I have created a ListView and its custom Adapter. But due to some reason I am not allowed to get items from ViewHolder.
In my case ViewHolder has only one variable and that is of LinearLayout. LinearLayout contains the other child views(which is decided and created at run time). When I use ViewHolder and set the tag of holder object, on scroll I am getting the same views again.
Is there any other way to stop adapter to create views while scrolling ?
Or, while scrolling how can we clear the references of views ?
I have find this but I don't think this will work.
setRecyclerListener(new RecyclerListener() {
#Override
public void onMovedToScrapHeap(View view) {
//from here can we use this to clean the memory
}
});
ViewHolder is meant as a holder to contain ids of listitem layout.
It is optimization to avoid calling findViewById everytime new listitem is created for display by going through data container e.g. arrayList.
You cannot stop adapter in between creating item views.
Only items on display are created.
convertView acts as object being recycled for creating subsequent view while scrolling up/down.
You will not be able to use view holder for the purpose you are trying to achieve.
Sample usage as below.
#Override
public View getView(int position, View convertView, ViewGroup parent)
{
View v = convertView;
ViewHolder viewHolder = null;
if(convertView == null)
{
v = LayoutInflater.from(StockDetailsActivity.this).inflate(R.layout.stock_details_list_item, null);
viewHolder = new ViewHolder();
viewHolder.model_name_tv = (TextView) v.findViewById(R.id.model_name);
viewHolder.model_type_iv = (ImageView) v.findViewById(R.id.model_type_icon);
viewHolder.model_type_tv = (TextView) v.findViewById(R.id.model_type_desc);
viewHolder.model_stock_tv = (TextView) v.findViewById(R.id.model_stock_value);
v.setTag(viewHolder);
}
else
viewHolder = (ViewHolder) v.getTag();
stockCursor.moveToPosition(position);
// logic to update data to views as appropriate goes here
return v;
}
public class ViewHolder{
public TextView model_name_tv;
public ImageView model_type_iv;
public TextView model_type_tv;
public TextView model_stock_tv;
}
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 defined a Adapter which extends BaseAdapter when I use ListView to display something.I overrided View getView (int position, View convertView, ViewGroup parent) method to reuse View component, in the method, I also wrote if(convertView == null) {System.out.println("test");} block. There are 50 rows data in ListView and the screen only can display about 20 rows data. when I ran the application, LogCat printed less than 50 rows of "test" though I slided the screen to make sure all data are loaded.But why ? I think it should print 50 rows data. Here is the key code:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null) {
convertView = inflater.inflate(resource, null);
System.out.println(++count + "convertView == null:" + convertView);
}
}
someone help me please, I am a newbie.... thanks
Android does not inflate a View for every item in your adapter. It reuses inflated views previously used for other items.
The pattern for binding views in a adapter is something like this:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View view;
if(convertView == null) {
view = inflater.inflate(resource, null);
} else {
view = convertView;
}
// bind data to view here
return view;
}
In fact you normally would use a ViewHolder class. But first fix your basic adapter before reading about that.
Because convertView will be null only if there isn't a previously returned view that can be recycled (i.e. it's no longer on screen).
The views you return from an adapter's getView() can be recycled in later calls to getView(). The framework passes such recyclable views in via the convertView arg.
So your convertView == null branch only gets run enough times to fill the listview screen once and after that, when scrolling, these old views get recycled.
You missing return view.
ListView recycles view. How ListView's recycling mechanism works
Use a ViewHolder pattern
http://developer.android.com/training/improving-layouts/smooth-scrolling.html
#Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if(convertView == null) {
convertView = inflater.inflate(resource, null);
holder = new ViewHolder();
holder.tv = (TextView)convertView.findViewById(R.id.textView1);
//initialize views
convertView.setTag(holder);
} else {
holder =(ViewHolder) convertView.getTag();
}
// update your view here
holder.tv.setText("hi");
return convertView;
}
static class ViewHolder {
// YourViews Declaration
TextView tv; // an example
}
http://developer.android.com/design/media/lists_main.png
As you can see above, I would like to create the 3-line list.
I have looked everywhere but I can't seem to find any documentation on how to do it.
How do I write my adapter for this kind of ListView?
Do I have to extend ListActivity, include a ListView in my .xml layout, or both?
Can somebody provide further insight into it? I'll be very grateful...
You create an XML-Layout for your list-item (row) with three TextViews in a vertical LinearLayout. Then you need to subclass the ArrayAdapter to fill the TextViews. In the getView you fill the lines.
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;
if (convertView == null) {
LayoutInflater vi = (LayoutInflater) mContext
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = vi.inflate(R.layout.listitem, null);
}
TextView text1 = (TextView) convertView.findViewById(R.id.textfield1);
if (text1 != null) {
text1.setText(contentArray.get(position).valueForField1);
}
// same for the other fields
return v;
}
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!!!