Am getting the following warning in Eclipse:
"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"
The code which i had used is:
class myadapter extends ArrayAdapter<String>
{
Context context;
int[] images;
String[] mytitle;
String[] mydescp;
myadapter(Context c, String[] tittle, int[] imgs, String[] desc)
{
super(c, R.layout.single_row, R.id.listView1, tittle);
this.context=c;
this.images=imgs;
this.mytitle= tittle;
this.mydescp=desc;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
LayoutInflater inflator = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View row = inflator.inflate(R.layout.single_row, parent, false);
ImageView myImage = (ImageView) row.findViewById(R.id.imageView1);
TextView myText = (TextView) row.findViewById(R.id.textView1);
TextView mydesc = (TextView) row.findViewById(R.id.textView2);
myImage.setImageResource(images[position]);
myText.setText(mytitle[position]);
mydesc.setText(mydescp[position]);
return row;
}
}
Am getting warning in the line : View row = inflator.inflate(R.layout.single_row, parent, false);
And it causes my android application to Force Close... What can i do it now??
Any Suggestions???
You need to recycle your views.What android as a system cares about is only the items that are visible.So you have to recycle the row items which are out of focus to be re-used for the newitems.
Or else imagine the amount of caching involved.
#Override
public View getView(int position, View row, ViewGroup parent) {
// TODO Auto-generated method stub
if(row==null){
LayoutInflater inflator = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row = inflator.inflate(R.layout.single_row, parent, false);
}
ImageView myImage = (ImageView) row.findViewById(R.id.imageView1);
TextView myText = (TextView) row.findViewById(R.id.textView1);
TextView mydesc = (TextView) row.findViewById(R.id.textView2);
myImage.setImageResource(images[position]);
myText.setText(mytitle[position]);
mydesc.setText(mydescp[position]);
return row;
}
You should re-use the view instead of inflating again and again. This brings down performance.
From your code,
View row = inflator.inflate(R.layout.single_row, parent, false);
this will inflate everytime when you scroll. To maximize the performance, use it like
//re-use
if (row == null)
{
inflate code here
}
else
{
you already have a view `row`, just use it.
}
You can see, for the first time row will be null & it will inflate and store it in View row. But, from the next time, it's not going to inflate again and again instead it will use the View row. (Re-use)
"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"
It's not the error it's just the warning for asking you to use ViewHolder Pattern. Let me explain you why it's important.
Without ViewHolder Pattern :
The first time it was loaded, convertView is null. We’ll have to inflate our list item layout and find the TextView via findViewById().
The second time it was loaded, convertView is not null, good! We don’t have to inflate it again. But we’ll use findViewById() again.
The following times it was loaded, convertView is definitely not null. But findViewById() is constantly called, it will work but, it slows down the performance especially if you have lots of items and Views in your ListView.
With the ViewHolder Design Pattern :
The first time it was loaded, convertView is null. We’ll have to inflate our list item layout, instantiate the ViewHolder, find the TextView via findViewById() and assign it to the ViewHolder, and set the ViewHolder as tag of convertView.
The second time it was loaded, convertView is not null, good! We don’t have to inflate it again. And here’s the sweet thing, we won’t have to call findViewById() since we can now access the TextView via its ViewHolder.
The following time it was loaded, convertView is definitely not null. The findViewById() is never called again, and that makes our smooth ListView scrolling.
Why to use?
Your code might call findViewById() frequently during the scrolling of ListView, which can slow down performance. Even when the Adapter returns an inflated view for recycling, you still need to look up the elements and update them. A way around repeated use of findViewById() is to use the view holder design pattern.
So, what is ViewHolder?
A ViewHolder object stores each of the component views inside the tag field of the Layout, so you can immediately access them without the need to look them up repeatedly. First, you need to create a class to hold your exact set of views.
How to use?
Make a separate class as ViewHolder & declare what you use like EditText,TextView etc..
static class ViewHolder {
TextView text;
TextView timestamp;
ImageView icon;
ProgressBar progress;
int position;
}
Then populate the ViewHolder and store it inside the layout.
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) { // if convertView is null
convertView = mInflater.inflate(R.layout.mylayout,
parent, false);
holder = new ViewHolder();
// initialize views
convertView.setTag(holder); // set tag on view
} else {
holder = (ViewHolder) convertView.getTag();
// if not null get tag
// no need to initialize
}
//update views here
return convertView;
}
Source :
Making ListView Scrolling Smooth from Android documentation
Android ViewHolder Pattern example
Hi Vinesh Senthilvel ,
Don't worry
Use my code below , It will definetely solve your problem,
#Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
LayoutInflater inflator = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View row = inflator.inflate(R.layout.single_row, null, false);
ImageView myImage = (ImageView) row.findViewById(R.id.imageView1);
TextView myText = (TextView) row.findViewById(R.id.textView1);
TextView mydesc = (TextView) row.findViewById(R.id.textView2);
myImage.setImageResource(images[position]);
myText.setText(mytitle[position]);
mydesc.setText(mydescp[position]);
return row;
}
If still problem persists then post logcat exception stack trace ,I will help you
There is a another approach , You just have to import android.view.LayoutInflater; and take the context of parent (ViewGroup) - parent.getContext() ,It will work
#Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
View v = LayoutInflater.from(parent.getContext()).inflate(
R.layout.single_row, parent, false);
You have to use this code
View row = convertView;
before this line,
View row = inflator.inflate(R.layout.single_row, parent, false);
Hope it works..
Related
I'm working with a custom ListView with custom Adapter which only has EditText and TextView in each row, the problem is in scroll, when there is something in the first row, for example, it doesn't matter how long is the text in the field, if it goes out of the screen while scrolling, then if I get back to it, it looses the text it had
#Override
public View getView(int i, View view, ViewGroup viewGroup) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View itemView = inflater.inflate(R.layout.campos, viewGroup, false);
TextView tv= itemView.findViewById(R.id.lblNumeroCampo);
EditText txtCampo = itemView.findViewById(R.id.txtCampo);
txtCampo.setText(elementos.get(i));
tvNumero.setText("" + (i +1));
return itemView;
}
I just want not to lose text that is in any field of the list, thanks to those who want to help me.
I think you don't need to call the findViewById every time the getview action fired.
You can also use a holder class.
Your UI classes should be called once when the view class is null.
The view class can save the holder class with setTag method then reuse them by getTag.
Here is my suggestion.
class ViewHolder
{
TextView tvNumero;
EditText txtCampo;
}
public View getView(int position, View view, ViewGroup viewGroup) {
ViewHolder holder;
if(view == null)
{
view = inflater.inflate(resource, viewGroup, false);
holder = new ViewHolder();
holder.tvNumero= view.findViewById(R.id.lblNumeroCampo);
holder.txtCampo = view.findViewById(R.id.txtCampo);
view.setTag(holder);
} else {
holder = (ViewHolder) view.getTag();
}
holder.txtCampo.setText(elementos.get(i));
holder.tvNumero.setText("" + (i +1));
return view;
}
Have a good coding.
This happens because android calls getView() everytime the view goes out of visible space and appears again. Since you are creating a new view in your getView() method, there is no recycling happening. Everytime the getView() method is called, a new view is returned with no text in it.
As mentioned by #tommybee, you can use a view holder class that checks to see if the view has already been initialized and return the initialized view if called.
Alternatively, I would suggest you to use RecyclerView instead of ListView, which makes using ViewHolder pattern mandatory. Reason is explained clearly here
I know recycle view is new but I want to know what is difference in 2 codes in list view. I have already tried to search a lot but not get specific answer. I know First one is more faster then the second because of memory consumption but why second code is slow then the first one what is the internal process can any one enplane it.
This is the first Code
#Override
public View getView(final int position, View convertView, ViewGroup parent) {
final HashMap<String ,String > item = lst.get(position);
ViewHolderItem viewHolder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.shadow_request_row, parent, false);
viewHolder = new ViewHolderItem();
viewHolder.title = (TextView)convertView.findViewById(R.id.item_name);
viewHolder.msg = (TextView)convertView.findViewById(R.id.message);
convertView.setTag(viewHolder);
}else{
viewHolder = (ViewHolderItem) convertView.getTag();
}
viewHolder.title.setText(item.get(Const.USERNAME));
viewHolder.msg.setText(item.get(Const.GET_MESSAGE));
return convertView;
}
This is the Second Code
#Override
public View getView(final int position, View convertView, ViewGroup parent) {
final HashMap<String ,String > item = lst.get(position);
ViewHolderItem viewHolder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.shadow_request_row, parent, false);
viewHolder = new ViewHolderItem();
viewHolder.title = (TextView)convertView.findViewById(R.id.item_name);
viewHolder.msg = (TextView)convertView.findViewById(R.id.message);
}
viewHolder.title.setText(item.get(Const.USERNAME));
viewHolder.msg.setText(item.get(Const.GET_MESSAGE));
return convertView;
}
The second example is missing the part about saving the viewHolder as the tag of the created view if the view is just being inflated and reusing the viewHolder if the view already exists.
