Android开发之仿淘宝商品详情页

看到有人在问如何实现淘宝商品详情页效果，手痒了就撸了一个，献上效果图

大致梳理一下思路，这里不提供源码

状态栏透明使用开源库StatusBarCompat，为了兼容手机4.4

dependencies {
        compile ('com.github.niorgai:StatusBarCompat:2.1.4', {
            exclude group: 'com.android.support'
        })
    }

allprojects {
        repositories {
            ...
            maven { url "https://jitpack.io" }
        }
    }

标题栏图标透明度变化参考Api setAlpha()已过时

 icon.setImageAlpha(0);

Banner控件为ViewPager,淘宝显示为正方形，这里需要修改ViewPager measure函数

public class IdeaViewPager extends ViewPager {

    private Point point;

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

    public IdeaViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        point = new Point();
        windowManager.getDefaultDisplay().getSize(point);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        setMeasuredDimension(point.x,point.x);
    }
}

测量View高度，获取到高度集合绑定到ScrollView,根据ScrollView滑动距离判断是属于哪一个Tab选项

    public int getMeasureHeight(View view){
        int width = View.MeasureSpec.makeMeasureSpec(0,
                View.MeasureSpec.UNSPECIFIED);
        int height = View.MeasureSpec.makeMeasureSpec(0,
                View.MeasureSpec.UNSPECIFIED);
        view.measure(width, height);
        return view.getMeasuredHeight();
    }

重新onScrollChanged函数，实现ViewPager滑动速度比其他View慢

  @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        if (viewPager != null && t != oldt) {
            viewPager.setTranslationY(t/2);
        }
    }

根据限定距离（Banner）计算百分比偏移量，实现颜色渐变、透明度渐变（淘宝商品详情页有二次颜色渐变）

 @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);

        if(viewPager!=null&&t<=point.x-headerHeight&&getOnScrollChangedColorListener()!=null){

            getOnScrollChangedColorListener().onChanged(Math.abs(t)/Float.valueOf(point.x-headerHeight));
            if(t<=(point.x-headerHeight)/2){
                getOnScrollChangedColorListener().onChangedFirstColor(t/(point.x-headerHeight)/2);
            }else{
                getOnScrollChangedColorListener().onChangedSecondColor((t-(point.x-headerHeight)/2)/(point.x-headerHeight)/2);
            }

        }

        int currentPosition = getCurrentPosition(t,arrayDistance);
        if(currentPosition!=position&&getOnSelectedIndicateChangedListener()!=null){
            getOnSelectedIndicateChangedListener().onSelectedChanged(currentPosition);
        }
        this.position = currentPosition;
    }

单一颜色渐变透明度，还原argb通道，修改a值

 ideaScrollView.setOnScrollChangedColorListener(new IdeaScrollView.OnScrollChangedColorListener() {
            @Override
            public void onChanged(float percentage) {

                int color = getAlphaColor(percentage>0.9f?1.0f:percentage);
                header.setBackgroundDrawable(new ColorDrawable(color));
                radioGroup.setBackgroundDrawable(new ColorDrawable(color));
                icon.setImageAlpha((int) ((percentage>0.9f?1.0f:percentage)*255));
                radioGroup.setAlpha((percentage>0.9f?1.0f:percentage)*255);

                setRadioButtonTextColor(percentage);

            }

            @Override
            public void onChangedFirstColor(float percentage) {

            }

            @Override
            public void onChangedSecondColor(float percentage) {

            }
        });

        ideaScrollView.setOnSelectedIndicateChangedListener(new IdeaScrollView.OnSelectedIndicateChangedListener() {
            @Override
            public void onSelectedChanged(int position) {
                isNeedScrollTo = false;
                radioGroup.check(radioGroup.getChildAt(position).getId());
                isNeedScrollTo = true;
            }
        });

    public int getAlphaColor(float f){
        return Color.argb((int) (f*255),0x09,0xc1,0xf4);
    }

Tab选项属性不能太频繁，会有颜色值闪烁情况出现，这里需要策略

 public void setRadioButtonTextColor(float percentage){
        if(Math.abs(percentage-currentPercentage)>=0.1f){
            for(int i=0;i<radioGroup.getChildCount();i++){
                RadioButton radioButton = (RadioButton) radioGroup.getChildAt(i);
                radioButton.setTextColor(radioButton.isChecked()?getRadioCheckedAlphaColor(percentage):getRadioAlphaColor(percentage));
            }
            this.currentPercentage = percentage;
        }
    }

判断当前属于哪个选项，根据滑动距离与传入绑定的View高度集合来计算

private int getCurrentPosition(int t, ArrayList<Integer> arrayDistance) {

        int index = 0;
        for (int i=0;i<arrayDistance.size();i++){
            if(i==arrayDistance.size()-1){
                index = i;
            }else {
                if(t>=arrayDistance.get(i)&&t<arrayDistance.get(i+1)){
                    index = i;
                    break;
                }
            }
        }
        return index;
    }

切换选项卡以及回到顶部按钮的具体实现参考scrollTo函数

    private void scrollToPosition(int position){
        scrollTo(0,arrayDistance.get(position));
    }

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以上代码实现了上图效果，当然也可以使用RecyclerView AbsListView做容器