Android从0到1实现流布局控件-轻识

流布局在在项目中还是会时不时地用到的，比如在搜索历史记录，分类，热门词语等可用标签来显示的，都可以设计成流布局的展示方式。这里我从0到1实现了一个搜索历史记录的流布局。

演示效果：

实现步骤：

1、创建FlowLayoutView，创建数据源，并添加各个子view。

2、在onMeasure方法中遍历子view，通过简单计算剩余宽度，用集合存储当前行的几个子view，再根据子view的累加高度设置自己的最终尺寸。

3、在onLayout方法中，遍历每一行，遍历该行的子view，依次调动layout设置子view位置。

核心点：

引入行的概念，每一行存储自己应该放置的子view。判断该行剩余空间和该子view的宽度，来决定能放入该行，还是需要新建下一行来存储。

主要代码：

/** * description 流布局viewGroup */public class FlowLayoutView extends ViewGroup {    private List<Row> rows = new ArrayList<>();    private int usedWidth;    /**     * 当前需要操作的行     */    private Row curRow;    private int verticalPadding = 30;    private int horizontalPadding = 40;
    public FlowLayoutView(Context context) {        super(context);    }
    public FlowLayoutView(Context context, AttributeSet attrs) {        super(context, attrs);    }
    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        restoreLine();  //每次重新布局，属性要初始化，避免onMeasure重复调用混乱问题
        //子view设置宽高为父view大小减去padding值        int width = MeasureSpec.getSize(widthMeasureSpec);        int height = MeasureSpec.getSize(heightMeasureSpec);        int widthMode = MeasureSpec.getMode(widthMeasureSpec);        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        //设置每个子view宽高，并且将每个子View归到自己的行        for (int i = 0; i < getChildCount(); i++) {            View childView = getChildAt(i);
            //设置子view设置AT_MOST模式，即布局属性为wrap_content            int childWidthSpec = MeasureSpec.makeMeasureSpec(width, widthMode == MeasureSpec.EXACTLY ? MeasureSpec.AT_MOST : widthMode);            int childHeightSpec = MeasureSpec.makeMeasureSpec(height, heightMode == MeasureSpec.EXACTLY ? MeasureSpec.AT_MOST : heightMode);            childView.measure(childWidthSpec, childHeightSpec);
            if (curRow == null) {                curRow = new Row();            }
            //根据当前childview宽度和剩余宽度判断是否能放进当前行，放不了就要换行            if (childView.getMeasuredWidth() + horizontalPadding > width - usedWidth) {                //先换行，再放入                nextLine();            }
            usedWidth += childView.getMeasuredWidth() + horizontalPadding;            curRow.addView(childView);        }
        //将最后一个row加入到rows中        rows.add(curRow);
        //根据子view组成的高度重设自己高度        int finalHeight = 0;        for (Row row : rows) {            finalHeight += row.height + verticalPadding;        }
        setMeasuredDimension(width, finalHeight);    }
    @Override    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int top = 0;        //遍历每一行，将每一行子view布局        for (Row row : rows) {            row.layout(top);            top = top + row.height + verticalPadding;        }    }
    /**     * 换行，需要将当前row存储，并且创建新的row，新的行使用空间置0     */    private void nextLine() {        rows.add(curRow);        curRow = new Row();        usedWidth = 0;    }
    /**     * 每次onmeasure需要重置信息     */    private void restoreLine() {        rows.clear();        curRow = new Row();        usedWidth = 0;    }
    /**     * 用于记录每一行放置子View的信息     */    class Row {        /**         * 该行放置的子view         */        private List<View> childViews = new ArrayList<>();        private int height;
        public void addView(View view) {            childViews.add(view);            height = view.getMeasuredHeight() > height ? view.getMeasuredHeight() : height;  //高度取最高子view的高度        }
        public int getSize() {            return childViews.size();        }
        /**         * 将当前childViews进行布局         * top 当前hang处于的顶部高度         */        public void layout(int top) {            int leftMargin = 0;            for (int i = 0; i < childViews.size(); i++) {                View view = childViews.get(i);                view.layout(leftMargin, top, leftMargin + view.getMeasuredWidth(), top + view.getMeasuredHeight());                leftMargin = leftMargin + view.getMeasuredWidth() + horizontalPadding;            }        }    }}

MainActivity代码：

public class MainActivity extends AppCompatActivity {    private FlowLayoutView flowLayoutView;
    private String[] tagTextArray = new String[]{"天猫精灵", "充电台灯", "睡衣", "手表", "创意水杯", "夏天T恤男", "灯光机械键盘",            "计算机原理", "学霸笔记本", "可口可乐", "跑步机", "旅行箱", "竹浆卫生纸", "吹风机", "洗面奶", "窗帘"};
    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);
        init();    }
    private void init() {        flowLayoutView = findViewById(R.id.flowlayout);
        TextView tvAddTag = findViewById(R.id.tv_addtag);        tvAddTag.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                View view = LayoutInflater.from(getApplicationContext()).inflate(R.layout.item_tagview, null);                TextView tvContent = view.findViewById(R.id.tv_content);                tvContent.setText(tagTextArray[(int) (Math.random()*tagTextArray.length)]);                flowLayoutView.addView(view);            }        });    }}

源码地址：

https://github.com/18380438200/FlowLayoutView

到这里就结束啦。