I've written this code from a tutorial.
#Override
public View getView(int i, View view, ViewGroup viewGroup) {
// TODO Auto-generated method stub
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View row = inflater.inflate(R.layout.single_row, viewGroup,false);
TextView title = (TextView) row.findViewById(R.id.txtTitle);
TextView description = (TextView) row.findViewById(R.id.txtDescription);
ImageView image = (ImageView) row.findViewById(R.id.imgPic);
SingleRow temp = list.get(i);
title.setText(temp.title);
description.setText(temp.description);
image.setImageResource(temp.image);
return row;
}
In this line of code:
TextView title = (TextView) row.findViewById(R.id.txtTitle);
I think a TextView is copied to a variable of the same kind. and then in this line of code:
title.setText(temp.title);
we fill that variable with something. then the row variable which is a View and it's not related to 'title' variable is returned.
How it works? I thinks these variables have nothing to do here.
This code inflates a new view, settings it's contents. This means that you're creating a new view programatically. It's often used i.e. when populating a list, where you'll have number of rows, each identical in structure, but with different values.
Here is how it works:
#Override
public View getView(int i, View view, ViewGroup viewGroup) {
// Get the inflater service
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
// Inflate view with ID = R.layout.single_row into the row variable
View row = inflater.inflate(R.layout.single_row, viewGroup,false);
// Get child views of row: title, description and image.
TextView title = (TextView) row.findViewById(R.id.txtTitle);
TextView description = (TextView) row.findViewById(R.id.txtDescription);
ImageView image = (ImageView) row.findViewById(R.id.imgPic);
// This get's some template view which will provide data: title, description and image
SingleRow temp = list.get(i);
// Here you're setting title, description and image by using values from `temp`.
title.setText(temp.title);
description.setText(temp.description);
image.setImageResource(temp.image);
// Return the view with all values set. This view will be later probably added somewhere as a child (maybe into a list?)
return row;
}
That's the method used to return the view for a row in the listview. row variable is actually related to title, as you can see here.-
TextView title = (TextView) row.findViewById(R.id.txtTitle);
in other words, title is a TextView inside row object, and that code retrieves it to set its text. To sum up, the whole getView method is inflating a single_row View, and setting properties for all relevant children of row.
View row = inflater.inflate(R.layout.single_row, viewGroup,false);
You are inflating a layout single_row
TextView title = (TextView) row.findViewById(R.id.txtTitle);
Initializing textview which is in singlerow.xml
title.setText(temp.title);
Setting title to textview.
You are infalting a layout for each row in listview.
Also it is better to use a viewHolder pattern.
http://developer.android.com/training/improving-layouts/smooth-scrolling.html
Also you can move the below to the constructor of adapter class and declare inflater as a class member
inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
The below link may be of interest to you
How ListView's recycling mechanism works
Related
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..
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;
}
My listview contains one image,and some textview; there are two textiview which contains the price and special price,if special price is 0 than set only price textview and special price let it null,but special price is > 0 than set price value as well special price,fisrt time everything is going good but when i am scrolling the listview then blank textview set with dumyy valueenter code here
Here is my getView method code.
#Override
public View getView(final int position, View convertView, ViewGroup parent){
//public View getView(int position, View convertView, ViewGroup parent) {
/*View vi = convertView;
if (convertView == null)
{
vi = inflater.inflate(R.layout.list_row, null);
}
*/
int pos=position;
if (convertView == null) {
convertView = inflater.inflate(R.layout.list_row, null);
viewHolder=new ViewHolder();
viewHolder.txt_id = (TextView) convertView.findViewById(R.id.id); // title
viewHolder.txt_product_name = (TextView) convertView.findViewById(R.id.title); // title
viewHolder.artist = (TextView) convertView.findViewById(R.id.artist); // artist
// name
viewHolder.txt_mspecialprice_withouttax = (TextView) convertView.findViewById(R.id.duration); // duration
viewHolder.stock = (TextView) convertView.findViewById(R.id.stck);
viewHolder.txt_mprice_withouttax = (TextView) convertView.findViewById(R.id.txtmpricewithouttax);
viewHolder.thumb_image = (ImageView) convertView.findViewById(R.id.list_image); // thumb
// image
convertView.setTag(viewHolder);
}
else{
viewHolder = (ViewHolder) convertView.getTag();
}
HashMap<String, String> song = new HashMap<String, String>();
song = data.get(position);
// Setting all values in listview
String mspecialprice_str=song.get(CustomizedListView.KEY_PRODUCT_MSPECIAL_WITHOUT_TAX);
//String substr_mspecialprice_str=mspecialprice_str.substring(1,mspecialprice_str.indexOf("."));
//String substr_mspecialprice_str_replaced=substr_mspecialprice_str.replace(",", "");
String msaleprice_str=song.get(CustomizedListView.KEY_PRODUCT_MPRICE_WITHOUT_TAX);
//String substr_msaleprice_str=msaleprice_str.substring(0,msaleprice_str.indexOf("."));
//String substr_msaleprice_str_replaced=substr_msaleprice_str.replace(",", "");
