[移动开发]Android 在ScrollView中的导航栏悬浮吸顶方法实现（demo）

页面截图：

java代码：

MainActivity：

import androidx.appcompat.app.AppCompatActivity;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;

public class MainActivity extends AppCompatActivity implements MyScrollView.ScrollChangedListener {
    MyScrollView myScrollview;
    LinearLayout lineAddNavigationSuspension;
    LinearLayout lineAddNavigationFixation;
    View titleView;
    View navigation;
    int statusBarHeight;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myScrollview = findViewById(R.id.myScrollview);
        myScrollview.setListener(this::onScrollChanged);
        titleView = findViewById(R.id.titleView);
        navigation = findViewById(R.id.navigation);
        lineAddNavigationSuspension = findViewById(R.id.lineAddNavigationSuspension);
        lineAddNavigationFixation = findViewById(R.id.lineAddNavigationFixation);
    }


    @Override
    public void onScrollChanged(int scrollX, int scrollY, int oldl, int oldt) {
        int[] location = new int[2];
        lineAddNavigationFixation.getLocationOnScreen(location);
        //lineAddNavigationFixation是包裹导航栏的LinearLayout
        int y = location[1];//导航栏距屏幕顶部的距离，会随着scrollview的滑动而改变
        if (y <= titleView.getHeight() + getStatusHeight()) {//导航栏距屏幕顶部的距离小于等于标题栏的高度时 悬浮，即上滑到紧贴标题栏时 悬浮
            addNavigationSuspension();
        } else {//反之下滑到距离大于标题栏的高度时放回原来的位置
            addNavigationFixation();
        }

    }

    private void addNavigationSuspension() {
        if (lineAddNavigationSuspension.getChildCount() == 0) {

            if (navigation.getParent() != null)
                ((ViewGroup) navigation.getParent()).removeView(navigation);

            lineAddNavigationSuspension.addView(navigation);
        }
    }

    private void addNavigationFixation() {
        if (lineAddNavigationFixation.getChildCount() == 0) {
            if (navigation.getParent() != null)
                ((ViewGroup) navigation.getParent()).removeView(navigation);

            lineAddNavigationFixation.addView(navigation);
        }
    }
    /**
     * 状态栏高度
     * @return
     */
    private int getStatusHeight() {
        if (statusBarHeight == 0) {
            Rect rect = new Rect();
            this.getWindow().getDecorView().getWindowVisibleDisplayFrame(rect);
            return statusBarHeight = rect.top; //状态栏高度
        } else return statusBarHeight;
    }

}

MyScrollView：

import android.content.Context;
import android.util.AttributeSet;
import android.widget.ScrollView;

/**
 * author：xxf
 */
public class MyScrollView extends ScrollView {
    public ScrollChangedListener listener;

    public MyScrollView(Context context) {
        super(context);
    }

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

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


    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        if (listener != null)
            listener.onScrollChanged(l, t, oldl, oldt);
    }

    public void setListener(ScrollChangedListener listener) {
        this.listener = listener;
    }

    public static interface ScrollChangedListener {
        void onScrollChanged(int l, int t, int oldl, int oldt);
    }

}

activity_main.xm l代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <!--标题栏-->
    <TextView
        android:id="@+id/titleView"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:text="标题栏"
        android:background="#aaa"
        android:gravity="center"/>
    <!--内容布局最外层使用FrameLayout-->
    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <!--下面是自定义scrollview-->
        <com.xxfen.ceilinglayoutdemo.MyScrollView
            android:id="@+id/myScrollview"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fillViewport="true"
            android:focusable="true">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:background="@color/white"
                android:orientation="vertical">
                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="200dp"
                    android:orientation="vertical"
                    android:background="#bcc" >
                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="match_parent"
                        android:text="头部内容"
                        android:background="#bac"
                        android:gravity="center"/>
                </LinearLayout>

                <!--下面LinearLayout用于包裹导航栏控件-->
                <LinearLayout
                    android:id="@+id/lineAddNavigationFixation"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:background="@color/white"
                    android:orientation="vertical">

                   <TextView
                       android:id="@+id/navigation"
                       android:layout_width="match_parent"
                       android:layout_height="50dp"
                       android:text="导航栏"
                       android:background="#bee"
                       android:gravity="center"/>

                </LinearLayout>

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:orientation="vertical" >
                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="200dp"
                        android:orientation="vertical"
                        android:text="内容块"
                        android:gravity="center"
                        android:background="#bbe" />

                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="200dp"
                        android:orientation="vertical"
                        android:text="内容块"
                        android:gravity="center"
                        android:background="#bbe" />

                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="200dp"
                        android:orientation="vertical"
                        android:text="内容块"
                        android:gravity="center"
                        android:background="#bbe" />
                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="200dp"
                        android:orientation="vertical"
                        android:text="内容块"
                        android:gravity="center"
                        android:background="#bbe" />

                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="200dp"
                        android:orientation="vertical"
                        android:text="内容块"
                        android:gravity="center"
                        android:background="#bbe" />
                </LinearLayout>


            </LinearLayout>

        </com.xxfen.ceilinglayoutdemo.MyScrollView>
        <!--下面LinearLayout用于占位-->
        <LinearLayout
            android:id="@+id/lineAddNavigationSuspension"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@color/white"
            android:orientation="vertical">

        </LinearLayout>
    </FrameLayout>

</LinearLayout>

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