NestedScrollingParent, NestedScrollingChild 详解
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NestedScrollingParent
NestedScrollingChild
这是两个接口, Android 就是通过这两个接口, 来实现 子View 与父View 之间的嵌套滑动
这样的嵌套滑动机制是在 Android 发布 Lollipop 之后提供的
不过同样在Support v7 中同样支持了
同时 RecycleView 以及 Android 5.0 以上的系统原声View 大部分都已经支持 嵌套滑动了
ok 了解个大概 下面来看看 具体的嵌套滑动 是怎样的:
想要理解 嵌套滑动
必须, 需要理解一下几个类(接口):
NestedScrollingChild
NestedScrollingParent
NestedScrollingChildHelper
NestedScrollingParentHelper
先来看 NestedScrollingChild 接口, 顾名思义, 这个是子View 应该实现 的接口:
先看源码
- public interface NestedScrollingChild {
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- public void setNestedScrollingEnabled(boolean enabled);
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- public boolean isNestedScrollingEnabled();
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- public boolean startNestedScroll(int axes);
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- public void stopNestedScroll();
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- public boolean hasNestedScrollingParent();
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- public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
- int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow);
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- public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow);
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- public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed);
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- public boolean dispatchNestedPreFling(float velocityX, float velocityY);
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去掉了 原来的注释, 加入点自己理解的注释
在看看 NestedScrollingParentHelper 这个类,
这个类是一个辅助类, 先来看看 子View 如何继承 NestedScrollingChild
- public class Child extends LinearLayout implements android.support.v4.view.NestedScrollingChild {
- public static final String TAG = "Child";
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- private NestedScrollingChildHelper mNestedScrollingChildHelper;
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- public Child(Context context, AttributeSet attrs) {
- super(context, attrs);
- mNestedScrollingChildHelper = new NestedScrollingChildHelper(this);
- }
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- @Override
- public void setNestedScrollingEnabled(boolean enabled) {
- mNestedScrollingChildHelper.setNestedScrollingEnabled(enabled);
- }
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- @Override
- public boolean isNestedScrollingEnabled() {
- return mNestedScrollingChildHelper.isNestedScrollingEnabled();
- }
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- @Override
- public boolean startNestedScroll(int axes) {
- return mNestedScrollingChildHelper.startNestedScroll(axes);
- }
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- @Override
- public void stopNestedScroll() {
- mNestedScrollingChildHelper.stopNestedScroll();
- }
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- @Override
- public boolean hasNestedScrollingParent() {
- return mNestedScrollingChildHelper.hasNestedScrollingParent();
- }
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- @Override
- public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
- return mNestedScrollingChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, offsetInWindow);
- }
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- @Override
- public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
- return mNestedScrollingChildHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow);
- }
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- @Override
- public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
- return mNestedScrollingChildHelper.dispatchNestedFling(velocityX, velocityY, consumed);
- }
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- @Override
- public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
- return mNestedScrollingChildHelper.dispatchNestedPreFling(velocityX, velocityY);
- }
- }
可以看到基本接口里面的每个方法 都只要调用 mNestedScrollingChildHelper 中相应的方法;
下面来看看 NestedScrollingParentHelper 源码:
- public class NestedScrollingChildHelper {
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- private final View mView;
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- private ViewParent mNestedScrollingParent;
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- private boolean mIsNestedScrollingEnabled;
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- private int[] mTempNestedScrollConsumed;
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- public NestedScrollingChildHelper(View view) {
- mView = view;
- }
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- public void setNestedScrollingEnabled(boolean enabled) {
- if (mIsNestedScrollingEnabled) {
- ViewCompat.stopNestedScroll(mView);
- }
- mIsNestedScrollingEnabled = enabled;
- }
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- public boolean isNestedScrollingEnabled() {
- return mIsNestedScrollingEnabled;
- }
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- public boolean hasNestedScrollingParent() {
- return mNestedScrollingParent != null;
- }
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- public boolean startNestedScroll(int axes) {
- if (hasNestedScrollingParent()) {
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- return true;
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- if (isNestedScrollingEnabled()) {
- ViewParent p = mView.getParent();
- View child = mView;
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- while (p != null) {
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- if (ViewParentCompat.onStartNestedScroll(p, child, mView, axes)) {
- mNestedScrollingParent = p;
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- ViewParentCompat.onNestedScrollAccepted(p, child, mView, axes);
- return true;
- }
- if (p instanceof View) {
- child = (View) p;
- }
- p = p.getParent();
- }
- }
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- return false;
- }
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- public void stopNestedScroll() {
