BshRecyclerView

package com.unilife.fridge.home.ui.main.widget;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Rect;
import android.support.annotation.Nullable;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import android.view.WindowManager;

import com.unilife.fridge.home.R;

/**
 * Created by cj on 2018/1/4.
 */

public class BshRecyclerView extends RecyclerView {

    private static final String TAG = "cj";
    private Bitmap gradientView;
    private Bitmap gradientView2;
    private Bitmap gradientTop70;
    private Bitmap gradientBottom70;
    private int totalHeight;
    private int totalWidth;
    private boolean showTop = false;
    private boolean showBottom = false;
    private boolean isIdle = true;
    private float density;
    private Paint paint;

    public BshRecyclerView(Context context) {
        this(context, null);
    }

    public BshRecyclerView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public BshRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        Bitmap gradientView22 = BitmapFactory.decodeResource(getResources(), R.drawable.shape_shadow2);
        Bitmap gradientView11 = BitmapFactory.decodeResource(getResources(), R.drawable.shape_shadow);
        DisplayMetrics dm = new DisplayMetrics();
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        windowManager.getDefaultDisplay().getMetrics(dm);
        density = dm.density;
        Log.e(TAG, "BshRecyclerView:density: " + density);

        paint = new Paint();
        paint.setColor(Color.WHITE);


        // 创建操作图片用的matrix对象
        Matrix matrix = new Matrix();
        // 缩放图片动作
        matrix.postScale(1 / density, 1 / density);
        //原大小
        //上
        gradientView2 = Bitmap.createBitmap(gradientView22, 0, 0, gradientView22.getWidth(),
                gradientView22.getHeight(), matrix, true);

        //下
        gradientView = Bitmap.createBitmap(gradientView11, 0, 0, gradientView11.getWidth(),
                gradientView11.getHeight(), matrix, true);


        Matrix matrix70 = new Matrix();
        matrix70.postScale(0.7f, 0.7f);
        //缩小70%之后两个
        //上
        gradientTop70 = Bitmap.createBitmap(gradientView2, 0, 0, gradientView2.getWidth(),
                gradientView2.getHeight(), matrix70, true);
        //下
        gradientBottom70 = Bitmap.createBitmap(gradientView, 0, 0, gradientView.getWidth(),
                gradientView.getHeight(), matrix70, true);

        Log.e(TAG, "gradientView  width：" + gradientView.getWidth() + "  height:" + gradientView.getHeight());


        this.addOnScrollListener(new OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                    isIdle = true;
                }
                if (newState == RecyclerView.SCROLL_STATE_DRAGGING) {
                    isIdle = false;
                }
                if (newState == RecyclerView.SCROLL_STATE_SETTLING) {
                    isIdle = false;
                }
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                View child0 = recyclerView.getChildAt(0);
                int child0AdapterPosition = recyclerView.getChildAdapterPosition(child0);
                if (child0AdapterPosition != 0) {
                    showTop = true;
                } else {
                    showTop = false;
                }

                int childCount = recyclerView.getChildCount();
                View child1 = recyclerView.getChildAt(childCount - 1);
                int child1AdapterPosition = recyclerView.getChildAdapterPosition(child1);
                if (child1AdapterPosition != recyclerView.getAdapter().getItemCount() - 1) {
                    showBottom = true;
                } else {
                    showBottom = false;
                }
            }
        });
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        totalHeight = h;
        totalWidth = w;
    }

    @Override
    public void onDraw(Canvas c) {
        super.onDraw(c);

        c.drawLine(0,0,500,500,paint);

        if (showTop) {
            if (isIdle) {
                Rect rect = new Rect(0, 0, gradientView2.getWidth(), gradientView2.getHeight());
                Rect desRect = new Rect(0, 0, totalWidth, gradientView2.getHeight());
                c.drawBitmap(gradientView2, rect, desRect, null);
            } else {
                Rect rect = new Rect(0, 0, gradientTop70.getWidth(), (gradientTop70.getHeight()));
                Rect desRect = new Rect(0, 0,totalWidth, (gradientTop70.getHeight()));
                c.drawBitmap(gradientTop70, rect, desRect, null);
            }
        }

        if (showBottom) {
            if (isIdle) {
                Rect rect = new Rect(0, 0, gradientView.getWidth(), gradientView.getHeight());
                Rect desRect = new Rect(0, (int) (totalHeight - gradientView.getHeight()), totalWidth, totalHeight);
                c.drawBitmap(gradientView, rect, desRect, null);
            } else {
                Rect rect = new Rect(0, 0, gradientBottom70.getWidth(), gradientBottom70.getHeight());
                Rect desRect = new Rect(0, (int) (totalHeight - gradientBottom70.getHeight()), totalWidth, totalHeight);
                c.drawBitmap(gradientBottom70, rect, desRect, null);
            }

        }

    }
}