List View items are re created whenever it wants. (This happens when you scroll up and down). Whenever a ListView needs to re create an item it calls the getView() of the adapter with the required position. Inside the getView() method you have the logic to generate the item View required for that position.
The method findViewById() that you use to find a View inside the XML, is CPU extensive. You might see a considerable lag if your XML contains a long sequence of children and the getView() contains lots of findViewById() calls.
This is where a ViewHolder comes handy. A ViewHolder is a class that can hold the View items. You can use the already created ViewHolder objects instead of calling findViewById() every time.
To make use of this you have to save a ViewHolder object associated with a particular position. You do it like this.
ViewHolder viewHolder;
if(convertView==null){
//the view is created for the first time
//you have to make the View HOlder object here
viewHOlder=new ViewHOlder(convertView);
//ViewHOlder constructor can find the required view elements and store it in variables
//now you have to save this View Holder object for future reference
//you save it as a tag
convertView.setTag(viewHolder);
}
Now you have a defined View Holder for the specific item position. Here is how to re use it.
When the ListView adapter wnats to re use it the convertView given to getItem() is not null. So the re use occurs in the else statement of the above if.
else{
//you already have a pre created View holder. Retrieve it.
viewHOlder=(ViewHolder)convertView.getTag();
//now you can get access to your View elements easily
}
In you second example, you create the ViewHOlder but you never re use it. So it makes not improvement.
I am trying to create a listview with each list item is different and their layouts are created by code. The initial layouts look fine, but when i scroll out and in, all the layout items added programatically are added again, resulting duplicate items. How can I solve that problem?
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;
MyHolder holder;
if (v == null) {
LayoutInflater li = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = li.inflate(R.layout.empty_item, null);
holder = new MyHolder(v);
v.setTag(holder);
} else {
holder = (MyHolder) v.getTag();
}
TextView textView = new TextView(activity);
textView.setText(items.get(position).getItems().get(i).getText());
textView.setLayoutParams(params);
holder.linearLayout.addView(textView);
return v;
}
class MyHolder{
public TextView tvTitle;
public LinearLayout linearLayout;
public CardView cardView;
public MyHolder(View base){
tvTitle = (TextView)base.findViewById(R.id.tvTitle);
cardView = (CardView)base.findViewById(R.id.card_view2);
linearLayout = (LinearLayout)base.findViewById(R.id.linearLayoutCard);
}
}
I'm not even sure how this code is running, because you have no return statement in your getView() method. But you need to return the convertView in getView() so that the ListView can reuse those when it needs to. Otherwise, it'll just keep asking for new views every time it needs them. So you would just put return v; at the end of getView().
Additionally, you are creating and adding new TextViews to your MyHolder objects outside of the if (v == null) block. Normally you would instantiate new views like this if the convertView is null. If it isn't, you just pass it through to the ListView or make updates to it before passing it back. So what's happening is, the convertView is available (not null), but instead of using it, you're adding a brand new TextView instead, which is why you are getting duplicates.
I am having an unclear issue concerning the recycling of views in a getView method of a custom array adapter.
I understand that elements are reused, but how do I know exact what to implement in the first part of the if statement, and what in the second?
Right now I am having following code. I came to this question due to dropping the code in the second part of the statement which results in a list of the first 9 elements, which are repeated numberous times instead of all elements. I didn't really know what is causing this exactly...
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View row = convertView;
if (row == null) {
LayoutInflater inflater = ((Activity) context).getLayoutInflater();
row = inflater.inflate(layoutResourceId, parent, false);
title = getItem(position).getTitle();
size = calculateFileSize(position);
txtTitle = (TextView) row.findViewById(R.id.txtTitle);
tvFileSize = (TextView) row.findViewById(R.id.tvFileSize);
txtTitle.setText(title);
tvFileSize.setText(size);
} else {
title = getItem(position).getTitle();
size = calculateFileSize(position);
txtTitle = (TextView) row.findViewById(R.id.txtTitle);
tvFileSize = (TextView) row.findViewById(R.id.tvFileSize);
txtTitle.setText(title);
tvFileSize.setText(size);
}
return row;
}
It's easy. The first time no row is created, so you have to inflate them. Afterwards, the Android os may decide to recycle the views that you already inflated and that are not visible anymore. Those are already inflated and passed into the convertView parameter, so all you have to do is to arrange it to show the new current item, for example placing the right values into the various text fields.
