Mark Murphy - Beginning Android

To find out when a context-menu choice was selected, implement onContextItemSelected()on the activity. Note that you get only the MenuIteminstance that was chosen in this callback. As a result, if your activity has two or more context menus, you may want to ensure they have unique menu-item identifiers for all their choices so you can tell them apart in this callback. Also, you can call getMenuInfo()on the MenuItemto get the ContextMenu.ContextMenuInfoyou received in onCreateContextMenu(). Otherwise, this callback behaves the same as onOptionsItemSelected(), described in the previous section.

In the sample project Menus/Menusat http://apress.com/, you will find an amended version of the ListViewsample ( List) with an associated menu. Since the menus are defined in Java code, the XML layout need not change and is not reprinted here.

However, the Java code has a few new behaviors, as shown here:

public classMenuDemo extendsListActivity {

TextView selection;

String[] items={"lorem", "ipsum", "dolor", "sit", "amet",

"consectetuer", "adipiscing", "elit", "morbi", "vel",

"ligula", "vitae", "arcu", "aliquet", "mollis",

"etiam", "vel", "erat", "placerat", "ante",

"porttitor", "sodales", "pellentesque", "augue", "purus"};

public static finalint EIGHT_ID = Menu.FIRST+1;

public static finalint SIXTEEN_ID = Menu.FIRST+2;

public static finalint TWENTY_FOUR_ID = Menu.FIRST+3;

public static finalint TWO_ID = Menu.FIRST+4;

public static finalint THIRTY_TWO_ID = Menu.FIRST+5;

public static finalint FORTY_ID = Menu.FIRST+6;

public static finalint ONE_ID = Menu.FIRST+7;

@Override

publicvoid onCreate(Bundle icicle) {

super. onCreate(icicle);

setContentView(R.layout.main);

setListAdapter( newArrayAdapter( this,

android.R.layout.simple_list_item_1, items));

selection = (TextView) findViewById(R.id.selection);

registerForContextMenu( getListView());

}

publicvoid onListItemClick(ListView parent, View v,

int position, long id) {

selection. setText(items[position]);

}

@Override

publicvoid onCreateContextMenu(ContextMenu menu, View v,

ContextMenu.ContextMenuInfo menuInfo) {

populateMenu(menu);

}

@Override

publicboolean onCreateOptionsMenu(Menu menu) {

populateMenu(menu);

return( super. onCreateOptionsMenu(menu));

}

@Override

publicboolean onOptionsItemSelected(MenuItem item) {

return( applyMenuChoice(item) ||

super. onOptionsItemSelected(item));

}

@Override

publicboolean onContextItemSelected(MenuItem item) {

return( applyMenuChoice(item) ||

super. onContextItemSelected(item));

}

privatevoid populateMenu(Menu menu) {

menu. add(Menu.NONE, ONE_ID, Menu.NONE, "1 Pixel");

menu. add(Menu.NONE, TWO_ID, Menu.NONE, "2 Pixels");

menu. add(Menu.NONE, EIGHT_ID, Menu.NONE, "8 Pixels");

menu. add(Menu.NONE, SIXTEEN_ID, Menu.NONE, "16 Pixels");

menu. add(Menu.NONE, TWENTY_FOUR_ID, Menu.NONE, "24 Pixels");

menu. add(Menu.NONE, THIRTY_TWO_ID, Menu.NONE, "32 Pixels");

menu. add(Menu.NONE, FORTY_ID, Menu.NONE, "40 Pixels");

}

privateboolean applyMenuChoice(MenuItem item) {

switch(item. getItemId()) {

caseONE_ID:

getListView(). setDividerHeight(1);

return( true);

caseEIGHT_ID:

getListView(). setDividerHeight(8);

return( true);

caseSIXTEEN_ID:

getListView(). setDividerHeight(16);

return( true);

caseTWENTY_FOUR_ID:

getListView(). setDividerHeight(24);

return( true);

caseTWO_ID:

getListView(). setDividerHeight(2);

return( true);

caseTHIRTY_TWO_ID:

getListView(). setDividerHeight(32);

return( true);

caseFORTY_ID:

getListView(). setDividerHeight(40);

return( true);

}

return( false);

}

}

In onCreate(), we register our list widget as having a context menu, which we fill in via our populateMenu()private method, by way of onCreateContextMenu(). We also implement the onCreateOptionsMenu()callback, indicating that our activity also has an options menu. Once again, we delegate to populateMenu()to fill in the menu.

Our implementations of onOptionsItemSelected()(for options-menu selections) and onContextItemSelected()(for context-menu selections) both delegate to a private applyMenuChoice()method, plus chaining upwards to the superclass if none of our menu choices was the one selected by the user.

In populateMenu()we add seven menu choices, each with a unique identifier. Being lazy, we eschew the icons.

In applyMenuChoice()we see if any of our menu choices were chosen; if so, we set the list’s divider size to be the user-selected width.

Initially the activity looks the same in the emulator as it did for ListDemo(see Figure 11-1).

Figure 11-1. The MenuDemo sample application, as initially launched