Android ScrollView滑动监听
因为项目里用到了ScrollView， 并需要实现类似于ListView的滑动监听回调，所以自定义了一套实现方式支持这些事件， 基本满足了业务需求；
public interface OnMyScrollListener {
int SCROLL_STATE_FLING = 2; //手指滑动后松开，自动滑动
int SCROLL_STATE_IDLE = 0; //不滑动
int SCROLL_STATE_TOUCH_SCROLL = 1; //手指按着屏幕滑动
void onScrollStateChanged(MyScrollView view, int state);
void onScroll(MyScrollView view, int y); //滑动距离
void onScrollToTop(); //滑到顶部
void onScrollToBottom(); //滑到底部
}原理：
1、判断fling？ ScrollView的fling都会执行ScrollView.fling函数， 所以覆盖该函数并在函数体执行回调， 表示已开始fling；
2、判断drag？ ScrollView有个成员变量mIsBeingDragged, 覆盖onTouch函数判断MOVE事件时反射读取该参数；
/**
* True if the user is currently dragging this ScrollView around. This is
* not the same as 'is being flinged', which can be checked by
* mScroller.isFinished() (flinging begins when the user lifts his finger).
*/
private boolean mIsBeingDragged = false;
3、判断idle？ 网络上有2个方法： 1、使用延迟消息，判断scroll位置是否发生变化（比较靠谱）； 2、反射读取OverScroller的isFinished函数（不靠谱）。 我是用onDraw函数实现的， 滑动结束时会执行多次onDraw函数；
4、判断滑到顶部？ 判断scrollY等于0， 即滑动距离为0；
5、判断滑到底部？ ScrollView本身高度+上下间距+滑动距离 等于 子View 高度；
日志：
07-08 07:24:49.540 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动状态：IDLE
07-08 07:24:49.847 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动底部
07-08 07:24:51.894 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动状态：DRAG
07-08 07:24:51.931 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动状态：FLING
07-08 07:24:52.975 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动状态：IDLE
滑到顶部
07-08 07:24:54.757 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动状态：DRAG
07-08 07:24:54.812 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动状态：FLING
07-08 07:24:55.219 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动状态：IDLE
07-08 07:24:55.526 8388-8388/com.byrcegao.myscrollviewtest D/brycegao: 滑动底部完整代码：
public class MainActivity extends Activity {
private MyScrollView scrollView;
private MyScrollView.OnMyScrollListener listener;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
scrollView = (MyScrollView) findViewById(R.id.myscrollview);
listener = new MyScrollView.OnMyScrollListener() {
@Override public void onScrollStateChanged(MyScrollView view, int state) {
String str;
if (state == 0) {
str = "IDLE";
} else if (state == 1) {
str = "DRAG";
} else if (state == 2) {
str = "FLING";
} else {
str = "ERROR";
}
Log.d("brycegao", "滑动状态：" + str);
}
@Override public void onScroll(MyScrollView view, int y) {
}
@Override public void onScrollToTop() {
Log.d("brycegao", "滑到顶部");
}
@Override public void onScrollToBottom() {
Log.d("brycegao", "滑动底部");
}
};
}
@Override protected void onResume() {
super.onResume();
scrollView.addOnScrollListner(listener);
}
@Override public void onLocalVoiceInteractionStopped() {
super.onLocalVoiceInteractionStopped();
scrollView.removeOnScrollListener(listener);
}
}package com.byrcegao.myscrollviewtest;
import android.content.Context;
import android.graphics.Canvas;
import android.os.Build;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.FrameLayout;
import android.widget.ScrollView;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
/**
* 自定义ScrollView滑动事件
* @author brycegao
*/
public class MyScrollView extends ScrollView {
private ArrayList listeners;
private int currentState;
private boolean isLastBottom; //上次刷新是否底部
private int lastDrawPos; //上次刷新的纵向位移
public interface OnMyScrollListener {
int SCROLL_STATE_FLING = 2; //手指滑动后松开，自动滑动
int SCROLL_STATE_IDLE = 0; //不滑动
int SCROLL_STATE_TOUCH_SCROLL = 1; //手指按着屏幕滑动
void onScrollStateChanged(MyScrollView view, int state);
void onScroll(MyScrollView view, int y); //滑动距离
void onScrollToTop(); //滑到顶部
void onScrollToBottom(); //滑到底部
}
public MyScrollView(Context context) {
super(context);
}
public MyScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
listeners = new ArrayList<>();
}
public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override public boolean onTouchEvent(MotionEvent ev) {
boolean lastDragState = getDragState();