In short, in the first part you should perform the inflation AND fill the values, in the second if (if convertView != null) you should only overwrite the field because, given the view has been recycled, the textviews contain the values of the old item.
This post and this are good starting points
I understand that elements are reused, but how do I know exact what to implement in the first part of the if statement, and what in the second?
The organization is quite simple once you get the hang of it:
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
/* This is where you initialize new rows, by:
* - Inflating the layout,
* - Instantiating the ViewHolder,
* - And defining any characteristics that are consistent for every row */
} else {
/* Fetch data already in the row layout,
* primarily you only use this to get a copy of the ViewHolder */
}
/* Set the data that changes in each row, like `title` and `size`
* This is where you give rows there unique values. */
return convertView;
}
For detailed explanations of how ListView's RecycleBin works and why ViewHolders are important watch Turbo Charge your UI, a Google I/O presentation by Android's lead ListView programmers.
You want to create a ViewHolder class in your MainActivity. Something like
static class ViewHolder
{
TextView tv1;
TextView tv2;
}
then in your getView, the first time you get your Views from your xml in the if and reuse them after that in the else
View rowView = convertView;
if (rowView == null)
{
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
rowView = inflater.inflate(R.layout.layout_name_to_inflate, parent, false);
holder = new ViewHolder();
holder.tv1= (TextView) rowView.findViewById(R.id.textView1);
holder.tv2 = (RadioGroup) rowView.findViewById(R.id.textView2);
rowView.setTag(holder);
}
else
{
holder = (ViewHolder) rowView.getTag();
}
I would recommend that you use the View holder and convertview pattern to create your listView as it will be more efficient.Here is a good explanation of how it works with a re-use strategy. This will answer your question on how re-cycling works. If you want to refer to a code sample, I have it on GitHub.
Hope this helps.
The last part of the question I really couldn't grasp without a picture of the effect but for the first part "what to implement in the first part of the if statement, and what in the second" I think I've found the this implementation very common.
You would find the view references first and store them to a static class ViewHolder which then you attach to the tag of the new inflated view. As the listview recycles the views and a convertView is passed getView you get the ViewHolder from the convertView's tag so you don't have to find the references again (which greatly improves performance) and update the view data with that of your object at the position given.
Technically you don't care what position the view was since all you care for is the references to the views you need to update which are held within it's ViewHolder.
#Override
public View getView(int position, View convertView, ViewGroup container) {
ViewHolder holder;
Store store = getItem(position);
if (convertView == null) {
convertView = mLayoutInflater.inflate(R.layout.item_store, null);
// create a holder to store references
holder = new ViewHolder();
// find references and store in holder
ViewGroup logoPhoneLayout = (ViewGroup) convertView
.findViewById(R.id.logophonelayout);
ViewGroup addressLayout = (ViewGroup) convertView
.findViewById(R.id.addresslayout);
holder.image = (ImageView) logoPhoneLayout
.findViewById(R.id.image1);
holder.phone = (TextView) logoPhoneLayout
.findViewById(R.id.textview1);
holder.address = (TextView) addressLayout
.findViewById(R.id.textview1);
// store holder in views tag
convertView.setTag(holder);
} else {
// Retrieve holder from view
holder = (ViewHolder) convertView.getTag();
}
// fill in view with our store (at this position)
holder.phone.setText(store.phone);
holder.address.setText(store.getFullAddress());
UrlImageViewHelper.setUrlDrawable(holder.image, store.storeLogoURL,
R.drawable.no_image);
return convertView;
}
private static class ViewHolder {
ImageView image;
TextView phone;
TextView address;
}
i have a ListView with a onClicklListener.
The ListView has a row Layout of say /res/listitem_a
now after an onClickevent of the any listitem , i want to change the layout of
only that listitem to say /res/listitem_b..
any help on how shall i proceed.
Use BaseAdapter and modify in getView call.
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.custom_layout, 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);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
// Change text size
holder.text.setTextAppearance(context,R.style.customStyle);
return convertView;
}
static class ViewHolder {
TextView text;
}
And you can use position variable in getView call to change specific row. Hope this help!!!
You can use ViewFlipper as layout of the rows. With ViewFlipper you can specify as many layouts as you want and flip among them when something happen (like a click event). Here is a good tutorial about ViewFlipper.
Moreover, you should implement a custom adapter, extending BaseAdapter, and overriding the getView method.
#Override
public View getView(int position, View view, ViewGroup parent) {
if (view == null) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view = inflater.inflate(R.layout.your_row_layout, null); //this will inflate the layout into each row
}
//from here on, assign the information to display to the layout widgets
Hope I've helped you.