问题：

滚动时获取RecycleView的中心可见项

尹弘壮

2023-03-14

这就是我想要的：

如上图所示，我想在RecycleView上画一条中心线，然后在滚动时获得中心项（以及向左或向右移动）
以下是我尝试画一个水平的RecycleView：

    HorizontalAdapter adapter = new HorizontalAdapter(data);
    LinearLayoutManager layoutManager
            = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
    recycleView.setLayoutManager(layoutManager);
    recycleView.setAdapter(adapter);

有没有办法知道哪个项目移动到了回收视图的中心？如何将RecycleView向左或向右滚动一个位置？

更新：我尝试使用滚动侦听器来获得中间位置，但它不能作为一个方面。

  @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            int firstPos = layoutManager.findFirstVisibleItemPosition();
            int lastPos = layoutManager.findLastVisibleItemPosition();
            int middle = Math.abs(lastPos - firstPos) / 2 + firstPos;

            int selectedPos = -1;
            for (int i = 0; i < adapter.getItemCount(); i++) {
                if (i == middle) {
                    adapter.getItem(i).setSelected(true);
                    selectedPos = i;
                } else {
                    adapter.getItem(i).setSelected(false);
                }
            }

            adapter.notifyDataSetChanged();
        }

并得到结果：

我只想在蓝色Rect上更改选中的项目（使文本变为白色）

共有3个答案

韩瀚

2023-03-14

哦，孩子。我寻找这个答案已经快一个星期了，然后找到了解决办法。自定义布局管理器？否。ItemDecorator？不。

以下是最简单的方法：

<android.support.v7.widget.RecyclerView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:paddingStart="150dp"
    android:paddingEnd="150dp"
    android:clipToPadding="false" />

关键部分是：

    android:paddingStart="150dp"
    android:paddingEnd="150dp"
    android:clipToPadding="false"

然后只需将SnapHelper分配给您的RecylcerView：

val snapHelper = LinearSnapHelper()
snapHelper.attachToRecyclerView(recyclerView)

就是这样。这个问题最简单、最完美的解决方案

符学

2023-03-14

有时需要将整个示例代码块放在一起，因为可能会遗漏一些内容。这是我所拥有的，请随意纠正任何事情，因为我可能在某个地方犯了一些小错误。是的，这个答案是@tranhieu答案的扩展。谢谢@tranhieu。

主要活动。JAVA

package com.test;

import android.app.Activity;
import android.graphics.Color;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.TextView;

import java.util.ArrayList;

public class MainActivity extends Activity {

    private static final String TAG = MainActivity.class.getSimpleName();

    public float firstItemWidthDate;
    public float paddingDate;
    public float itemWidthDate;
    public int allPixelsDate;
    public int finalWidthDate;
    private DateAdapter dateAdapter;
    private ArrayList<LabelerDate> labelerDates = new ArrayList<>();

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getRecyclerviewDate();

    }


    public void getRecyclerviewDate() {
        final RecyclerView recyclerViewDate = (RecyclerView) findViewById(R.id.rv_tasks_date);
        if (recyclerViewDate != null) {
            recyclerViewDate.postDelayed(new Runnable() {
                @Override
                public void run() {
                    setDateValue();
                }
            }, 300);
            recyclerViewDate.postDelayed(new Runnable() {
                @Override
                public void run() {
                    recyclerViewDate.smoothScrollToPosition(dateAdapter.getItemCount()-1);
                    setDateValue();
                }
            }, 5000);
        }
        ViewTreeObserver vtoDate = recyclerViewDate.getViewTreeObserver();
        vtoDate.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {


            @Override
            public boolean onPreDraw() {
                recyclerViewDate.getViewTreeObserver().removeOnPreDrawListener(this);
                finalWidthDate = recyclerViewDate.getMeasuredWidth();
                itemWidthDate = getResources().getDimension(R.dimen.item_dob_width);
                paddingDate = (finalWidthDate - itemWidthDate) / 2;
                firstItemWidthDate = paddingDate;
                allPixelsDate = 0;

                final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
                dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
                recyclerViewDate.setLayoutManager(dateLayoutManager);
                recyclerViewDate.addOnScrollListener(new RecyclerView.OnScrollListener() {
                    @Override
                    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                        super.onScrollStateChanged(recyclerView, newState);
                        synchronized (this) {
                            if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                                calculatePositionAndScrollDate(recyclerView);
                            }
                        }