viewHolder.txt_id.setText(song.get(CustomizedListView.KEY_PRODUCT_ID));
viewHolder.txt_product_name.setText(song.get(CustomizedListView.KEY_PRODUCT_NAME));
viewHolder.artist.setText(song.get(CustomizedListView.KEY_PRODUCT_DESCRIPTION));
viewHolder.stock.setText(song.get(CustomizedListView.KEY_STOCK));
if(mspecialprice_str.equals("0"))
{
//txt_mspecialprice_withouttax.setText(song.get(CustomizedListView.KEY_PRODUCT_MSPECIAL_WITHOUT_TAX));
viewHolder.txt_mprice_withouttax.setText("$"+(song.get(CustomizedListView.KEY_PRODUCT_MPRICE_WITHOUT_TAX)));
viewHolder.txt_mprice_withouttax.setTextColor(Color.parseColor("#64aef9"));
}
//if(!(mspecialprice_str.equals("0")))
//{
else
{
viewHolder.txt_mspecialprice_withouttax.setText("$"+(song.get(CustomizedListView.KEY_PRODUCT_MSPECIAL_WITHOUT_TAX)));
viewHolder.txt_mprice_withouttax.setText("$"+(song.get(CustomizedListView.KEY_PRODUCT_MPRICE_WITHOUT_TAX)));
viewHolder.txt_mprice_withouttax.setPaintFlags(viewHolder.txt_mprice_withouttax.getPaintFlags() | Paint.STRIKE_THRU_TEXT_FLAG);
viewHolder.txt_mprice_withouttax.setTextColor(Color.parseColor("#F01616"));
}
imageLoader.DisplayImage(
song.get(CustomizedListView.KEY_PRODUCT_IMAGEURL), viewHolder.thumb_image);
return convertView;
}
}
class ViewHolder {
TextView txt_id ; // title
TextView txt_product_name; // title
TextView artist ; // artist
// name
TextView txt_mspecialprice_withouttax; // duration
TextView stock ;
TextView txt_mprice_withouttax;
ImageView thumb_image ; // thumb
}
ListView, GridView reuse views used as list items/grid elements. getView() is called everytime android tries to draw next element while scrolling your view. There is no need to prevent that!
Edit - Atrix1987
From the developer docs
An Adapter object acts as a bridge between an AdapterView and the underlying data for that view. The Adapter provides access to the data items. The Adapter is also responsible for making a View for each item in the data set.
Suppose you have 10 elements which you want to show using your GridView/ListView and the maximum visible items is 5 then the same 5 views can be reused to display the rest of the 5 elements when you scroll. This is the intended behavior and is the right way to do things [keeps number of views to a minimum].
You don't have control on getView method, the framework does that for you.
The GridView widget extends AdapterView. It uses the adapter to allow the reuse of Views and improve performance. There is no way to avoid calling getView() - it is essential to the whole AdapterView idea. If you want a static layout, perhaps you should use something else.
I created the Layout design using java code only not from the XML Layout Designs. The code I used is following
public View getView(int position, View convertView, ViewGroup parent) {
TextView tv = new TextView(mContext);
tv.setText(hotelList.get(position).name);
return tv;
}
How to use layoutInflator for creating layout fro this. I need 2 more textviews in a single list item. the whole list contains 10 different list items
Please provide some codes for this. Help appreciated
I have gone through this before by having my static class too. Check this out, it will help:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View rowView = convertView;
if ( rowView == null) {
LayoutInflater inflator = this._activity.getLayoutInflater();
rowView = inflator.inflate(R.layout.todolistlisting, null);
TodoListViewHolder viewHolder = new TodoListViewHolder();
viewHolder._name = (TextView) rowView.findViewById(R.id.tVTLName);
viewHolder._completed = (TextView) rowView.findViewById(R.id.tVTLCCount);
viewHolder._remaining = (TextView) rowView.findViewById(R.id.tVTLRCount);
rowView.setTag(viewHolder);
}
TodoListViewHolder holder = (TodoListViewHolder) rowView.getTag();
VO_TodoList votodolist = this._items.get(position);
holder._name.setText(votodolist._title);
holder._completed.setText(votodolist._completed);
holder._remaining.setText(votodolist._remaining);
return rowView;
}
TodoListViewHolder is my view component holder here. like your TextView.
I guess you know how to make XML layout for this layout. So just make the XML layout and get the object of the main layout using the following code:
LinearLayout mainLayout=(LinearLayout) View.inflate(R.layout.yourlayout); //if yourlayout.xml is the name of the xml file you made and put in the layout folder.
To get the child of the layout, let's say if it's a TextView with the id text, then the code would be:
TextView textView=(TextView)mainLayout.findViewById(R.id.text);
You can add view at runtime by using inflater like this
LinerLayout linearLayout = (LinearLayout)inflater.inflate(R.layout.news_categories_item, null);
TextView categoryValueTextView = (TextView)linearLayout.findViewById(R.id.news_category_item_value);
mMainLinearLayout.addView(categoryValueTextView);
Here i am inflating one text view which is there in another linear layout(this is simple linear layout which holds only textview) at runtime and adding it to my main linear layout.
you can get the inflater object in your acitivity by using getLayoutInflater(). And if you want to get inflater in adapter you have to pass inflater object to constructor of adapter from your activity.
Good time!
My Android app has so feature that I use ListView in the one of the page of TabHost without layout for ListView. Like that:
ListView lv = new ListView(this);
lv.setAdapter(myAdapter);
So I'd like to change some row's properties like text size in the row. So, how can I get access to the properties of the explicit row of ListView to change text size, for example?
Use BaseAdapter and modify font size 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!!!