Question

我有一个ListView。在适配器内部，当我执行以下操作（下面的代码）时，firstVisible仅在列表首次显示时等于position。在滚动期间，当视图明显位于顶部时，适配器仍然没有将其捕获为位于顶部。

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    ...
        int firstVisible = ((ListView) parent).getFirstVisiblePosition();
            if (firstVisible == position) {/
                //print some stuff and do work
            } else {
                //print some other stuff and do other work
            }
        }
        return rowView;
    }

所以我的问题是，在滚动过程中如何跟踪特定项目何时位于ListView的顶部？我想从适配器中做到这一点。

修改

当有问题的视图到达顶部时：首先我要将其设置为GONE，以使其不可见。事实上，如果我只能这样做，那就太好了。然后我想抓住它的数据进行一些工作。

Answer 1

好吧我想我有一个解决方案：

public class MyActivity extends Activity {

    ListView             listView;
    ArrayAdapter<String> adapter;
    int firstVisible;

    /** Called when the activity is first created. */
    @Override

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        listView = (ListView) findViewById(R.id.listView);

        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1) {
            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                View v = super.getView(position, convertView, parent);
                processView(v, getItem(position), true);
                return v;
            }
        };

        for (int i = 0; i < 30; i++) {
            adapter.add("Value " + String.valueOf(i + 1));
        }

        listView.setAdapter(adapter);
        firstVisible = listView.getFirstVisiblePosition();
        listView.setOnScrollListener(new AbsListView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(AbsListView view, int scrollState) {

            }

            @Override
            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                if (firstVisibleItem != firstVisible) {
                    onFirstVisibleChanged(firstVisible, firstVisibleItem);
                    firstVisible = firstVisibleItem;
                }
            }
        });
    }

    private void processView(View v, String value, boolean fromGetView) {
        //if from get view we don't want to set yet wait till it comes from scrolling
        if (value.contains("4") && !fromGetView) {
            v.setBackgroundResource(android.R.color.holo_orange_light);
        } else {
            v.setBackgroundResource(android.R.color.transparent);
        }
    }

    private void onFirstVisibleChanged(int oldIndex, int newIndex) {
        View v = getViewForPosition(newIndex);
        String val = adapter.getItem(newIndex);
        processView(v, val, false);
    }

    /**
     * @param position
     *            position of item in list
     * @return null if position outside bounds
     */
    public View getViewForPosition(int position) {
        int firstPosition = listView.getFirstVisiblePosition() - listView.getHeaderViewsCount();
        int wantedChild = position - firstPosition;
        // Say, first visible position is 8, you want position 10, wantedChild will now be 2
        // So that means your view is child #2 in the ViewGroup:
        if (wantedChild < 0 || wantedChild >= listView.getChildCount()) {
            return null;
        }
        return listView.getChildAt(wantedChild);
    }
}

我解释做什么的最好方法就是亲自尝试。

这样做的是将字符串“Value n”列表最多30个如果字符串在滚动时包含数字4，我们会将背景颜色更改为橙色。如果您希望删除视图，我们应该能够这样做：

private void processView(View v, String value, boolean fromGetView) {
    //if from get view we don't want to set yet wait till it comes from scrolling
    if (value.contains("4") && !fromGetView) {
        adapter.remove(value);
    } else {
        //no action needed
    }
}

然而，这可能会让用户感到非常困惑，因为值4移动到顶部时它被移除，值5移动到位。

Answer 2

在视图可见之前调用

getView，因此当您向下滚动时，大部分时间position将为firstVisible - 1，并向上滚动firstVisible + totalVisibleItems。< / p>

相反，您应该将滚动侦听器绑定到ListView

listView.setOnScrollListener(new OnScrollListener() {
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
      // Here you can change the model of the firstView and invalidate it for her to be redrawn
    }
});

在滚动期间检查项目是否在ListView适配器中的第一个位置

2 个答案: