CollapsingToolbarLayout 折叠时滚动停止

Question

我将 CoordinatorLayout 与 AppBarLayout 和 CollapsingToolbarLayout 一起使用。还有一个 NestedScrollView 用于内容。当我在 CollapsingToolbarLayout 上进行滚动时，当 CollapsingToolbarLayout 折叠时滚动停止。我想要的是继续滚动 NestedScrollView 的内容。当我在 NestedScrollView 上进行滚动时，它会一直滚动到内容的末尾。 CollapsingToolbarLayout 按预期折叠。

视频链接：http://sendvid.com/m7d0mq2q

在视频中，正如您在第一次滚动中看到的那样，当 CollapsingToolbarLayout 折叠时它会停止滚动。

我的布局：

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.journaldev.collapsingtoolbarlayout.ScrollingActivity">

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/app_bar"
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:fitsSystemWindows="true"
        android:theme="@style/AppTheme.AppBarOverlay">

        <com.google.android.material.appbar.CollapsingToolbarLayout
            android:id="@+id/toolbar_layout"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true"
            app:contentScrim="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|exitUntilCollapsed">


            <ImageView
                android:id="@+id/expandedImage"
                android:layout_width="match_parent"
                android:layout_height="400dp"
                android:scaleType="centerCrop"
                android:src="@drawable/photo"/>

            <androidx.appcompat.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/AppTheme.PopupOverlay" />

        </com.google.android.material.appbar.CollapsingToolbarLayout>
    </com.google.android.material.appbar.AppBarLayout>

    <androidx.core.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="@dimen/text_margin"
            android:text="@string/large_text" />

    </androidx.core.widget.NestedScrollView>

</androidx.coordinatorlayout.widget.CoordinatorLayout>

我的活动：

package com.journaldev.collapsingtoolbarlayout;

import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import com.google.android.material.appbar.AppBarLayout;

public class ScrollingActivity extends AppCompatActivity {


    private Menu menu;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scrolling);
        final Toolbar mToolbar = this.findViewById(R.id.toolbar);
        setSupportActionBar(mToolbar);

        AppBarLayout mAppBarLayout = (AppBarLayout) findViewById(R.id.app_bar);
        mAppBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
            boolean isShow = false;
            int scrollRange = -1;

            @Override
            public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
                if (scrollRange == -1) {
                    scrollRange = appBarLayout.getTotalScrollRange();
                }
                if (scrollRange + verticalOffset == 0) {
                    isShow = true;
                    showOption(R.id.action_info);
                } else if (isShow) {
                    isShow = false;
                    hideOption(R.id.action_info);
                }
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        this.menu = menu;
        getMenuInflater().inflate(R.menu.menu_scrolling, menu);
        hideOption(R.id.action_info);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        } else if (id == R.id.action_info) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    private void hideOption(int id) {
        MenuItem item = menu.findItem(id);
        item.setVisible(false);
    }

    private void showOption(int id) {
        MenuItem item = menu.findItem(id);
        item.setVisible(true);
    }
}

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    buildToolsVersion "25.0.2"
    defaultConfig {
        applicationId "com.journaldev.collapsingtoolbarlayout"
        minSdkVersion 21
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    implementation "androidx.appcompat:appcompat:1.0.2"
    implementation "com.google.android.material:material:1.1.0-alpha04"
    testCompile 'junit:junit:4.12'
}

Answer 1

当我们在滚动视图（即RecyclerView）上进行投掷时，一切都按预期工作。所以我的解决方案的想法是忽略AppBarLayout 的投掷并将完全相同的参数传递给滚动视图（在我的情况下是RecyclerView）。所以，我们只需要为这个类提供适当的滚动视图（很可能，它也适用于其他视图，即NestedScrollView）。作为奖励，我的自定义行为不仅解决了大多数华为设备上出现的丑陋抖动问题（如果不感兴趣，只需删除 onNestedPreFling 方法）。有关此问题的更多详细信息：CollapsingToolbarLayout flickers while scrolling down

/**
 * Customized app bar provides 2 features:
 * 1. Force AppBarLayout to stop fling when nested view starts fling, otherwise scrolling view fling collides with AppBarLayout fling
 * 2. Ignore AppBarLayout fling and transfer it to scrolling view. This is done in order to continue page scroll when AppBarLayout
 * fully collapses (now after collapse scroll stops)
 */

class SmoothAppBarBehavior : AppBarLayout.Behavior() {

    companion object {
        private const val FLING_UNITS = 1000 //copied from base class
    }

    var recyclerView: RecyclerView? = null
    private var overScroller: OverScroller? = null
    private var pointerId = -1
    private var velocityTracker: VelocityTracker? = null

    override fun onNestedPreFling(coordinatorLayout: CoordinatorLayout,
                                  child: AppBarLayout,
                                  target: View,
                                  velocityX: Float,
                                  velocityY: Float): Boolean {
        stopAppBarLayoutFling()
        return super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY)
    }

    override fun onInterceptTouchEvent(parent: CoordinatorLayout,
                                       child: AppBarLayout,
                                       ev: MotionEvent): Boolean {
        val consumed = super.onInterceptTouchEvent(parent, child, ev)
        when (ev.actionMasked) {
            MotionEvent.ACTION_DOWN -> {
                ensureVelocityTracker()              
                recyclerView?.stopScroll()
                pointerId = ev.getPointerId(0)
            }
            MotionEvent.ACTION_CANCEL -> {
                velocityTracker?.recycle()
                velocityTracker = null
                pointerId = -1
            }
            else -> {}
        }
        return consumed
    }

    override fun onTouchEvent(parent: CoordinatorLayout,
                              child: AppBarLayout,
                              ev: MotionEvent): Boolean {
        val consumed = super.onTouchEvent(parent, child, ev)
        recyclerView?.let {
            when (ev.actionMasked) {
                MotionEvent.ACTION_DOWN -> {
                    ensureVelocityTracker()
                    pointerId = ev.getPointerId(0)
                }
                MotionEvent.ACTION_UP -> {
                    stopAppBarLayoutFling()
                    recyclerView?.fling(0, getYVelocity(ev))
                }
                MotionEvent.ACTION_CANCEL -> {
                    velocityTracker?.recycle()
                    velocityTracker = null
                    pointerId = -1
                }
                else -> {}
            }
            velocityTracker?.addMovement(ev)
        }
        return consumed
    }

    private fun ensureVelocityTracker() {
        if (velocityTracker == null) {
            velocityTracker = VelocityTracker.obtain()
        }
    }

    private fun getYVelocity(event: MotionEvent): Int {
        velocityTracker?.let {
            it.addMovement(event)
            it.computeCurrentVelocity(FLING_UNITS)
            return - it.getYVelocity(pointerId).toInt()
        }
        return 0
    }

    private fun stopAppBarLayoutFling() {
        if (overScroller == null) {
            val scrollerField = javaClass.superclass.superclass.superclass.getDeclaredField("scroller")
            scrollerField.isAccessible = true
            overScroller = scrollerField.get(this) as? OverScroller
        }
        overScroller?.forceFinished(true)
    }
}