                    }

                    @Override
                    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                        super.onScrolled(recyclerView, dx, dy);
                        allPixelsDate += dx;
                    }
                });
                if (labelerDates == null) {
                    labelerDates = new ArrayList<>();
                }
                genLabelerDate();
                dateAdapter = new DateAdapter(labelerDates, (int) firstItemWidthDate);
                recyclerViewDate.setAdapter(dateAdapter);
                dateAdapter.setSelecteditem(dateAdapter.getItemCount() - 1);
                return true;
            }
        });
    }

    private void genLabelerDate() {
        for (int i = 0; i < 32; i++) {
            LabelerDate labelerDate = new LabelerDate();
            labelerDate.setNumber(Integer.toString(i));
            labelerDates.add(labelerDate);

            if (i == 0 || i == 31) {
                labelerDate.setType(DateAdapter.VIEW_TYPE_PADDING);
            } else {
                labelerDate.setType(DateAdapter.VIEW_TYPE_ITEM);
            }
        }
    }
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/

    private void calculatePositionAndScrollDate(RecyclerView recyclerView) {
        int expectedPositionDate = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);

        if (expectedPositionDate == -1) {
            expectedPositionDate = 0;
        } else if (expectedPositionDate >= recyclerView.getAdapter().getItemCount() - 2) {
            expectedPositionDate--;
        }
        scrollListToPositionDate(recyclerView, expectedPositionDate);

    }

    /* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
    private void scrollListToPositionDate(RecyclerView recyclerView, int expectedPositionDate) {
        float targetScrollPosDate = expectedPositionDate * itemWidthDate + firstItemWidthDate - paddingDate;
        float missingPxDate = targetScrollPosDate - allPixelsDate;
        if (missingPxDate != 0) {
            recyclerView.smoothScrollBy((int) missingPxDate, 0);
        }
        setDateValue();
    }

    //
    private void setDateValue() {
        int expectedPositionDateColor = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
        int setColorDate = expectedPositionDateColor + 1;
//        set color here
        dateAdapter.setSelecteditem(setColorDate);
    }


    public class DateAdapter extends RecyclerView.Adapter<DateAdapter.DateViewHolder> {
        private ArrayList<LabelerDate> dateDataList;


        private static final int VIEW_TYPE_PADDING = 1;
        private static final int VIEW_TYPE_ITEM = 2;
        private int paddingWidthDate = 0;

        private int selectedItem = -1;

        public DateAdapter(ArrayList<LabelerDate> dateData, int paddingWidthDate) {
            this.dateDataList = dateData;
            this.paddingWidthDate = paddingWidthDate;

        }


        @Override
        public DateViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            if (viewType == VIEW_TYPE_ITEM) {
                final View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item,
                    parent, false);
                return new DateViewHolder(view);
            } else {
                View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item,
                    parent, false);

                RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
                layoutParams.width = paddingWidthDate;
                view.setLayoutParams(layoutParams);
                return new DateViewHolder(view);
            }
        }

        @Override
        public void onBindViewHolder(DateViewHolder holder, int position) {
            LabelerDate labelerDate = dateDataList.get(position);
            if (getItemViewType(position) == VIEW_TYPE_ITEM) {
                holder.tvDate.setText(labelerDate.getNumber());
                holder.tvDate.setVisibility(View.VISIBLE);

                Log.d(TAG, "default " + position + ", selected " + selectedItem);
                if (position == selectedItem) {
                    Log.d(TAG, "center" + position);
                    holder.tvDate.setTextColor(Color.parseColor("#76FF03"));
                    holder.tvDate.setTextSize(35);

                } else {
                    holder.tvDate.setTextColor(Color.WHITE);
                    holder.tvDate.setTextSize(18);
                }
            } else {
                holder.tvDate.setVisibility(View.INVISIBLE);
            }
        }

        public void setSelecteditem(int selecteditem) {
            this.selectedItem = selecteditem;
            notifyDataSetChanged();
        }

