java - 使用 RecyclerView GridLayoutManager 通过 ItemDecoration 制作列间距时 Item 宽度不一样

标签 java android android-recyclerview gridlayoutmanager

我正在尝试使用 RecyclerView 和 GridLayoutManager 来制作 3 列网格，我现在使用 ItemDecoration 来制作列间距问题是第三列中项目的宽度小于第一列和第二列中的项目!请参阅下面的屏幕截图。

enter image description here

如果我不将自定义的ItemDecoration添加到RecyclerView，一切正常。

这是我的代码:

MainActivity.java:

public class MainActivity extends AppCompatActivity {

    private RecyclerView mRecyclerView;
    private MyAdapter mAdapter;

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

        mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
        mAdapter = new MyAdapter();
        mRecyclerView.setAdapter(mAdapter);

        GridLayoutManager gridLayoutManager = new GridLayoutManager(this, 3);
        mRecyclerView.setLayoutManager(gridLayoutManager);

        int horizontalSpacing = 20;
        int verticalSpacing = 10;
        SpacingDecoration decoration = new SpacingDecoration(horizontalSpacing, verticalSpacing, true);
        mRecyclerView.addItemDecoration(decoration);
    }


    private static class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

        private int[] mColors = new int[]{Color.RED, Color.BLUE, Color.MAGENTA};

        private static class ItemHolder extends RecyclerView.ViewHolder {

            public MyTextView title;

            public ItemHolder(View itemView) {
                super(itemView);
                title = (MyTextView) itemView.findViewById(android.R.id.text1);
                title.setTextColor(Color.WHITE);
            }
        }

        @Override
        public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false);
            ItemHolder holder = new ItemHolder(itemView);
            holder.itemView.setOnClickListener(itemClickListener);
            return holder;
        }

        @Override
        public void onBindViewHolder(RecyclerView.ViewHolder rHolder, int position) {
            ItemHolder holder = (ItemHolder) rHolder;

            holder.title.setText(String.format("[%d]width:%d", position, holder.itemView.getWidth()));
            holder.itemView.setBackgroundColor(mColors[position % mColors.length]);
            holder.itemView.setTag(position);
            holder.title.setTag(position);
        }

        @Override
        public int getItemCount() {
            return 50;
        }

        private View.OnClickListener itemClickListener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = (int) v.getTag();
                showText(v.getContext(), String.format("[%d]->width:%d", position, v.getWidth()));
            }
        };

    }

    public static class SpacingDecoration extends RecyclerView.ItemDecoration {

        private int mHorizontalSpacing = 5;
        private int mVerticalSpacing = 5;
        private boolean isSetMargin = true;

        public SpacingDecoration(int hSpacing, int vSpacing, boolean setMargin) {
            isSetMargin = setMargin;
            mHorizontalSpacing = hSpacing;
            mVerticalSpacing = vSpacing;
        }

        @Override
        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
            boolean isSetMarginLeftAndRight = this.isSetMargin;
            int bottomOffset = mVerticalSpacing;
            int leftOffset = 0;
            int rightOffset = 0;

            RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams) view.getLayoutParams();
            if (parent.getLayoutManager() instanceof GridLayoutManager) {
                GridLayoutManager lm = (GridLayoutManager) parent.getLayoutManager();
                GridLayoutManager.LayoutParams gridLp = (GridLayoutManager.LayoutParams) lp;

                if (gridLp.getSpanSize() == lm.getSpanCount()) {
                    // Current item is occupied the whole row
                    // We just need to care about margin left and right now
                    if (isSetMarginLeftAndRight) {
                        leftOffset = mHorizontalSpacing;
                        rightOffset = mHorizontalSpacing;
                    }
                } else {
                    // Current item isn't occupied the whole row
                    if (gridLp.getSpanIndex() > 0) {
                        // Set space between items in one row
                        leftOffset = mHorizontalSpacing;
                    } else if (gridLp.getSpanIndex() == 0 && isSetMarginLeftAndRight) {
                        // Set left margin of a row
                        leftOffset = mHorizontalSpacing;
                    }
                    if (gridLp.getSpanIndex() == lm.getSpanCount() - gridLp.getSpanSize() && isSetMarginLeftAndRight) {
                        // Set right margin of a row
                        rightOffset = mHorizontalSpacing;
                    }
                }
            }
            outRect.set(leftOffset, 0, rightOffset, bottomOffset);
        }
    }


    private static Toast sToast;

    public static void showText(Context context, String text) {
        if (sToast != null) {
            sToast.cancel();
        }
        sToast = Toast.makeText(context, text, Toast.LENGTH_LONG);
        sToast.show();
    }
}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent">

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

</RelativeLayout>

item.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">

    <com.example.liuqing.rvgldemo.MyTextView
        android:id="@android:id/text1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="5dp"
        android:textColor="#ffffff"
        android:textAppearance="?android:attr/textAppearanceMedium"/>
</LinearLayout>

MyTextView.java

public class MyTextView extends TextView {

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

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

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

    @Override
    public void onWindowFocusChanged(boolean hasWindowFocus) {
        super.onWindowFocusChanged(hasWindowFocus);
        if (hasWindowFocus) {
            setText("[" + getTag() + "]width:" + getWidth());
        }
    }
}

如果有人能解释这个问题，将不胜感激。

最佳答案

我自己找到了问题的原因。 ItemDecoration 中的偏移量被视为元素尺寸(宽度和高度)的一部分!

