Question

I am developing an application that needs to pair with other devices through Bluetooth. I was having trouble in order to show the list of paired devices in correct manner. I had also viewed the example in the android api (Bluetooth Chat), but i was having the same problem.

The list of paired devices are to big and then hides a search button that are at the bottom of the list.

My xml code is very the same of the example:

<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  >
  <TextView android:id="@+id/listpaired_devices"
        android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/title_paired_devices"
    android:visibility="gone"
    android:background="#666"
    android:textColor="#fff"
    android:paddingLeft="5dp" 
  /> 
  <ListView android:id="@+id/paired_devices"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:stackFromBottom="true"
    android:layout_weight="1"
  />
  <TextView android:id="@+id/list_new_devices"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/title_other_devices"
    android:visibility="gone"
  /> 
  <ListView android:id="@+id/new_devices"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:stackFromBottom="true"
    android:layout_weight="2" 
  />  
  <Button android:id="@+id/btscan"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/btscan"
  />
</LinearLayout>

But and i can’t show the search button at the bottom.
Here my screen:
My Screen

You could see a bit of the button at the bottom of the dialog window.

It’s possible to limit the number of rows shown at the listview ? Can anyone tell me how i can fix this problem

Answer 1

Firstly some points about your code:

• layout_weight is only meaningful if an object has no size in a certain dimension, that is you set layout_height or layout_width to 0, so this has no effect on your code.
• Setting the height of a ListView to wrap_content is pretty meaningless, and even if it works it’s bad practice. Use either ‘fill_parent’ or a definite height.
• The button is hidden because, as per the point above, the ListViews you have created have no predefined size so take up as much space as they can, pushing the button off the screen.

So let’s think about what you really have there – it’s just a single list with a button at the bottom (yes you may have headers or multiple sources of data in there but we’ll get onto that).

The following layout will give you a ListView at the top and a Button at the bottom. The ListView will take up any space not being used by the Button. Notice how the Button is defined before the ListView in the layout – this causes Android to calculate how much height the button takes up before considering the ListView. It then gives the ListView the rest of the height available.

<RelativeLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  >
  <Button android:id="@+id/btscan"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:text="@string/btscan"
  />
  <ListView android:id="@+id/all_devices"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_above="@id/btscan"
    android:stackFromBottom="true"
  />  
</RelativeLayout>

So that’s the layout. Now lets consider the actual content of your list: you have a header, followed by a list of paired devices, followed by another header and then a list of new devices.

You can create this using a single Adapter – Commonsware provides a very good implementation called MergeAdapter but you could code your own. MergeAdapter doesn’t directly let you a view (e.g. for the headers) but thankfully Commonsware also provides the SackOfViewsAdapter which allows you to add views to it, and then you can add the SackOfViewsAdapter to the MergeAdapter.

Here is some pseudo-code which should accomplish what is outlined above.

// This is the adapter we will use for our list with ListView.setAdapter
MergeAdapter listAdapter = new MergeAdapter();

// The first header - you'll need to inflate the actual View (myHeaderView1) from some resource
// using LayoutInflater
List<View> firstHeaderViews = new List<View();
firstHeaderViews.add(myHeaderView1);
SackOfViewsAdapter firstHeaderAdapter = new SackOfViewsAdapter(firstHeaderViews)

// Second header
List<View> secondHeaderViews = new List<View();
secondHeaderViews.add(myHeaderView2);
SackOfViewsAdapter secondHeaderAdapter = new SackOfViewsAdapter(secondHeaderViews);

// Now to add everything to the MergeAdapter

// First goes the first header
listAdapter.addAdapter(firstHeaderAdapter);

// Now your first list
listAdapter.addAdapter(firstListAdapter);

// Now your second header
listAdapter.addAdapter(secondHeaderAdapter);

// Now your second list
listAdapter.addAdapter(secondListAdapter);

// Now set the adapter to the list
myList.setAdapter(listAdapter)

The layout produced should look something like this. Note I extended the list to show how it behaves with a list longer than the screen; the button still remains visible. The red box marks the bounds of the screen.