[英]In Android, how to achieve snap effect on a listview while respecting acceleration caused by fling?
為了演示,我有一個ListView顯示一個數字列表。 我想達到這樣的效果:當用戶滾動ListView並結束滾動時,它只會停止在某些位置,這樣第一個可見項始終會完整顯示。 我在下面附加了我的嘗試代碼。 當用戶拖動以滾動ListView時,它可以工作。 但是,在猛沖時,正常的加速度會中斷,從而導致不自然的停止。 我的問題是,在達到相同效果的同時,如何考慮由猛擊引起的加速度?
package com.example.snaptest;
import android.content.Context;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
private static class TestListViewAdapter extends BaseAdapter {
private Context mContext;
public TestListViewAdapter(Context context) {
mContext = context;
}
@Override
public int getCount() {
return 100;
}
@Override
public Object getItem(int position) {
return Integer.toString(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
TextView textView = new TextView(mContext);
textView.setText(Integer.toString(position));
AbsListView.LayoutParams params = new AbsListView.LayoutParams(ViewGroup.LayoutParams
.MATCH_PARENT, 180);
textView.setLayoutParams(params);
return textView;
}
}
private static class TestListView extends ListView {
public TestListView(Context context) {
super(context);
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_UP || ev.getAction() == MotionEvent.ACTION_CANCEL) {
View itemView = getChildAt(0);
int top = Math.abs(itemView.getTop()); // top is a negative value
int bottom = Math.abs(itemView.getBottom());
if (top >= bottom){
smoothScrollToPositionFromTop
(getFirstVisiblePosition() + 1, 0);
} else {
smoothScrollToPositionFromTop
(getFirstVisiblePosition(), 0);
}
}
return super.onTouchEvent(ev);
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TestListView listView = new TestListView(this);
listView.setAdapter(new TestListViewAdapter(this));
setContentView(listView);
}
}
我會嘗試使用OnScrollListener
而不是擴展ListView
。
像這樣:
listView.setOnScrollListener(new AbsListView.OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (scrollState == AbsListView.SCROLL_STATE_IDLE) {
// snap the listview according to the top/bottom items' visibility
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
}
});
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