android listview ontouchlistener,Android ListView监听滑动事件的方法(详解)
ListView的主要有兩種滑動事件監(jiān)聽方法,OnTouchListener和OnScrollListener
1、OnTouchListener
OnTouchListener方法來自View中的監(jiān)聽事件,可以在監(jiān)聽三個Action事件發(fā)生時通過MotionEvent的getX()方法或getY()方法獲取到當(dāng)前觸摸的坐標(biāo)值,來對用戶的滑動方向進(jìn)行判斷,并可在不同的Action狀態(tài)中做出相應(yīng)的處理
mListView.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
// 觸摸按下時的操作
break;
case MotionEvent.ACTION_MOVE:
// 觸摸移動時的操作
break;
case MotionEvent.ACTION_UP:
// 觸摸抬起時的操作
break;
}
return false;
}
});
不僅僅只有上面的三種Action狀態(tài),MotionEvent類中還定義了很多其它狀態(tài),我們可以靈活的使用這些狀態(tài)
? MotionEvent.ACTION_DOWN:開始觸摸
? MotionEvent.ACTION_MOVE:觸摸移動
? MotionEvent.ACTION_UP:觸摸抬起
? MotionEvent.ACTION_OUTSIDE:觸摸范圍超過了UI邊界
? MotionEvent.ACTION_CANCEL:觸摸被取消時
? MotionEvent.ACTION_POINTER_DOWN:當(dāng)有另外一個觸摸按下時(多點(diǎn)觸摸)
? MotionEvent.ACTION_POINTER_UP:當(dāng)另一個觸摸抬起時(多點(diǎn)觸摸)
2、OnScrollListener
OnScrollListener來自AbsListView中的監(jiān)聽事件,因?yàn)長istView直接繼承自AbsListView,所以在AbsListView中有很多ListView相關(guān)信息
OnScrollListener中有兩個回調(diào)方法
? public void onScrollStateChanged(AbsListView view, int scrollState):監(jiān)聽滑動狀態(tài)的改變
? public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount):監(jiān)聽滑動
在源碼中有其詳細(xì)的解釋
/**
* Interface definition for a callback to be invoked when the list or grid
* has been scrolled.
*/
public interface OnScrollListener {
/**
* The view is not scrolling. Note navigating the list using the trackball counts as
* being in the idle state since these transitions are not animated.
*/
public static int SCROLL_STATE_IDLE = 0;
/**
* The user is scrolling using touch, and their finger is still on the screen
*/
public static int SCROLL_STATE_TOUCH_SCROLL = 1;
/**
* The user had previously been scrolling using touch and had performed a fling. The
* animation is now coasting to a stop
*/
public static int SCROLL_STATE_FLING = 2;
/**
* Callback method to be invoked while the list view or grid view is being scrolled. If the
* view is being scrolled, this method will be called before the next frame of the scroll is
* rendered. In particular, it will be called before any calls to
* {@link Adapter#getView(int, View, ViewGroup)}.
*
* @param view The view whose scroll state is being reported
*
* @param scrollState The current scroll state. One of
* {@link #SCROLL_STATE_TOUCH_SCROLL} or {@link #SCROLL_STATE_IDLE}.
*/
public void onScrollStateChanged(AbsListView view, int scrollState);
/**
* Callback method to be invoked when the list or grid has been scrolled. This will be
* called after the scroll has completed
* @param view The view whose scroll state is being reported
* @param firstVisibleItem the index of the first visible cell (ignore if
* visibleItemCount == 0)
* @param visibleItemCount the number of visible cells
* @param totalItemCount the number of items in the list adaptor
*/
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
int totalItemCount);
}
2.1 OnScrollSateChanged方法
OnScrollSateChanged根據(jù)scrollState來決定其回調(diào)的次數(shù),它有三種模式:
? OnScrollListener.SCROLL_STATE_IDLE:滾動停止時的狀態(tài)
? OnScrollListener.SCROLL_STATE_STOUCH_SCROLL:觸摸正在滾動,手指還沒離開界面時的狀態(tài)
? OnScrollListener.SCROLL_STATE_FLING:用戶在用力滑動后,ListView由于慣性將繼續(xù)滑動時的狀態(tài)
當(dāng)用戶沒有用力滑動時,OnScrollSateChanged方法只會回調(diào)2次,否則回調(diào)三次,我們在使用時通常會以設(shè)置Flag標(biāo)志,來區(qū)分不同的滑動狀態(tài),從而進(jìn)行相應(yīng)的處理
2.2 OnScroll方法
在ListView滾動時會一直被回調(diào),它通過里面有三個參數(shù)來顯示當(dāng)前ListView的滾動狀態(tài)
? firstVisibleItem:當(dāng)前能看見的第一個item的ID(從0開始)
? visibleItemCount:當(dāng)前可見的item總數(shù)
? totalItemCount:列表中適配器總數(shù)量,也就是整個ListView中item總數(shù)
注意:當(dāng)前可見的item總數(shù),包括屏幕中沒有顯示完整的item,如顯示一半的item也會算在可見范圍內(nèi)
通過這三個參數(shù),我么可以實(shí)現(xiàn)很多事件判斷,如:
(1)判斷當(dāng)前是否滑動到最后一行
當(dāng)前視圖中第一個item的ID加上當(dāng)前屏幕中可見item的總數(shù)如果等于ListView中所有item總數(shù)時,就表示移動到了最后一行
if (firstVisibleItem + visibleItemCount == totalItemCount && totalItemCount > 0) {
// 滾動到最后一行了
}
(2)判斷滑動的方向
通過oldVisibleItem 記錄上一次firstVisibleItem的位置,再與滑動后的firstVisibleItem進(jìn)行比較,就可得知滑動的方向
if (firstVisibleItem > oldVisibleItem) {
// 向上滑動
}
if (firstVisibleItem < oldVisibleItem) {
// 向下滑動
}
oldVisibleItem = firstVisibleItem;
ListView也為我們提供了一些封裝好了的方法,來獲取item的位置信息
// 獲取當(dāng)前可見區(qū)域內(nèi)第一個item的id
mListView.getFirstVisiblePosition();
// 獲取當(dāng)前可見區(qū)域內(nèi)最后一個item的id
mListView.getLastVisiblePosition();
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