HarmonyOS三方件开发指南(18)-Flexbox流式布局组件

目录：
1、引言
2、VideoCache使用指南
3、VideoCache开发指南
4、《HarmonyOS三方件开发指南》系列文章合集
<span class="size" style="font-size:24px">引言</span>

上一篇给大家介绍底部导航栏的组件使用及开发指南，本篇将给大家带来另一个鸿蒙三方件的是实现：Flexbox，何为Flexbox，如果对Java的Swing比较熟悉的话一定不会陌生，就是控件根据ViewGroup的宽，自动的往右添加，如果当前行剩余空间不足，则自动添加到下一行。有点所有的控件都往左飘的感觉，第一行满了，往第二行飘\~所以也叫流式布局。鸿蒙并没有提供流式布局，但是某些场合中，流式布局还是非常适合使用的，比如关键字标签，搜索热词列表等，比如下图：

这些都特别适合使用Flexbox，本篇会带领大家自己实现Flexbox，然后使用我们自己定义的Flexbox实现上面的标签效果。学会使用一个控件和学会写一个控件，我相信大家都明白，授人以鱼不如授人以渔。

接下来看下鸿蒙模拟器的实现效果，效果图如下：

图（1）默认标签状态

图（2）标签选中状态

<span class="size" style="font-size:24px">VideoCache使用指南</span>

<span class="size" style="font-size:18px">Ø 新建工程， 添加组件Har包依赖</span>

在应用模块中添加HAR，只需要将flexboxlibrary-debug.har复制到entry\libs目录下即可

<span class="size" style="font-size:18px">Ø 修改配置文件</span>

1. 在布局中添加如下代码：

`<span class="token tag"><span class="token tag"><span class="token punctuation"><</span>com.istone.flexboxlibrary.HWFlowViewGroup</span> <span class="token attr-name"><span class="token namespace">ohos:</span>id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>$+id:viewgroup<span class="token punctuation">"</span></span> <span class="token attr-name"><span class="token namespace">ohos:</span>height</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>match\_content<span class="token punctuation">"</span></span> <span class="token attr-name"><span class="token namespace">ohos:</span>width</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>match\_parent<span class="token punctuation">"</span></span> <span class="token attr-name"><span class="token namespace">ohos:</span>background\_element</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>gray<span class="token punctuation">"</span></span> <span class="token attr-name"><span class="token namespace">ohos:</span>orientation</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>vertical<span class="token punctuation">"</span></span> <span class="token punctuation">/></span></span>
    <span class="token attr-name"><span class="token namespace">ohos:</span>id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>$+id:viewgroup<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">ohos:</span>height</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>match_content<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">ohos:</span>width</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>match_parent<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">ohos:</span>background_element</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>gray<span class="token punctuation">"</span></span>
    <span class="token attr-name"><span class="token namespace">ohos:</span>orientation</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>vertical<span class="token punctuation">"</span></span>
    <span class="token punctuation">/&gt;</span></span>`

2.在代码中通过以下方式使用：

`   //mNames 是item的数据源，可以是任意需要显示的数据类型，根据实际情况去定义
parentLayout = (HWFlowViewGroup) findComponentById(ResourceTable.Id_viewgroup);
parentLayout.HWFlowViewGroup(getContext(), mNames, parentLayout);
parentLayout.setOnItemClickListener((Component view) -> {
//item点击之后的回调
    Text text = (Text)view;
    if(text.isSelected()){
        text.setTextColor(Color.BLACK);

    }else{
        text.setTextColor(Color.WHITE);
    }
});`

<span class="size" style="font-size:24px">VideoCache开发指南</span>

在上述中，已经说明Flexbox 如何在开发过程中使用，接下来简单的分析下Flexbox 实现思路

1、对于Flexbox ，需要指定的LayoutConfig，我们目前只需要能够识别margin、padding即可

2、measureChild中计算所有childView的宽度，然后根据childView的宽度，计算当前每一行的宽度

3、最后根据计算之后的宽度，对中所有的childView进行布局。

以text为例，计算每个childView 的代码如下：

`private float measureChild(Text text) {
    Paint paint = new Paint();
    paint.setTextSize(text.getTextSize());
    float childWidth = paint.measureText(text.getText());
    childWidth = childWidth + text.getPaddingLeft() + text.getPaddingRight() + text.getMarginLeft() + text.getMarginRight();
    return childWidth;
}`

初始化每行的布局，代码如下：

`private DirectionalLayout initDirtLayout() {
    DirectionalLayout childLayout = new DirectionalLayout(mContext);
    childLayout.setOrientation(Component.HORIZONTAL);
    DirectionalLayout.LayoutConfig layoutConfig = new DirectionalLayout.LayoutConfig(ComponentContainer.LayoutConfig.MATCH_PARENT, ComponentContainer.LayoutConfig.MATCH_CONTENT);
    layoutConfig.setMargins(10, 10, 10, 10);
    childLayout.setLayoutConfig(layoutConfig);
    return childLayout;
}`

获取屏幕的宽度，代码如下：

`private void getParentWidthAndHeight() {
    Optional<span class="token tag"><span class="token tag"><span class="token punctuation"><</span>Display</span><span class="token punctuation">></span></span>  display = DisplayManager.getInstance().getDefaultDisplay(mContext);
    Point pt = new Point();
    display.get().getSize(pt);
    mParentWidth = (int) pt.getPointX();
}`

动态布局：

`private void initChildViews() {
    for (int i = 0; i < mNames.length; i++) {
        Text text = new Text(mContext);
        text.setId(i);
        text.setText(mNames[i]);
        text.setTextSize(100);
        text.setSelected(false);
        text.setTextColor(Color.WHITE);
        text.setPadding(10, 10, 10, 10);
        ShapeElement background = new ShapeElement();
        background.setRgbColor(new RgbColor(205, 92, 92));
        text.setBackground(background);
        DirectionalLayout.LayoutConfig layoutConfig = new DirectionalLayout.LayoutConfig(ComponentContainer.LayoutConfig.MATCH_CONTENT, ComponentContainer.LayoutConfig.MATCH_CONTENT);
        layoutConfig.setMargins(20, 10, 20, 10);
        text.setLayoutConfig(layoutConfig);

        if (i == 0) {
            childLayout = initDirtLayout();
            mLineWidth = measureChild(text);
            childLayout.addComponent(text);
        } else {
            mLineWidth = mLineWidth + measureChild(text);
            if (mLineWidth > (mParentWidth - childLayout.getMarginLeft() - childLayout.getMarginRight())) {
                mParentLayout.addComponent(childLayout);
                childLayout = initDirtLayout();
                mLineWidth = measureChild(text);
            }
            childLayout.addComponent(text);
            if (i == mNames.length - 1) {
                mParentLayout.addComponent(childLayout);
            }
        }

        ComponentBean bean = new ComponentBean(text, false);
        list.add(bean);

        text.setClickedListener(component -> {
            text.setSelected(!text.isSelected());
            mOnItemClickListener.onItemClick(text);
        });
    }
}
`

定义接口，实现item的点击事件

`public interface OnItemClickListener {
    void onItemClick(Component view);
}

public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
    mOnItemClickListener = onItemClickListener;
}`

按照思路看下来，是不是很简单呢？我们只需要把握住如何计算childview 的宽度，以及什么情况下添加新的一行即可。

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作者：软通田可辉
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