- if (mNestedScrollingParent != null) {
- ViewParentCompat.onStopNestedScroll(mNestedScrollingParent, mView);
- mNestedScrollingParent = null;
- }
- }
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- public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
- int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
- if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
- if (dxConsumed != 0 || dyConsumed != 0 || dxUnconsumed != 0 || dyUnconsumed != 0) {
- int startX = 0;
- int startY = 0;
- if (offsetInWindow != null) {
- mView.getLocationInWindow(offsetInWindow);
- startX = offsetInWindow[0];
- startY = offsetInWindow[1];
- }
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- ViewParentCompat.onNestedScroll(mNestedScrollingParent, mView, dxConsumed,
- dyConsumed, dxUnconsumed, dyUnconsumed);
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- if (offsetInWindow != null) {
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- mView.getLocationInWindow(offsetInWindow);
- offsetInWindow[0] -= startX;
- offsetInWindow[1] -= startY;
- }
- return true;
- } else if (offsetInWindow != null) {
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- offsetInWindow[0] = 0;
- offsetInWindow[1] = 0;
- }
- }
- return false;
- }
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- public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
- if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
- if (dx != 0 || dy != 0) {
- int startX = 0;
- int startY = 0;
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- if (offsetInWindow != null) {
- mView.getLocationInWindow(offsetInWindow);
- startX = offsetInWindow[0];
- startY = offsetInWindow[1];
- }
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- if (consumed == null) {
- if (mTempNestedScrollConsumed == null) {
- mTempNestedScrollConsumed = new int[2];
- }
- consumed = mTempNestedScrollConsumed;
- }
- consumed[0] = 0;
- consumed[1] = 0;
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- ViewParentCompat.onNestedPreScroll(mNestedScrollingParent, mView, dx, dy, consumed);
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- if (offsetInWindow != null) {
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- mView.getLocationInWindow(offsetInWindow);
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- offsetInWindow[0] -= startX;
- offsetInWindow[1] -= startY;
- }
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- return consumed[0] != 0 || consumed[1] != 0;
- } else if (offsetInWindow != null) {
- offsetInWindow[0] = 0;
- offsetInWindow[1] = 0;
- }
- }
- return false;
- }
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- public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
- if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
- return ViewParentCompat.onNestedFling(mNestedScrollingParent, mView, velocityX,
- velocityY, consumed);
- }
- return false;
- }
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- public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
- if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
- return ViewParentCompat.onNestedPreFling(mNestedScrollingParent, mView, velocityX,
- velocityY);
- }
- return false;
- }
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- public void onDetachedFromWindow() {
- ViewCompat.stopNestedScroll(mView);
- }
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- public void onStopNestedScroll(View child) {
- ViewCompat.stopNestedScroll(mView);
- }
- }
从上面的注释 可以基本看到 嵌套滑动的基本逻辑:
下面来看看 父View
- public class Parent extends LinearLayout implements NestedScrollingParent {
- public static final String TAG = "Parent";
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- private NestedScrollingParentHelper mNestedScrollingParentHelper;
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- public Parent(Context context, AttributeSet attrs) {
- super(context, attrs);
- mNestedScrollingParentHelper = new NestedScrollingParentHelper(this);
- }
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- @Override
- public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) {
- return true;
- }
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- @Override
- public void onNestedScrollAccepted(View child, View target, int nestedScrollAxes) {
- mNestedScrollingParentHelper.onNestedScrollAccepted(child, target, nestedScrollAxes);
- }
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- @Override
- public void onStopNestedScroll(View target) {
- mNestedScrollingParentHelper.onStopNestedScroll(target);
- }
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- @Override
- public void onNestedScroll(View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) {
- LogUtil.d(TAG, "onNestedScroll target = " + target + " , dxConsumed = " + dxConsumed + " , dyConsumed = " + dyConsumed + " , dxUnconsumed = " + dxUnconsumed + " , dyUnconsumed = " + dyUnconsumed);
- }
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- @Override
- public void onNestedPreScroll(View target, int dx, int dy, int[] consumed) {
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- consumed[1] = dy;
- LogUtil.d(TAG, "onNestedPreScroll dx = " + dx + " dy = " + dy);
- }
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- @Override
- public boolean onNestedFling(View target, float velocityX, float velocityY, boolean consumed) {
- return false;
- }
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- @Override
- public boolean onNestedPreFling(View target, float velocityX, float velocityY) {
- return false;
- }
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- @Override
- public int getNestedScrollAxes() {
- return mNestedScrollingParentHelper.getNestedScrollAxes();
- }
- }
总结一下 整个嵌套滑动的流程是:
子view父viewstartNestedScrollonStartNestedScroll、onNestedScrollAccepteddispatchNestedPreScrollonNestedPreScrolldispatchNestedScrollonNestedScrollstopNestedScrollonStopNestedScroll
通过以上的代码 注释 基本对 嵌套互动有了一个大致的基本了解
转载地址:http://blog.csdn.net/chen930724/article/details/50307193
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