        @Override
        public int getItemCount() {
            return dateDataList.size();
        }

        @Override
        public int getItemViewType(int position) {
            LabelerDate labelerDate = dateDataList.get(position);
            if (labelerDate.getType() == VIEW_TYPE_PADDING) {
                return VIEW_TYPE_PADDING;
            } else {
                return VIEW_TYPE_ITEM;
            }

        }


        public class DateViewHolder extends RecyclerView.ViewHolder {
            public TextView tvDate;

            public DateViewHolder(View itemView) {
                super(itemView);
                tvDate = (TextView) itemView.findViewById(R.id.txt_date);
            }
        }
    }

    private class LabelerDate {
        private int type;
        private String number;

        public String getNumber() {
            return number;
        }

        public void setNumber(String number) {
            this.number = number;
        }

        public int getType() {
            return type;
        }

        public void setType(int type) {
            this.type = type;
        }
    }
}

主要活动。xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.RecyclerView
            android:id="@+id/rv_tasks_date"
            android:layout_width="match_parent"
            android:layout_height="48dp" />

        <ImageView
            android:layout_width="48dp"
            android:layout_height="48dp"
            android:layout_gravity="center"
            android:layout_marginTop="48dp"
            android:src="@android:drawable/ic_dialog_info" />
    </FrameLayout>

</LinearLayout>

项目xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical" android:layout_width="wrap_content"
              android:layout_height="match_parent">

    <TextView
        android:id="@+id/txt_date"
        android:layout_width="@dimen/item_dob_width"
        android:layout_height="48dp"
        android:text="32"
        android:textColor="@android:color/white"
        android:background="@android:color/darker_gray"
        android:textSize="28sp"
        android:gravity="center"/>

</LinearLayout>

dimens.xml

<resources>
    <dimen name="item_dob_width">100dp</dimen>
</resources>

郎恺

2023-03-14

这是我的回收查看适配器

public class DateAdapter extends RecyclerView.Adapter<DateAdapter.DateViewHolder> {
private ArrayList<LabelerDate> dateDataList;


private static final int VIEW_TYPE_PADDING = 1;
private static final int VIEW_TYPE_ITEM = 2;
private int paddingWidthDate = 0;

private int selectedItem = -1;

public DateAdapter(ArrayList<LabelerDate> dateData, int paddingWidthDate) {
    this.dateDataList = dateData;
    this.paddingWidthDate = paddingWidthDate;

}


@Override
public DateViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == VIEW_TYPE_ITEM) {
        final View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_date,
                parent, false);
        return new DateViewHolder(view);
    } else {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_padding,
                parent, false);

        RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) view.getLayoutParams();
        layoutParams.width = paddingWidthDate;
        view.setLayoutParams(layoutParams);
        return new DateViewHolder(view);
    }
}

@Override
public void onBindViewHolder(DateViewHolder holder, int position) {
    LabelerDate labelerDate = dateDataList.get(position);
    if (getItemViewType(position) == VIEW_TYPE_ITEM) {
        if(labelerDate.dateType.equals(BirthDayActivity.DateType.C31))
                holder.tvDate.setText(String.valueOf(labelerDate.valueDate));
                holder.tvDate.setVisibility(View.VISIBLE);
                holder.imgSmall.setVisibility(View.VISIBLE);

        if (position == selectedItem) {
            holder.tvDate.setTextColor(Color.parseColor("#094673"));
            holder.tvDate.setTextSize(35);
            holder.imgSmall.setBackgroundResource(R.color.textviewbold);

        } else {
            holder.tvDate.setTextColor(Color.GRAY);
            holder.tvDate.setTextSize(35);
            holder.imgSmall.setBackgroundResource(R.color.gray);
        }
    }
}

public void setSelecteditem(int selecteditem) {
    this.selectedItem = selecteditem;
    notifyDataSetChanged();
}

