Custom ListView Adapter `getView` Method Called Multiple Times, and No Coherent Order

android

listview-performance

viewholder-pattern

adapter-optimization

byAnton Shumikhin·Dec 3, 2024

To curb ListView performance issues, use the ViewHolder pattern to halt unnecessary view inflation and lookups. Here's an exemplary getView() method:

public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
        convertView = LayoutInflater.from(context).inflate(R.layout.item_layout, parent, false);
        holder = new ViewHolder(convertView);
        convertView.setTag(holder); // Tag! You're it!
    } else {
        holder = (ViewHolder) convertView.getTag(); // You're still it!
    }

    // Make the views hold the data
    holder.itemTitle.setText(getItem(position).getTitle());

    return convertView;
}

// A lone ranger, ViewHolder, holding the views
static class ViewHolder {
    final TextView itemTitle;

    ViewHolder(View view) {
        itemTitle = (TextView) view.findViewById(R.id.itemTitle);
    }
}

Reuse views, maintain a ViewHolder, keep getView() lean, and avoid findViewById() frequently. The direct data setting on the holder enhances user experience with smoother scrolling.

ListView Sizing: Getting It Right

For optimal ListView performance, understanding the unpredictable behavior of getView() is crucial. ListView's measurement approach can impact its execution, so avoid using wrap_content as it may lead to unnecessary layout passes.

Pin Down Your ListView Height

layout_height denoted as wrap_content in a ListView compels the system to evaluate item views multiple times. This happens when the system tries confirming the ListView's height. To ensure performing Lists, prefer using a fixed height or switch to using RecyclerView.

Listing Items Without Flinching

For the item row within ListView, layout_width and layout_height as match_parent help optimize item rendering due to a single measurement operation.

Recycling Your Views: Why & How

As getView() continuously runs in non-sequitur order during scrolling, the ListView, like a party DJ, shuffles views to save on memory.

Efficient ListView with ViewHolder

The golden rule is having a static ViewHolder. It efficiently checks getView() calls and curbs display glitches due to item repetition. ViewHolder holds onto UI parts that don't change, allowing ListView to repaint the view using new data swiftly.

ListView Size & getView() Calls

Optimizing ListView’s size can decrease excessive function calls of getView(). Incorporating conducive layout attributes for ListView with its row items indeed assures an optimal ListView execution.

ViewHolder Pattern: Inflate with Ease

Remember, view inflation is an expensive operation. The Inflator has a fixed space to work on - few getView() calls make it happier. A ViewHolder pattern contributes by reusing views and reducing getView() invocations.

Making Sense of getView() Chaos

The ListView calls getView() multiple times for a particular spot before it's displayed - its measurement process feature. We, as developers, should apprehend ListView's aim to prepare views for potential actions (swiping, scrolling) that users might take.

Harness Data Changes

ListView calls getView() on data alterations to update views. It occurs in a haphazard order as the ListView does not redraw each item linearly. Always update your adapter's data set properly to keep the ListView updates crystal clear.

Pre-Fetching: Anticipatory Measures

ListView pre-fetches views that are not immediately visible to screen to ensure smooth transitions. It might seem puzzling with multiple getView() calls, but it's a performance enhancement.

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