Android 自定义WebView 实现 NestedScrollingChild

有时候我们需要webview实现NestedScrollingChild那样的功能，原生webview不支持，只能通过自定义webview实现NestedScrollingChild接口来实现。

由于本人自定义view水平有限，实现不了该功能。好在国外的大神Tobias Rohloff 实现了该功能，在此谢谢他。

详细代码如下：

/*
* Copyright (C) 2016 Tobias Rohloff
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0 *
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.tobiasrohloff.view;

import android.content.Context;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.NestedScrollingChild;
import android.support.v4.view.NestedScrollingChildHelper;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.webkit.WebView;

public class NestedScrollWebView extends WebView implements NestedScrollingChild {

public static final String TAG = NestedScrollWebView.class.getSimpleName();

private int mLastMotionY;

private final int[] mScrollOffset = new int[2];
private final int[] mScrollConsumed = new int[2];

private int mNestedYOffset;

private NestedScrollingChildHelper mChildHelper;

public NestedScrollWebView(Context context) {
super(context);
init();
}

public NestedScrollWebView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}

public NestedScrollWebView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}

private void init() {
mChildHelper = new NestedScrollingChildHelper(this);
setNestedScrollingEnabled(true);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
boolean result = false;

MotionEvent trackedEvent = MotionEvent.obtain(event);

final int action = MotionEventCompat.getActionMasked(event);

if (action == MotionEvent.ACTION_DOWN) {
mNestedYOffset = 0;
}

int y = (int) event.getY();

event.offsetLocation(0, mNestedYOffset);

switch (action) {
case MotionEvent.ACTION_DOWN:
mLastMotionY = y;
startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
result = super.onTouchEvent(event);
break;
case MotionEvent.ACTION_MOVE:
int deltaY = mLastMotionY - y;

if (dispatchNestedPreScroll(0, deltaY, mScrollConsumed, mScrollOffset)) {
deltaY -= mScrollConsumed[1];
trackedEvent.offsetLocation(0, mScrollOffset[1]);
mNestedYOffset += mScrollOffset[1];
}

int oldY = getScrollY();
mLastMotionY = y - mScrollOffset[1];
if (deltaY < 0) {
int newScrollY = Math.max(0, oldY + deltaY);
deltaY -= newScrollY - oldY;
if (dispatchNestedScroll(0, newScrollY - deltaY, 0, deltaY, mScrollOffset)) {
mLastMotionY -= mScrollOffset[1];
trackedEvent.offsetLocation(0, mScrollOffset[1]);
mNestedYOffset += mScrollOffset[1];
}
}

trackedEvent.recycle();
result = super.onTouchEvent(trackedEvent);
break;
case MotionEvent.ACTION_POINTER_DOWN:
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL:
stopNestedScroll();
result = super.onTouchEvent(event);
break;
}
return result;
}

// NestedScrollingChild

@Override
public void setNestedScrollingEnabled(boolean enabled) {
mChildHelper.setNestedScrollingEnabled(enabled);
}

@Override
public boolean isNestedScrollingEnabled() {
return mChildHelper.isNestedScrollingEnabled();
}

@Override
public boolean startNestedScroll(int axes) {
return mChildHelper.startNestedScroll(axes);
}

@Override
public void stopNestedScroll() {
mChildHelper.stopNestedScroll();
}

@Override
public boolean hasNestedScrollingParent() {
return mChildHelper.hasNestedScrollingParent();
}

@Override
public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
return mChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, offsetInWindow);
}

@Override
public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
return mChildHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow);
}

@Override
public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
return mChildHelper.dispatchNestedFling(velocityX, velocityY, consumed);
}

@Override
public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
return mChildHelper.dispatchNestedPreFling(velocityX, velocityY);
}

}

源码地址请点击这里哦