When I create a class extends BaseAdapter, I get a warning message
Unconditional layout inflation from view adapter: Should use View Holder pattern (use recycled view passed into this method as the second parameter) for smoother scrolling
Do I need to change my code like this suggestion? All my code is running smoothly, it's just whether it is necessary to change the code to do updata code with the latest styles? Or just need to add #SuppressLint({ "ViewHolder", "InflateParams" }) ?
My adapter
public View getView(int position, View convertView, ViewGroup parent) {
View v = inflater.inflate(R.layout.list_item, null);
TextView merchant_type = (TextView) v.findViewById(R.id.merchant_type);
TextView merchant_name = (TextView) v.findViewById(R.id.merchant_name);
TextView merchant_location = (TextView) v.findViewById(R.id.merchant_location);
VoucherBean obj = (VoucherBean) getItem(position);
merchant_type.setText(obj.getMerchantType());
merchant_name.setText(obj.getMerchantName());
merchant_location.setText(obj.getMerchantLocation());
return v;
}
If you want to change my code as recommended above warning, like what my code later? Sorry if my question is too basic for a beginner
if you have more data in your list view then you should use recycling, because it improves scrolling and performance also. here is code look like if you use view holder in your adapter.
your ViewHolder looks like
public class ViewHolder {
public TextView merchant_type;
public TextView merchant_name;
public TextView merchant_location;
}
and your getView method
View vi = convertView;
ViewHolder holder;
if (convertView == null) {
vi = inflater.inflate(R.layout.list_item, null);
holder = new ViewHolder();
holder.merchant_type = (TextView) vi.findViewById(R.id.merchant_type);
holder.merchant_name = (TextView) vi.findViewById(R.id.merchant_name);
holder.merchant_location = (TextView) vi.findViewById(R.id.merchant_location);
vi.setTag(holder);
} else
holder = (ViewHolder) vi.getTag();
// now set your text view here like
holder.merchant_name.setText("Bla Bla Bla");
// return your view
return vi;
The View Holder pattern is meant to make your code easier to read and to maintain. If you look at the standard ViewHolder you'll see that its a class that basically does what you do in your getView:
private static class ExampleViewHolder{
TextView merchant_type;
TextView merchant_name;
TextView merchant_location;
public ExampleViewHolder(View view){
merchant_type = (TextView) v.findViewById(R.id.merchant_type);
merchant_name = (TextView) v.findViewById(R.id.merchant_name);
merchant_location = (TextView) v.findViewById(R.id.merchant_location);
}
}
Then in your getView method you'd get your view like this:
ExampleViewHolder holder = new ExampleViewHolder(view);
view.setTag(holder);
It's good to have them and the newer apis kind of force the use of this pattern, however as you can see by the code it doesn't change much besides readability and ease of maintenance.
However! There is an important part of the getView method that you are missing, and is most likely the reason for the warning.
The listview recycles the views, and gives them back to the adapter so that the same view doesnt have to be inflated everytime. Saves resources and a lot of memory, and you're not making use of this very important aspect of the listView.
You see, the way it recycles views is passing the old view, that you inflated before, back to the adapter through the convertView, so if the convertView is not null you can be sure its the inflated layout that you are using. So use that instead of inflating a new one:
View view = convertView;
ExampleViewHolder holder;
if(view == null){//means convertView is also null
view = inflater.inflate(yourlayout, parent, false);
holder = new ExampleViewHolder(view);
view.setTag(holder);
}else{
holder = (ExampleViewHolder) view.getTag();
}
Related
I'm trying to create a simple chat/message layout. My problem is with the Adapter. I want to use two different layouts. One for outgoing and one incoming messages. Furthermore I would like to use the ViewHolder approach. But my implementation causes the same layout to be inflated/reused everytime getView runs.
Can anyone please explain to me why this is happening? Do I need to use two viewholders?