让我们看一下上面问题中的示例代码和屏幕截图。屏幕截图的宽度是 480 像素，这里是 3 列，每个项目的宽度是 480/3 = 160 像素。在 SpacingDecoration 中，我在第一列和第二列添加了一个左偏移量(20 像素)，因此第一列和第二列项的内容宽度为 160-20=140，然后我将左右都添加在第 3 列 item 上的偏移量，所以第 3 列 item 的内容宽度为 160-20-20=120。

现在我们想让每个item的内容(彩色矩形)的宽度一样，我们必须计算每列item占一行总间距的多少，但是我懒得写详分割析，所以我在这里写一个粗略的计算过程，你可以通过并直接得出结论。

spacing = 20
columnCount = 3
rowWidth = 480
itemWidth = rowWidth / columnCount
itemOccupiedSpacing = (spacing * (columnCount + 1)) / columnCount = spacing + spacing * (1/columnCount)
itemContentWidth = itemWidth - itemOccupiedSpacing

firstItemLeftOffset = spacing = spacing * (3/columnCount)
firstItemRightOffset = itemOccupiedSpacing - spacing = spacing * (1/columnCount)
secondItemLeftOffset = spacing - firstRightOffset = spacing * (2/columnCount)
secondItemRightOffset = itemOccupiedSpacing - secondLeftOffset = spacing * (2/columnCount)
thirdItemLeftOffset = itemOccupiedSpacing - secondLeftOffset = spacing * (1/columnCount)
thirdItemRightOffset = spacing = spacing * (3/columnCount)

我们可以得出结论:

itemLeftOffset = spacing * ((columnCount - colunmnIndex) / columnCount)
itemRightOffset = spacing * ((colunmnIndex + 1) / columnCount)

colummnIndex 大于 0 且小于 columnCount。

这是我自定义的 ItemDecoration 间距，它适用于 LinearLayoutManager、GridLayoutManager 和 StaggeredGridLayoutManager，所有项目的宽度相同。您可以直接在代码中使用它。

public class SpacingDecoration extends ItemDecoration {

    private int mHorizontalSpacing = 0;
    private int mVerticalSpacing = 0;
    private boolean mIncludeEdge = false;

    public SpacingDecoration(int hSpacing, int vSpacing, boolean includeEdge) {
        mHorizontalSpacing = hSpacing;
        mVerticalSpacing = vSpacing;
        mIncludeEdge = includeEdge;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        // Only handle the vertical situation
        int position = parent.getChildAdapterPosition(view);
        if (parent.getLayoutManager() instanceof GridLayoutManager) {
            GridLayoutManager layoutManager = (GridLayoutManager) parent.getLayoutManager();
            int spanCount = layoutManager.getSpanCount();
            int column = position % spanCount;
            getGridItemOffsets(outRect, position, column, spanCount);
        } else if (parent.getLayoutManager() instanceof StaggeredGridLayoutManager) {
            StaggeredGridLayoutManager layoutManager = (StaggeredGridLayoutManager) parent.getLayoutManager();
            int spanCount = layoutManager.getSpanCount();
            StaggeredGridLayoutManager.LayoutParams lp = (StaggeredGridLayoutManager.LayoutParams) view.getLayoutParams();
            int column = lp.getSpanIndex();
            getGridItemOffsets(outRect, position, column, spanCount);
        } else if (parent.getLayoutManager() instanceof LinearLayoutManager) {
            outRect.left = mHorizontalSpacing;
            outRect.right = mHorizontalSpacing;
            if (mIncludeEdge) {
                if (position == 0) {
                    outRect.top = mVerticalSpacing;
                }
                outRect.bottom = mVerticalSpacing;
            } else {
                if (position > 0) {
                    outRect.top = mVerticalSpacing;
                }
            }
        }
    }

    private void getGridItemOffsets(Rect outRect, int position, int column, int spanCount) {
        if (mIncludeEdge) {
            outRect.left = mHorizontalSpacing * (spanCount - column) / spanCount;
            outRect.right = mHorizontalSpacing * (column + 1) / spanCount;
            if (position < spanCount) {
                outRect.top = mVerticalSpacing;
            }
            outRect.bottom = mVerticalSpacing;
        } else {
            outRect.left = mHorizontalSpacing * column / spanCount;
            outRect.right = mHorizontalSpacing * (spanCount - 1 - column) / spanCount;
            if (position >= spanCount) {
                outRect.top = mVerticalSpacing;
            }
        }
    }
}

关于java - 使用 RecyclerView GridLayoutManager 通过 ItemDecoration 制作列间距时 Item 宽度不一样，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30524599/

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