@Override
public int getItemCount() {
    return dateDataList.size();
}

@Override
public int getItemViewType(int position) {
    LabelerDate labelerDate = dateDataList.get(position);
    if (labelerDate.dateType.equals(BirthDayActivity.DateType.NONE)) {
        return VIEW_TYPE_PADDING;
    }
    return VIEW_TYPE_ITEM;
}


public class DateViewHolder extends RecyclerView.ViewHolder {
    public TextView tvDate;
    public ImageView imgSmall;

    public DateViewHolder(View itemView) {
        super(itemView);
        tvDate = (TextView) itemView.findViewById(R.id.tvNumberDate);
        imgSmall = (ImageView) itemView.findViewById(R.id.small_marked_dob);
    }
}}

这是最重要的alogrithm：

public void getRecyclerviewDate() {
    recyclerViewDate = (RecyclerView) findViewById(R.id.recyclerViewDay);
    ViewTreeObserver vtoDate = recyclerViewDate.getViewTreeObserver();
    vtoDate.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
        @Override
        public boolean onPreDraw() {
            recyclerViewDate.getViewTreeObserver().removeOnPreDrawListener(this);
            finalWidthDate = recyclerViewDate.getMeasuredWidth();
            itemWidthDate = getResources().getDimension(R.dimen.item_dob_width);
            paddingDate = (finalWidthDate - itemWidthDate) / 2;
            firstItemWidthDate = paddingDate ;
            allPixelsDate = 0;

            final LinearLayoutManager dateLayoutManager = new LinearLayoutManager(getApplicationContext());
            dateLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
            recyclerViewDate.setLayoutManager(dateLayoutManager);
            recyclerViewDate.addOnScrollListener(new RecyclerView.OnScrollListener() {
                @Override
                public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                    super.onScrollStateChanged(recyclerView, newState);
                    synchronized (this) {
                         if(newState == RecyclerView.SCROLL_STATE_IDLE){           
                            calculatePositionAndScrollDate(recyclerView);
                        }
                    }

                }

                @Override
                public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                    super.onScrolled(recyclerView, dx, dy);
                    allPixelsDate += dx;
                }
            });
            if (labelerDates == null)
                labelerDates = new ArrayList<>();
            labelerDates.addAll(genLabelerDate(currentMonth, currentYear));
            dateAdapter = new DateAdapter(labelerDates, (int) firstItemWidthDate);
            recyclerViewDate.setAdapter(dateAdapter);
            return true;
        }
    });
}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/

private void calculatePositionAndScrollDate(RecyclerView recyclerView) {
    int expectedPositionDate = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);

    if (expectedPositionDate == -1) {
        expectedPositionDate = 0;
    } else if (expectedPositionDate >= recyclerView.getAdapter().getItemCount() - 2) {
        expectedPositionDate--;
    }
    scrollListToPositionDate(recyclerView, expectedPositionDate);

}
/* this if most important, if expectedPositionDate < 0 recyclerView will return to nearest item*/
private void scrollListToPositionDate(RecyclerView recyclerView, int expectedPositionDate) {
    float targetScrollPosDate = expectedPositionDate * itemWidthDate + firstItemWidthDate - paddingDate;
    float missingPxDate = targetScrollPosDate - allPixelsDate;
    if (missingPxDate != 0) {
        recyclerView.smoothScrollBy((int) missingPxDate, 0);
    }
}
private void setDateValue() {
    int expectedPositionDateColor = Math.round((allPixelsDate + paddingDate - firstItemWidthDate) / itemWidthDate);
    setColorDate = expectedPositionDateColor + 1;
    //set color here
    dateAdapter.setSelecteditem(setColorDate);
}
 @Override
protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);   
    allPixelsDate = savedInstanceState.getFloat(BUNDLE_LIST_PIXELS_DATE);
    allPixelsDateChanged = savedInstanceState.getFloat(BUNDLE_LIST_PIXELS_DATE_CHANGED);
}

@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putFloat(BUNDLE_LIST_PIXELS_DATE, allPixelsDate);
    outState.putFloat(BUNDLE_LIST_PIXELS_DATE_CHANGED, allPixelsDateChanged);
}

看这个视频链接，这是我的应用程序演示

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共有3个答案

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