Tuesday, July 21, 2015

onDraw() and onDrawOver() of ItemDecoration for RecyclerView


In the exercise of "Implement custom ItemDecoration for RecyclerView" we already implement our ItemDecoration to draw lines on items in RecyclerView, in onDraw() method. Further work on last exercise "set SpanSizeLookup to GridLayoutManager of RecyclerView", here we do more:
- draw Border on canvas of whole RecyclerView, in onDraw()
- draw a enlarged bitmap on low-right corner of RecyclerView, in onDrawOver()


com.example.androidrecyclerview.MyItemDecoration.java
package com.example.androidrecyclerview;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.support.v7.widget.RecyclerView;
import android.view.View;

public class MyItemDecoration extends RecyclerView.ItemDecoration{

    private Paint paintBlue, paintRed, paintBorder;
    private int offset;

    Bitmap bitmap;
    int bitmap_w, bitmap_h;
    Rect rectSrc;

    public MyItemDecoration(Context c){
        offset = 10;
        paintBlue = new Paint(Paint.ANTI_ALIAS_FLAG);
        paintBlue.setColor(Color.BLUE);
        paintBlue.setStyle(Paint.Style.STROKE);
        paintBlue.setStrokeWidth(3);

        paintRed = new Paint(Paint.ANTI_ALIAS_FLAG);
        paintRed.setColor(Color.RED);
        paintRed.setStyle(Paint.Style.STROKE);
        paintRed.setStrokeWidth(1);

        paintBorder = new Paint(Paint.ANTI_ALIAS_FLAG);
        paintBorder.setColor(Color.GREEN);
        paintBorder.setStyle(Paint.Style.STROKE);
        paintBorder.setStrokeWidth(10);

        bitmap = BitmapFactory.decodeResource(
                c.getResources(),
                android.R.drawable.ic_menu_info_details);
        bitmap_w = bitmap.getWidth();
        bitmap_h = bitmap.getHeight();
        rectSrc = new Rect(0, 0, bitmap_w, bitmap_h);
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        outRect.set(offset, offset, offset, offset);
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);

        final RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();

        c.drawRect(
                0,
                0,
                c.getWidth(),
                c.getHeight(),
                paintBorder);

        for(int i=0; i<parent.getChildCount(); i++){
            final View child = parent.getChildAt(i);
            c.drawRect(
                    layoutManager.getDecoratedLeft(child),
                    layoutManager.getDecoratedTop(child),
                    layoutManager.getDecoratedRight(child),
                    layoutManager.getDecoratedBottom(child),
                    paintBlue);
            c.drawRect(
                    layoutManager.getDecoratedLeft(child) + offset,
                    layoutManager.getDecoratedTop(child) + offset,
                    layoutManager.getDecoratedRight(child) - offset,
                    layoutManager.getDecoratedBottom(child) - offset,
                    paintRed);

        }

    }

    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
        c.drawBitmap(bitmap,
                rectSrc,
                new Rect(
                        c.getWidth()-(2*bitmap_w),
                        c.getHeight()-(2*bitmap_h),
                        c.getWidth(),
                        c.getHeight()),
                null);
    }
}


Have to modify constructor call of MyItemDecoration in MainActivity.java, such that we can get Resources drawable in MyItemDecoration.

        myRecyclerView.addItemDecoration(new MyItemDecoration());
to:
        myRecyclerView.addItemDecoration(new MyItemDecoration(this));

download filesDownload the files (Android Studio Format).

Next:
Android example using RecyclerView with CardView


- More step-by-step examples of RecyclerView.

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