Android 自定义流式布局

前言

自定义布局FlowLayout实现了界面的流式布局，子控件水平排列，直到排满后换行显示。
FlowLayout需要继承ViewGroup类，覆盖onMeasure(int, int)和onLayout(boolean, int, int, int, int)的方法。

1. 自定义LayoutParams

为了控制子控件的布局，自定义LayoutParams类，设置对齐方式。

public static class LayoutParams extends ViewGroup.LayoutParams {
    public static final int GRAVITY_TOP         = 0;
    public static final int GRAVITY_MIDDLE      = 1;
    public static final int GRAVITY_BOTTOM      = 2;

    int gravity = GRAVITY_TOP;

    public LayoutParams(Context c, AttributeSet attrs) {
        super(c, attrs);

        TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.FlowLayout_Layout);
        gravity = a.getInt(R.styleable.FlowLayout_Layout_gravity, GRAVITY_TOP);
        a.recycle();
    }

    public LayoutParams(int width, int height) {
        super(width, height);
    }

    public LayoutParams(ViewGroup.LayoutParams source) {
        super(source);

        if (source instanceof LayoutParams) {
            gravity = ((LayoutParams) source).gravity;
        }
    }

}

同时定义FlowLayout_Layout

在FlowLayout中添加支持LayoutParams代码。

@Override
protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
    return p != null && p instanceof LayoutParams;
}

@Override
protected LayoutParams generateDefaultLayoutParams() {
    return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
}

@Override
protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
    return new LayoutParams(p);
}

@Override
public LayoutParams generateLayoutParams(AttributeSet attrs) {
    return new LayoutParams(getContext(), attrs);
}

2. onMeasure方法

onMeasure(int, int)方法通过计算子控件的高度和宽度获取自身高度。

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int width = MeasureSpec.getSize(widthMeasureSpec);
    int height = 0;

    int count = getChildCount();
    int startX = 0;
    int childHeight = 0;

    for (int index = 0; index < count; index++) {
        View child = getChildAt(index);
        if (child.getVisibility() != View.GONE) {
            // 计算child宽高
            measureChild(child, widthMeasureSpec, heightMeasureSpec);

            // 如果超过一行，换行重新开始
            if (startX + child.getMeasuredWidth() > width) {
                height += childHeight;

                childHeight = child.getMeasuredHeight();
                startX = child.getMeasuredWidth();
            } else {
                childHeight = Math.max(childHeight, child.getMeasuredHeight());
                startX += child.getMeasuredWidth();
            }
        }
    }
    height += childHeight;

    setMeasuredDimension(widthMeasureSpec,
            MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY));
}

3. onLayout方法

onLayout(boolean, int, int, int, int)方法对子控件进行布局显示。 其中left、top、right和bottom代表在父View中的距离，宽度是right-left，高度是bottom-top。

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    int count = getChildCount();

    int startX = 0;
    int height = 0;
    int width = right - left;
    int childHeight = 0;
    int startIndex = 0;

    for (int index = 0; index < count; index++) {
        View child = getChildAt(index);
        if (child.getVisibility() != View.GONE) {

            // 如果超过一行，换行显示
            if (startX + child.getMeasuredWidth() > width) {
                if (index > startIndex) {
                    layoutChildren(height, childHeight, startIndex, index);
                }

                startIndex = index;
                height += childHeight;
                startX = child.getMeasuredWidth();
                childHeight = child.getMeasuredHeight();
            } else {
                childHeight = Math.max(childHeight, child.getMeasuredHeight());
                startX += child.getMeasuredWidth();
            }
        }
    }

    if (startIndex < count) {
        layoutChildren(height, childHeight, startIndex, count);
    }
}

private void layoutChildren(int top, int childHeight, int startIndex, int endIndex) {
    int startX = 0;

    for (int index = startIndex; index < endIndex; index++) {
        View child = getChildAt(index);
        if (child.getVisibility() != View.GONE) {
            LayoutParams lp = (LayoutParams) child.getLayoutParams();

            int offsetY = 0;
            if (lp.gravity == LayoutParams.GRAVITY_MIDDLE) {
                offsetY = (childHeight - child.getMeasuredHeight()) / 2;
            } else if (lp.gravity == LayoutParams.GRAVITY_BOTTOM) {
                offsetY = childHeight - child.getMeasuredHeight();
            }

            child.layout(startX, top + offsetY,
                    startX + child.getMeasuredWidth(),
                    top + offsetY + child.getMeasuredHeight());

            startX += child.getMeasuredWidth();
        }
    }
}

4. 布局文件

效果如下

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