編輯：關於Android編程
View的滑動沖突指的是當有內外兩層View同時可以滑動的時候，這個時候就會產生滑動沖突。那麼應該如何解決滑動呢，其實要用到View的事件分發機制。
View的滑動沖突主要有以下三個場景：
場景一：外部滑動方向和內部滑動方向不一致；
場景二：外部滑動方向和內部滑動方向一致；
場景三：以上兩種情況的嵌套。
這裡主要討論場景一的滑動沖突的解決，其他兩種思想都是類似的，根據具體情況而定。
對於場景一，它的滑動沖突處理規則是：當用戶左右滑動時，需要外部的View攔截點擊事件，當用戶上下滑動時，需要內部的View攔截點擊事件。解決滑動沖突的思想就是根據滑動郭晨各種兩個點之間的坐標就可以得出到底是水平滑動還是豎直滑動。那麼如何判斷是水平滑動還是豎直滑動呢？這個有很多參考，比如我們可以根據水平方向和豎直方向的距離差來判斷，某些情況還可以根據速度差來判斷。這裡根據距離差來處理滑動沖突。
當水平方向的滑動距離大於豎直方向的滑動距離時，判斷為水平滑動，否則判斷為豎直滑動。如下圖所示
也就是當dx > dy時判斷為水平滑動，否則為豎直滑動。針對滑動沖突，這裡給出兩種解決滑動沖突的方式：外部攔截法，內部攔截法。
1、外部攔截法
所謂外部攔截法是指點擊事件都先經過父容器的攔截處理，如果父容器需要此事件就攔截，如果不需要此事件就不攔截，這樣就可以解決滑動沖突的問題。這種方法也比較符合點擊事件的分發機制。外部攔截發需要重寫父容器的onInterceptTouchEvent方法，在內部做相應的攔截即可，偽代碼如下。
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
boolean intercepted = false;
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
intercepted = false;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
intercepted = true;
}
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastXIntercept;
int deltaY = y - mLastYIntercept;
if (父容器需要當前點擊事件) {
intercepted = true;
} else {
intercepted = false;
}
break;
}
case MotionEvent.ACTION_UP: {
intercepted = false;
break;
}
default:
break;
}
Log.d(TAG, "intercepted=" + intercepted);
mLastX = x;
mLastY = y;
mLastXIntercept = x;
mLastYIntercept = y;
return intercepted;
}
另外針對上述代碼再說明一下，
首先down事件，父容器必須返回false，即不攔截down事件，如果攔截了down事件，那麼後續的move和up事件都交給父容器處理了，不存在什麼滑動了，也就是不存在什麼滑動沖突的解決了，更不能將事件傳遞給子元素。
然後是move事件，這是我們要處理的核心事件，這個時候需要根據具體需要看判斷是否要攔截事件。如果父容器需要就攔截，不需要就不攔截。
最後是up事件，必須要返回false，因為本身沒有什麼意義。考慮一種情況，假設父容器up返回了true，那麼元素的onClick事件無法觸發。
為了實現場景一的效果，定義了一個類似於水平的LinearLayout的東西，只不過它可以水平滑動，初始化時我們在它的內部添加若干個ListView，這樣一來，由於它內部的ListView可以豎直滑動，而它本身又可以水平滑動，因此一個典型的場景一滑動沖突就出現了，這裡根據水平和豎直距離差來判斷。
首先貼上Activity代碼：
package com.ryg.chapter_3;
import java.util.ArrayList;
import com.ryg.chapter_3.R;
import com.ryg.chapter_3.ui.HorizontalScrollViewEx;
import com.ryg.chapter_3.utils.MyUtils;
import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;
public class DemoActivity_1 extends Activity {
private static final String TAG = "DemoActivity_1";
private HorizontalScrollViewEx mListContainer;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.demo_1);
Log.d(TAG, "onCreate");
initView();
}
private void initView() {
LayoutInflater inflater = getLayoutInflater();
mListContainer = (HorizontalScrollViewEx) findViewById(R.id.container);
final int screenWidth = MyUtils.getScreenMetrics(this).widthPixels;
final int screenHeight = MyUtils.getScreenMetrics(this).heightPixels;
for (int i = 0; i < 3; i++) {
ViewGroup layout = (ViewGroup) inflater.inflate(
R.layout.content_layout, mListContainer, false);
layout.getLayoutParams().width = screenWidth;
TextView textView = (TextView) layout.findViewById(R.id.title);
textView.setText("page " + (i + 1));
layout.setBackgroundColor(Color.rgb(255 / (i + 1), 255 / (i + 1), 0));
createList(layout);
mListContainer.addView(layout);
}
}
private void createList(ViewGroup layout) {
ListView listView = (ListView) layout.findViewById(R.id.list);
ArrayList<String> datas = new ArrayList<String>();
for (int i = 0; i < 50; i++) {
datas.add("name " + i);
}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
R.layout.content_list_item, R.id.name, datas);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
Toast.makeText(DemoActivity_1.this, "click item",
Toast.LENGTH_SHORT).show();
}
});
}
}
采用外部攔截法，它的onInterceptTouchEvent方法如下：
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
boolean intercepted = false;
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
intercepted = false;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
intercepted = true;
}
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastXIntercept;
int deltaY = y - mLastYIntercept;
if (Math.abs(deltaX) > Math.abs(deltaY)) {
intercepted = true;
} else {
intercepted = false;
}
break;
}
case MotionEvent.ACTION_UP: {
intercepted = false;
break;
}
default:
break;
}
Log.d(TAG, "intercepted=" + intercepted);
mLastX = x;
mLastY = y;
mLastXIntercept = x;
mLastYIntercept = y;
return intercepted;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
mVelocityTracker.addMovement(event);
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastX;
int deltaY = y - mLastY;
scrollBy(-deltaX, 0);
break;
}
case MotionEvent.ACTION_UP: {
int scrollX = getScrollX();
int scrollToChildIndex = scrollX / mChildWidth;
mVelocityTracker.computeCurrentVelocity(1000);
float xVelocity = mVelocityTracker.getXVelocity();
if (Math.abs(xVelocity) >= 50) {
mChildIndex = xVelocity > 0 ? mChildIndex - 1 : mChildIndex + 1;
} else {
mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;
