János János - 3 months ago 19
Android Question

How to force GridView to load cells

GridView
is scrolled programmatically, and no new item appears coming up from the bottom.

I tried to update with the following line, but it does not force
GridView
to load new items.

imageAdapter.notifyDataSetChanged();
gridview.invalidateViews();
gridview.setAdapter(imageAdapter);


enter image description here




Simplified the app, now the scrolling can be fired with button click, but the upcoming empty items are still appearing. Here is some code:

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

final CustomGridView gridview = (CustomGridView) findViewById(R.id.gridView1);
final ImageAdapter imageAdapter = new ImageAdapter(this);
gridview.setAdapter(imageAdapter);

gridview.setNumColumns(3);
LinearLayout.LayoutParams linearParams = (LinearLayout.LayoutParams)gridview.getLayoutParams();
linearParams.width=66*3;
gridview.setLayoutParams(linearParams);


final Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {

gridview.scrollBy(0, 44);
}
});
}





public class ImageAdapter extends BaseAdapter {
private Context mContext;

public ImageAdapter(Context c) {
mContext = c;
}

public int getCount() {

return 300;
}

public Object getItem(int position) {
return null;
}

public long getItemId(int position) {
return 0;
}

// create a new ImageView for each item referenced by the Adapter
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView;
if (convertView == null) {
// if it's not recycled, initialize some attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(66, 66));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(0, 0, 0, 0); // 8 8 8 8
} else {
imageView = (ImageView) convertView;
}

imageView.setImageResource(R.drawable.asdf);
return imageView;
}
}





<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.j4nos.moviebuffs12.MainActivity">

<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New Button"
android:id="@+id/button"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />

<HorizontalScrollView
android:id="@+id/horizontalScrollView"
android:layout_width="198dp"
android:layout_height="match_parent"
android:layout_marginTop="66dp"
android:layout_marginLeft="0dp"
android:layout_marginBottom="0dp">

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">

<com.j4nos.moviebuffs12.CustomGridView
android:id="@+id/gridView1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="0dp"
android:columnWidth="66dp"

android:horizontalSpacing="0dp"
android:scrollbarAlwaysDrawHorizontalTrack="true"
android:scrollbarAlwaysDrawVerticalTrack="true"
android:scrollbars="horizontal"
android:stretchMode="none"
android:verticalSpacing="0dp"
android:listSelector="@null"
android:scaleType="centerCrop">

</com.j4nos.moviebuffs12.CustomGridView>

</LinearLayout>

</HorizontalScrollView>

</RelativeLayout>





public class CustomGridView extends GridView {

public CustomGridView(Context context) {
super(context);
}

public CustomGridView(Context context, AttributeSet attrs) {
super(context, attrs);
}

public CustomGridView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}

/* ADD THIS */
@Override
public int computeVerticalScrollOffset() {
return super.computeVerticalScrollOffset();
}
}

Answer

I think the problem is with the way you are scrolling:

gridview.scrollBy(0, 44);

This moves the gridview, not the content of the gridview. You can verify this by adding the following into your layout inside the CustomGridView component:

android:fastScrollAlwaysVisible="true"

Now you can see it's not the gridview content that is being interacted with on the button press.

Instead, I suggest you try to use:

gridview.scrollListBy(44);

if your API level allows it.