46. ​​ExpandableListView Events

In this lesson:

- we process events of the tree list

We are able to build a tree-list, now let's see how we can interact with it. We are given the opportunity to handle the following events: clicking on a group, clicking on an element, collapsing a group, expanding a group.

Let's create   project :

Project name : P0461_ExpandableListEvents
Build Target : Android 2.3.3
Application name : ExpandableListEvents
Package name : ru.startandroid.develop.p0461expandablelistevents
Create Activity : MainActivity

Screen main.xml :

  <? xml version = "1.0" encoding = "utf-8"?> 
  <LinearLayout 
  xmlns: android = "http://schemas.android.com/apk/res/android" 
  android: layout_width = "fill_parent" 
  android: layout_height = "fill_parent" 
  android: orientation = "vertical"> 
  <LinearLayout 
  android: id = "@ + id / linearLayout1" 
  android: layout_width = "match_parent" 
  android: layout_height = "wrap_content" 
  android: orientation = "vertical"> 
  <Textview 
  android: id = "@ + id / tvInfo" 
  android: layout_width = "wrap_content" 
  android: layout_height = "wrap_content"> 
  </ TextView> 
  <ExpandableListView 
  android: id = "@ + id / elvMain" 
  android: layout_width = "match_parent" 
  android: layout_height = "wrap_content"> 
  </ ExpandableListView> 
  </ LinearLayout> 
  </ LinearLayout> 

TextView to display information and ExpandableListView .

In the project, next to the MainActivity class, we will create (not an Activity) the AdapterHelper class. Put the code in it to fill the list in order to unload MainActivity.java.

AdapterHelper.java code:

The code for creating an adapter is completely borrowed from the last lesson. To get the adapter, we just need to call the getAdapter method.

The class has a constructor through which we give the object a link to the context . Context we need to create an adapter. The adapter, in turn, needs context, for example, to access the LayoutInflater.

At the end of the class are methods that return us the names of groups and elements from collections by group number or element number. To do this, use the getGroup and getChild adapter methods, bring them to the Map and retrieve the value of the attribute with the name of the company or phone.

We write the code in MainActivity.java :

Thanks to the AdapterHelper class, the adapter creation code took only two lines: the creation of an object and a call to the getAdapter method. Next, assign the adapter to the list and add handlers :

1) OnChildClickListener - click on the item

Method
public boolean onChildClick (ExpandableListView parent, View v, int groupPosition, int childPosition, long id), where

parent - ExpandableListView with which we work
v - View element
groupPosition - group position in the list
childPosition - the position of the element in the group
id - element id

We log the position and id. And in the TextView at the top of the list, we display the text of the clicked element and its group , which we obtain using the AdapterHelper methods.

The method should return boolean . If we return true - it means, we inform that we ourselves have fully processed the event and it will not go to further event handlers (if any). Returning false means we allow the event to go further .

2) OnGroupClickListener - clicking on a group

Method
public boolean onGroupClick (ExpandableListView parent, View v, int groupPosition, long id), where

parent - ExpandableListView with which we work
v - View element
groupPosition - group position in the list
id - group id

We log the position and id of the group.

This method should also return boolean . We will return true if the position of the group = 1, otherwise - false. Those. for this group, we block further event handling. Further we will see that it will give us.

3) OnGroupCollapseListener - folding group

Method
onGroupCollapse (int groupPosition), where groupPosition is the position of the group that is collapsed

4) OnGroupExpandListener - group deployment

Method
onGroupExpand (int groupPosition), where groupPosition is the position of the group that has been expanded

And at the end of the MainActivity code, we expand the group with position 2 using the expandGroup method.

All save and run.

As you can see, the LG group is immediately deployed. This worked for the expandGroup command at the end of the code.

If you look in the log, we see

onGroupExpand groupPosition = 2

Those. fulfilled the event of expanding the group with position 2.

Click, for example, on Optimus Link. We look at the log:

onChildClick groupPosition = 2 childPosition = 1 id = 1

Do not forget that the position is considered from scratch. Group with position 2 - LG, element with position 1 - Optimus Link, that's right.

We look at the TextView at the top of the screen, it read the attribute value from the adapter and displayed it.

Now let's try to minimize the LG group, click on it. We look at the log:

onGroupClick groupPosition = 2 id = 2
onGroupCollapse groupPosition = 2

First worked onGroupClick - clicking on the group, and then onGroupCollapse - folding the group. TextView at the top of the screen announced that the LG group had collapsed.

Expand the LG group again. Log:

onGroupClick groupPosition = 2 id = 2
onGroupExpand groupPosition = 2

Clicking on a group and unfolding. Please note that during software deployment, there was no push event, only a reversal.

Now let's try to expand the group with position 1 - Samsung. The group does not unfold. We look at the log:

onGroupClick   groupPosition = 1 id = 1

There is a push event, but the deployment handler is not called. This is because of the line

For the group with position 1, we block further event handling and it does not go to the expand or collapse handlers. Therefore, onGroupExpand does not work.

As a result, these 4 handlers allow you to determine how the user interacts with the tree.