}
mChildIndex = Math.max(0, Math.min(mChildIndex, mChildrenSize - 1));
int dx = mChildIndex * mChildWidth - scrollX;
smoothScrollBy(dx, 0);
mVelocityTracker.clear();
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return true;
}
HorizontalScrollViewEx的完整代碼如下;代碼參考了Android開發藝術探索一書。
package com.ryg.chapter_3.ui;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Scroller;
public class HorizontalScrollViewEx extends ViewGroup {
private static final String TAG = "HorizontalScrollViewEx";
private int mChildrenSize;
private int mChildWidth;
private int mChildIndex;
// 分別記錄上次滑動的坐標
private int mLastX = 0;
private int mLastY = 0;
// 分別記錄上次滑動的坐標(onInterceptTouchEvent)
private int mLastXIntercept = 0;
private int mLastYIntercept = 0;
private Scroller mScroller;
private VelocityTracker mVelocityTracker;
public HorizontalScrollViewEx(Context context) {
super(context);
init();
}
public HorizontalScrollViewEx(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public HorizontalScrollViewEx(Context context, AttributeSet attrs,
int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
mScroller = new Scroller(getContext());
mVelocityTracker = VelocityTracker.obtain();
}
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
boolean intercepted = false;
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
intercepted = false;
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
intercepted = true;
}
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastXIntercept;
int deltaY = y - mLastYIntercept;
if (Math.abs(deltaX) > Math.abs(deltaY)) {
intercepted = true;
} else {
intercepted = false;
}
break;
}
case MotionEvent.ACTION_UP: {
intercepted = false;
break;
}
default:
break;
}
Log.d(TAG, "intercepted=" + intercepted);
mLastX = x;
mLastY = y;
mLastXIntercept = x;
mLastYIntercept = y;
return intercepted;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
mVelocityTracker.addMovement(event);
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
break;
}
case MotionEvent.ACTION_MOVE: {
int deltaX = x - mLastX;
int deltaY = y - mLastY;
scrollBy(-deltaX, 0);
break;
}
case MotionEvent.ACTION_UP: {
int scrollX = getScrollX();
int scrollToChildIndex = scrollX / mChildWidth;
mVelocityTracker.computeCurrentVelocity(1000);
float xVelocity = mVelocityTracker.getXVelocity();
if (Math.abs(xVelocity) >= 50) {
mChildIndex = xVelocity > 0 ? mChildIndex - 1 : mChildIndex + 1;
} else {
mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;
}
mChildIndex = Math.max(0, Math.min(mChildIndex, mChildrenSize - 1));
int dx = mChildIndex * mChildWidth - scrollX;
smoothScrollBy(dx, 0);
mVelocityTracker.clear();
break;
}
default:
break;
}
mLastX = x;
mLastY = y;
return true;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int measuredWidth = 0;
int measuredHeight = 0;
final int childCount = getChildCount();
measureChildren(widthMeasureSpec, heightMeasureSpec);
int widthSpaceSize = MeasureSpec.getSize(widthMeasureSpec);
int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
int heightSpaceSize = MeasureSpec.getSize(heightMeasureSpec);
int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
if (childCount == 0) {
setMeasuredDimension(0, 0);
} else if (heightSpecMode == MeasureSpec.AT_MOST) {
final View childView = getChildAt(0);
measuredHeight = childView.getMeasuredHeight();
setMeasuredDimension(widthSpaceSize, childView.getMeasuredHeight());
} else if (widthSpecMode == MeasureSpec.AT_MOST) {
final View childView = getChildAt(0);
measuredWidth = childView.getMeasuredWidth() * childCount;
setMeasuredDimension(measuredWidth, heightSpaceSize);
} else {
final View childView = getChildAt(0);
measuredWidth = childView.getMeasuredWidth() * childCount;
measuredHeight = childView.getMeasuredHeight();
setMeasuredDimension(measuredWidth, measuredHeight);
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childLeft = 0;
final int childCount = getChildCount();
mChildrenSize = childCount;
for (int i = 0; i < childCount; i++) {
final View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE) {
final int childWidth = childView.getMeasuredWidth();
mChildWidth = childWidth;
childView.layout(childLeft, 0, childLeft + childWidth,
childView.getMeasuredHeight());
childLeft += childWidth;
}
}
}
private void smoothScrollBy(int dx, int dy) {
mScroller.startScroll(getScrollX(), 0, dx, 0, 500);
invalidate();
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
@Override
protected void onDetachedFromWindow() {
mVelocityTracker.recycle();
super.onDetachedFromWindow();
}
}
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