The relevant code is shown below
#Override
public View getView(int position, View convertView, ViewGroup parent) {
int direction = getItemViewType(position);
ViewHolder holder;
if (convertView == null) {
int res = 0;
int resid = 0;
holder = new ViewHolder();
if (direction == DIRECTION_INCOMING) {
holder = new ViewHolder();
res = R.layout.message_l_box;
resid = R.id.left_bubble_text;
}
else {
res = R.layout.message_r_box;
resid = R.id.right_bubble_text;
}
convertView = LayoutInflater.from(mContext).inflate(res, parent, false);
holder.text = (TextView) convertView.findViewById(resid);
convertView.setTag(holder);
}
else {
holder = (ViewHolder) convertView.getTag();
}
holder.text.setText(getItem(position).first);
return convertView;
}
// Ensure that find by id is not called every time -> could cause slow scrolling
private class ViewHolder {
TextView text;
}
ListViews reuse Views when possible for performance. That is what the convertView View in your code is for. If Android already had another row that you scrolled away from it can be reused so it will be passed into your getView() method. Your code is not creating a new layout if convertView is not null.
You could do something like this, basically store the current layouts direction in the ViewHolder so you know if you can reuse the layout or have to re-inflate it.
private class ViewHolder {
TextView text;
int direction;
}
if (convertView == null || ((ViewHolder) convertView.getTag()).direction != direction) {
// same code you have now to layout a new row
holder.direction = direction
} else { // we know the existing view has same direction so it has the correct layout already inflated and we can reuse it
holder = (ViewHolder) convertView.getTag();
}
I am trying to implement a Newsfeed-type layout with multiple feed items.
The newsfeed item would have a certain layout when collapsed, and this layout would be replaced by an 'exploded' version, when the item is clicked.
I accomplished this by using a ListView of custom items. The custom item XML layout file has a ViewStub which is what I used to change the layout back and forth.
Now, though, I wanted to 'migrate' the layout over to RecyclerView, and to also follow a ViewHolder design pattern.
The latter is what I have tried first, and I'm running into all sorts of problems.
My approach has been as follows:
Get reference to collapsed layout (events_list_item_content) and expanded layout (events_list_item_selected_content);
Get reference to a simple layout resource file to be set as the ViewStub layout (view_stub_layout).
Get ViewStub reference, set its layout (view_stub_layout) inflate, and add the collapsed layout view to this layout (when first creating the feed, all of its items are going to be collapsed).
(After initialisation, when an item is clicked) Remove previous view (layout) from the ViewStubLayout, add the other type of layout.
Here is my custom adapter class:
public class FeedRecyclerAdapter extends BaseAdapter {
public class ViewHolder {
View inflatedViewStub1;
ViewStub viewStub;
LinearLayout viewStubLayout;
LinearLayout listItemContent, listItemContentSelected;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if (inflater == null)
inflater = (LayoutInflater) activity
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
final FeedItem item = feedItems.get(position);
final ViewHolder viewHolder;
if (convertView == null) {
viewHolder = new ViewHolder();
convertView = inflater.inflate(R.layout.events_list_item_content_new_container, parent, false);
View view = null;
view = inflater.inflate(R.layout.events_list_item_content, null);
viewHolder.listItemContent = (LinearLayout) view.findViewById(R.id.events_list_item_content);
view = inflater.inflate(R.layout.events_list_item_selected_content, null);
viewHolder.listItemContentSelected = (LinearLayout) view.findViewById(R.id.events_list_item_content_selected);
view = inflater.inflate(R.layout.view_stub_layout, null);
viewHolder.viewStubLayout = (LinearLayout) view.findViewById(R.id.view_stub_layout);
viewHolder.viewStub = (ViewStub) convertView.findViewById(R.id.list_item_feed);
(viewHolder.viewStubLayout).addView(viewHolder.listItemContent);
viewHolder.viewStub.setLayoutResource(R.layout.view_stub_layout);
viewHolder.inflatedViewStub1 = viewHolder.viewStub.inflate();
convertView.setTag(viewHolder);
} else viewHolder = (ViewHolder) convertView.getTag();
if (item.getExploded()) {
viewHolder.viewStubLayout.removeAllViews();
viewHolder.viewStubLayout.addView(viewHolder.listItemContentSelected);
} else {
viewHolder.viewStubLayout.removeAllViews();
viewHolder.viewStubLayout.addView(viewHolder.listItemContent);
}
return convertView;
}
However, when testing, the page where the Newsfeed is supposed to appear is blank.