boolean ret = super.onTouchEvent(ev);
if (ev.getActionMasked() == MotionEvent.ACTION_MOVE) {
for (OnMyScrollListener listener:listeners) {
listener.onScroll(this, getScrollY());
}
}
if ((ev.getActionMasked() == MotionEvent.ACTION_UP
|| ev.getActionMasked() == MotionEvent.ACTION_CANCEL)
&& currentState == OnMyScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
//取消滑动
currentState = OnMyScrollListener.SCROLL_STATE_IDLE;
for (OnMyScrollListener listener:listeners) {
listener.onScrollStateChanged(this, OnMyScrollListener.SCROLL_STATE_IDLE);
}
}
boolean curDragState = getDragState();
//拖动
if (!lastDragState && curDragState) {
currentState = OnMyScrollListener.SCROLL_STATE_TOUCH_SCROLL;
for (OnMyScrollListener listener:listeners) {
listener.onScrollStateChanged(this, OnMyScrollListener.SCROLL_STATE_TOUCH_SCROLL);
}
}
return ret;
}
@Override protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (lastDrawPos == getScrollY()
&& getScrollY() > 0
&& currentState == OnMyScrollListener.SCROLL_STATE_FLING ) {
currentState = OnMyScrollListener.SCROLL_STATE_IDLE; //设置状态为空闲
for (OnMyScrollListener listener:listeners) {
listener.onScrollStateChanged(this, OnMyScrollListener.SCROLL_STATE_IDLE);
}
}
if (getScrollY() == 0 && lastDrawPos == 0
&& currentState != OnMyScrollListener.SCROLL_STATE_IDLE) {
currentState = OnMyScrollListener.SCROLL_STATE_IDLE; //设置状态为空闲
for (OnMyScrollListener listener:listeners) {
listener.onScrollStateChanged(this, OnMyScrollListener.SCROLL_STATE_IDLE);
listener.onScrollToTop();
}
}
lastDrawPos = getScrollY();
if (isCurrentBottom()
&& !isLastBottom) {
for (OnMyScrollListener listener:listeners) {
listener.onScrollToBottom();
}
}
isLastBottom = isCurrentBottom();
}
@Override public void fling(int velocityY) {
super.fling(velocityY);
if (getChildCount() > 0) {
currentState = OnMyScrollListener.SCROLL_STATE_FLING;
for (OnMyScrollListener listener:listeners) {
listener.onScrollStateChanged(this, OnMyScrollListener.SCROLL_STATE_FLING);
}
}
}
//判断是否滑到底部
private boolean isCurrentBottom() {
boolean ret = false;
int targetSdkVersion = getContext().getApplicationInfo().targetSdkVersion;
int heightPadding; //scrollview上下padding之和
View child = getChildAt(0);
final FrameLayout.LayoutParams lp = (LayoutParams) child.getLayoutParams();
if (targetSdkVersion >= Build.VERSION_CODES.M) {
heightPadding = getPaddingTop() + getPaddingBottom() + lp.topMargin + lp.bottomMargin;
} else {
heightPadding = getPaddingTop() + getPaddingBottom();
}
if (getMeasuredHeight() - heightPadding + getScrollY() == child.getMeasuredHeight()) {
ret = true;
}
return ret;
}
//反射查询mIsBeingDragged
private boolean getDragState() {
boolean state = false;
try {
Class clz = ScrollView.class;
Field field = clz.getDeclaredField("mIsBeingDragged");
field.setAccessible(true);
state = field.getBoolean(this);
} catch (Exception ex) {
ex.printStackTrace();
}
return state;
}
//滑动加速器是否停止
private boolean isfinishScroll() {
boolean isfinish=false;
Class scrollview=ScrollView.class;
try {
Field scrollField=scrollview.getDeclaredField("mScroller");
scrollField.setAccessible(true);
Object scroller=scrollField.get(this);
Class overscroller= scrollField.getType();
Method finishField=overscroller.getMethod("isFinished");
finishField.setAccessible(true);
isfinish= (boolean) finishField.invoke(scroller);
} catch (NoSuchFieldException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
} catch (InvocationTargetException e) {
e.printStackTrace();
}
return isfinish;
}
/**
* 添加滑动监听
* @param listener
*/
public void addOnScrollListner(OnMyScrollListener listener) {
if (listener == null) {
throw new IllegalArgumentException("invalid listener");
}
if (!listeners.contains(listener)) {
listeners.add(listener);
}
}
public void removeOnScrollListener(OnMyScrollListener listener) {
if (listener == null) {
throw new IllegalArgumentException("invalid listener");
}
listeners.remove(listener);
}
}