java - ListView 条目在滚动时会更改其布局

Question

嗨，我发现了一个非常奇怪的问题，我无法理解..希望有人可以帮助我:

如果所有 View 都显示在屏幕上，我的列表看起来会很棒。一旦屏幕变小(或列表变长)，有时条目的 View 就会与应有的不同。可以通过向上或向下滚动以使条目移出窗口来限制此问题。

我有一个 ListView ，其中包含不同的条目类型，并且具有不同的布局文件。这是应该决定显示什么布局的方法:

public View getView(int position, View view, ViewGroup parent) {
        NavigationListEntry i = entries.get(position);
        View v = view;
        if (v == null)
            switch(i.Type) {
            case ACTIVE_ENTRY:
                v = inflater.inflate(R.layout.list_nav_row_active, null);
                break;
            case HEADER:
                v = inflater.inflate(R.layout.list_nav_row_header, null);
                break;
            ...
            default:
                v = inflater.inflate(R.layout.list_nav_row_active, null);
                break;
            }
}

您知道为什么会发生这种情况吗？

/编辑如果我只是删除“if (v == null)”，它似乎可以工作

Answer 1

如果删除if(v==null)，您就不会重用已经膨胀的 View 。如果这样做， ListView 将会有点迟缓。

最好的办法是

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder = null;
    NavigationListEntry i = getItem(position);
    if(null == convertView){
        convertView = inflateNewView(i.type);
        holder = (ViewHolder) convertView.getTag();
    } else{
        //getting tag to obtain the already found views
        holder = (ViewHolder) convertView.getTag();
        if(holder.type != i.type){
            convertView = inflateNewView(i.type); 
            holder = (ViewHolder) convertView.getTag();
        }
    }

    //always update the elements 
    holder.title.setText(i.getTitle());
    holder.desc.setText(i.getDesc());
    holder.content.setText(i.getContent());

    return convertView;
}

/**
 * Inflates a new view for the specified type
 * @return the newly inflated view
 */
private View inflateNewView(int type){
        View convertView = null;
        switch(type) {
        case ACTIVE_ENTRY:
            convertView = inflater.inflate(R.layout.list_nav_row_active, null);
            break;
        case HEADER:
            convertView = inflater.inflate(R.layout.list_nav_row_header, null);
            break;
        ...
        default:
            convertView = inflater.inflate(R.layout.list_nav_row_active, null);
            break;
        }
        holder = new ViewHolder();
        convertView = inflater.inflate(LAYOUT_RESOURCE, null);
        holder.title = (TextView) convertView.findViewById(R.id.txtTitle);
        holder.desc = (TextView) convertView.findViewById(R.id.txtDesc);
        holder.content = (TextView) convertView.findViewById(R.id.txtContent);
        holder.type = type;
        //setting tag to reduce hierarchy lookup
        convertView.setTag(holder);

    return convertView;
}
/**
 * Holder class to improve performance. Helps in reducing view hierarchy lookup
 */
private static class ViewHolder {

    TextView title;
    TextView desc;
    TextView content;
    int type;

}   

这是最好的方法，至少会尝试回收您的 View 。希望这有帮助