ViewStub stub = (ViewStub) findViewById(R.id.layout_stub);
LinearLayout ll = (LinearLayout) findViewById(R.id.ll);
stub.setLayoutResource(layoutId);
stub.inflate(); // inflate 1st layout
ll.removeAllViews(); // remove previous view, add 2nd layout
ll.addView(LayoutInflater.from(context).inflate(secondLayoutId, ll, false));
Android ViewStub change layouts programatically
I know that many similar questions have been posted on stackoverflow, so please don't think I haven't searched high and low. I think my problems simply comes from now completely understanding listViews and the lifecycles of list items. I have a list view that can contain two types of messages, outbound or inbound. Originally, my listView would use a different background color depending on the type of message (outbound vs inbound), and it worked flawlessly. Now my application doesn't require a different background for list items, but it actually requires different layouts for different list items.
This is a clip of my Adapter.
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;
SoapBoxMessage thisMessage = messages.get(position);
if (v == null) {
LayoutInflater inflater = (LayoutInflater) getContext()
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (thisMessage.isOutbound()) {
v = inflater.inflate(R.layout.outbound_row, null);
} else {
v = inflater.inflate(R.layout.inbound_row, null);
}
}
Adapters can support different ViewItemTypes that will solve your recycling problems.
static public enum LAYOUT_TYPE {
INBOUND,
OUTBOUND
}
#Override
public int getViewTypeCount () {
return LAYOUT_TYPE.values().length;
}
#Override
public int getItemViewType (int position) {
if ( messages.get(position).isOutbound())
return LAYOUT_TYPE.OUTBOUND.ordinal();
else
return LAYOUT_TYPE.INBOUND.ordinal();
}
#Override
public View getView (int position, View convertView, ViewGroup parent) {
LAYOUT_TYPE itemType = LAYOUT_TYPE.values()[getItemViewType(position)];
... (code until inflater )
switch (itemType){
case INBOUND:
convertview = /inflate & configure inbound layout
break;
case OUTBOUND:
convertview = /inflate & configure outbound layout
break;
}
you don't need to worry about recycling views because the listview will respect the ViewItemTypes for each position and it will only provide a convertview of the correct viewtype for that position
The problem is that listview is recycling the view so when you check if the view is null it wont pass that because the view is not null when it is recycled
you would need to inflate the view each time getView is called, basically removing if(v == null)
Try to use a ViewHolder like this:
ViewHolder holder;
public View getView(int position, View convertView, ViewGroup parent) {
convertView = null;
SoapBoxMessage thisMessage = messages.get(position);
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (thisMessage.isOutbound()) {
convertView = inflater.inflate(R.layout.outbound, null, false);
//specific to your outbound layout
holder = new ViewHolder();
holder.text= (TextView)convertView.findViewById(R.id.textview);
holder.group = (RadioGroup)convertView.findViewById(R.id.toggleGroup);
holder.toggle = (ToggleButton)convertView.findViewById(R.id.toggleButton);
} else {
convertView = inflater.inflate(R.layout.inbound, null, false);
//specific to your inbound layout
holder = new ViewHolder();
holder.text= (TextView)convertView.findViewById(R.id.textview);
holder.group = (RadioGroup)convertView.findViewById(R.id.toggleGroup);
holder.toggle = (ToggleButton)convertView.findViewById(R.id.toggleButton);
}
convertView.setTag(holder);
}
else{
holder = (ViewHolder) convertView.getTag();
}
//Here you can set the text or other code you want to implement
holder.text.setText("Whatever!");
return convertView;
}
static class ViewHolder {
//TODO put components you use like:
TextView text;
RadioGroup group;
ToggleButton toggle;
}
It's because of the recycling that is happening. You would need something along these lines:
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
SoapBoxMessage thisMessage = messages.get(position);
if (convertView == null) {
LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
convertView = mInflater.inflate(R.layout.listview_feedlog_item, null);
holder = new ViewHolder();
holder.txtTime = (TextView) convertView.findViewById(R.id.textTime);
holder.txtDate = (TextView) convertView.findViewById(R.id.textDate);
convertView.setTag(holder);
} else
holder = (ViewHolder) convertView.getTag();
// I don't know how your SoapBoxMessage is made up so here are two sample methods
holder.txtTime.setText(thisMessage.getTime());
holder.txtDate.setText(thisMessage.getDate());
return convertView;
}
/* private view holder class */
private class ViewHolder {
TextView txtTime;
TextView txtDate;
}
Also, remember to always reset or initiate a value in the getView method. Since a View can be recycled it might carry with it properties of its former life.
