RecyclerView实现列表上下渐变过渡效果

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由于最近项目需要,需要实现列表上下渐变过渡的效果.网上查阅了相关资料,有一种方法是实现了上方的渐变,但几乎查到的都是类似的上方渐变效果,因此,我写了下面的过渡效果,方便大家开发使用.

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Shader;
import android.support.annotation.Nullable;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;

public class FadingRecyclerView extends RecyclerView {

    private static final String TAG = "FadingRecyclerView";
    private Paint paint;
    private int height;
    private int width;
    private int spanPixel = 100;

    public FadingRecyclerView(Context context) {
        super(context);
        init(context, null);
    }

    public FadingRecyclerView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }

    public FadingRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context, attrs);
    }

    private void init(Context context, AttributeSet attrs) {
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
//      paint.setShader(new LinearGradient(0, 0, 0, 890/2, 0x00000000, 0xff000000, Shader.TileMode.CLAMP)); //仅上部渐变
    }

    public void setSpanPixel(int spanPixel) {
        this.spanPixel = spanPixel;
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        height = h;
        width = w;
        float spanFactor = spanPixel / (height / 2f);
        LinearGradient linearGradient = new LinearGradient(0, 0, 0, height / 2,
                new int[]{0x00000000, 0xff000000, 0xff000000}, new float[]{0, spanFactor, 1f}, Shader.TileMode.MIRROR);
        paint.setShader(linearGradient);
    }

    @Override
    public void draw(Canvas c) {
        c.saveLayer(0, 0, width, height, null, Canvas.ALL_SAVE_FLAG);
        super.draw(c);
        c.drawRect(0, 0, width, height, paint);
        c.restore();
    }
}

效果示意图: