT);
   
   //CharSequence[ ] months = {
   String[ ] months = {
       "January ", "February", "March ", "April ", "May ", 
       "June ", "July ", "August ", "September",
       "October ", "November", "December "};
   
   for (int i = 1; i <= 12; i++) {
       final Button btn = new Button(this);
       btn.setId(i);
       btn.setText(months[i - 1]);
       btn.setLayoutParams(params);
       layout.addView(btn);
   }

5. Run your app to test it.
6. Add this code at the end of the for loop to add event handlers to all of the buttons.
   

   btn.setOnClickListener(new View.OnClickListener( ) {
       public void onClick(View v) {
           Button b =(Button) v;
           String label = b.getText( ).toString( );
           System.out.println("Text: " + label);
           Toast toast = Toast.makeText(
               getApplicationContext(),
               "Clicked Button:" + label,
               Toast.LENGTH_LONG);
           toast.show( );
       }
   });
   

7. Run the app again to test it. Here is the emulator screenshot.
8. Here are the final files for the layout and activity:
       activity_main.xml   MainActivity.java