Whether this is a good practice or not, Removing if (v == null) will solve the problem.
Anyway, you will have to re-inflate the view.
Hi i'm having this kind of problem, when scrolling imageviews change their positions and
their background images. I saw other answers on this topic on this site, but non of them
helped me.
Like this once:
grid view scrolling issue
GridView scrolling problem on Android
GridView elements changes their place dynamically when scroll screen
and many others...but they don't solve my problem.
Important thing is that i don't use custom layout for gridview or gridview items(imageViews).I create them programmatically. This is very important to me so if someone know the answer pls help me...Thanks.
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView==null){
imageView = new ImageView(ctx);
} else {
imageView = (ImageView) convertView;
}
imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
imageView.setBackgroundResource(tmp[position]);
imageView.setImageResource(blank);
return imageView;
}
Its a simple method. Adapters recycle each and every view while scrolling. So we just need to create the ones which are being re-used after the first time. Holders help to avoid expensive calls like findViewById and re-use the items by just getting the old ones and changing its properties.
One point you need to keep in mind is that we need to hold the images which are to be displayed in any one of the containers like array[] or List and reset each time before returning the view, or else it will display the previously last recycled view.
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
LayoutInflater inflater = (LayoutInflater) activity
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null) {
convertView = inflater.inflate(R.layout.item_layout, null);
holder = new ViewHolder();
holder.cover = (ImageView) convertView
.findViewById(R.id.item_cover);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.cover.setBackgroundResource(tmp[position]);
return convertView ;
}
static class ViewHolder {
ImageView cover;
}
try this
class Holder {
ImageView imageView;
}
public View getView(int position, View convertView, ViewGroup parent) {
Holder holder;
if(holder.imageView==null){
holder=new Holder();
holder.imageView = new ImageView(ctx);
holder.imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
holder.imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
holder.imageView.setPadding(8, 8, 8, 8);
imageView.setTag(holder);
} else {
holder= (Holder) imageView.getTag();
}
holder.imageView.setBackgroundResource(tmp[position]);
holder.imageView.setImageResource(blank);
return imageView;
}
I have a listview that uses a customadapter based on the baseadapter. The listview populates ok using external data and I can pick up the click events and know which item has been selected.
I'm having a problem updating the clicked item's views, like TextView and ViewFlipper.
Do I have to update something via the listview or is it via the adapter. I've tried things like the following;
View test = (View)adapter.getView(pos, null, myListView);
ViewFlipper temp = (ViewFlipper)test.findViewById(R.id.flipholder);
temp.showNext();
TextView temp2 = (TextView)test.findViewById(R.id.filmtitle);
temp2.setText("Hello World");
Which results in the viewfliper flipping the first and third item or second and fourth and the text not updating at all.
Any ideas?
Cheers
Try this pattern in getView:
public View getView(int position, View convertView, ViewGroup parent) {
// A ViewHolder keeps references to children views to avoid unneccessary calls
// to findViewById() on each row.
ViewHolder holder;
// When convertView is not null, we can reuse it directly, there is no need
// to reinflate it. We only inflate a new View when the convertView supplied
// by ListView is null.
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_item_icon_text, null);
// Creates a ViewHolder and store references to the two children views
// we want to bind data to.
holder = new ViewHolder();
holder.text = (TextView) convertView.findViewById(R.id.text);
holder.icon = (ImageView) convertView.findViewById(R.id.icon);
convertView.setTag(holder);
} else {
// Get the ViewHolder back to get fast access to the TextView
// and the ImageView.
holder = (ViewHolder) convertView.getTag();
}
// Bind the data efficiently with the holder.
holder.text.setText(DATA[position]);
holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);
return convertView;
}
static class ViewHolder {
TextView text;
ImageView icon;
}
}