Android中的线性布局LinearLayout，只能横向或纵向排列子控件，而且横向排列时不能自动换行。实际上，通过扩展ViewGroup就能够实现控件自动的往右添加，如果当前行剩余空间不足，则自动添加到下一行，也就是所谓的流式布局，上代码
自定义CustomViewGroup.java如下
public class CustomViewGroup extends ViewGroup {
int mCellWidth;
int mCellHeight;
public CustomViewGroup(Context context, AttributeSet attrs) {
super(context, attrs);
mCellWidth = 120;
mCellHeight = 120;
}
public CustomViewGroup(Context context) {
super(context);
}
public void setCellWidth(int width) {
mCellWidth = width;
requestLayout();
}
public void setCellHeight(int height) {
mCellHeight = height;
requestLayout();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int cellWidthSpec = MeasureSpec.makeMeasureSpec(mCellWidth,
MeasureSpec.AT_MOST);
int cellHeightSpec = MeasureSpec.makeMeasureSpec(mCellHeight,
MeasureSpec.AT_MOST);
int count = getChildCount();
for (int i = 0; i < count; i++) {
View childView = getChildAt(i);
measureChild(childView, cellWidthSpec, cellHeightSpec);
// childView.measure(cellWidthSpec, cellHeightSpec);
}
// 使用父容器给我们的尺寸和计算出的尺寸进行比较，选择正确的尺寸设置容器控件所占区域大小
setMeasuredDimension(resolveSize(mCellWidth * count, widthMeasureSpec),
resolveSize(mCellHeight * count, heightMeasureSpec));
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int cellWidth = mCellWidth;
int cellHeight = mCellHeight;
int columns = (r - l) / cellWidth;
if (columns < 0) {
columns = 1;
}
int x = 0;// 横坐标
int y = 0;// 纵坐标
int i = 0;
int count = getChildCount();
for (int index = 0; index < count; index++) {
final View childView = getChildAt(index);
int cWidth = childView.getMeasuredWidth(); // childView的宽度
int cHeight = childView.getMeasuredHeight();
int left = x + ((cellWidth - cWidth) / 2);// 相对父容器，左边的位置
int top = y + ((cellHeight - cHeight) / 2);
childView.layout(left, top, left + cWidth, top + cHeight);
if (i >= (columns - 1)) {
// 转到下一行
i = 0;
x = 0;
y += cellHeight;
} else {
i++;
x += cellWidth;
}
}
}
}
在xml布局中使用CustomViewGroup
<?xml version="1.0" encoding="utf-8"?>
<com.example.view.CustomViewGroup xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res/com.example.activity"
android:id="@+id/viewgroup_main_flow"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_launcher" />
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_launcher" />
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_launcher" />
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_launcher" />
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_launcher" />
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_launcher" />
</com.example.view.CustomViewGroup>
效果如下：
因为在创建CustomViewGroup时，系统会调用构造函数初始化
public CustomViewGroup(Context context, AttributeSet attrs) {
super(context, attrs);
mCellWidth = 120;
mCellHeight = 120;
}
因此所有子控件的单元格都设置为120，当然也可以通过代码改变控件大小，如下：
CustomViewGroup customViewGroup=(CustomViewGroup) findViewById(R.id.viewgroup_main_flow);
customViewGroup.setCellWidth(200);
customViewGroup.setCellHeight(200);
这个例子的效果很像GridView，但又有些不同，这只是简单的实现，我们还可以更加完善一下它。虽然这样，这个例子也有很大的局限性——那就是每个控件的大小都是一样的，如果我们的子控件不相同怎么办？
直接盗用鸿洋大神的劳动成果了，看代码
CustomViewGroup.java如下
public class CustomViewGroup extends ViewGroup {
public CustomViewGroup(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected ViewGroup.LayoutParams generateLayoutParams(
ViewGroup.LayoutParams p) {
return new MarginLayoutParams(p);
}
@Override
public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) {
return new MarginLayoutParams(getContext(), attrs);
}
@Override
protected ViewGroup.LayoutParams generateDefaultLayoutParams() {
return new MarginLayoutParams(LayoutParams.MATCH_PARENT,
LayoutParams.MATCH_PARENT);
}
/**
* 负责设置子控件的测量模式和大小,根据所有子控件设置自己的宽和高
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
// 获得ViewGroup的父容器为它设置的测量模式和大小
int sizeWidth = MeasureSpec.getSize(widthMeasureSpec);
int sizeHeight = MeasureSpec.getSize(heightMeasureSpec);
int modeWidth = MeasureSpec.getMode(widthMeasureSpec);
int modeHeight = MeasureSpec.getMode(heightMeasureSpec);
// 如果是warp_content，记录宽和高
int width = 0;
int height = 0;
/**
* 记录每一行的宽度，width取lineWidth最大宽度
*/
int lineWidth = 0;
/**
* 每一行的高度，累加至height
*/
int lineHeight = 0;
int count = getChildCount();
// 遍历每个子元素
for (int i = 0; i < count; i++) {
View childView = getChildAt(i);
// 测量每一个child的宽和高
measureChild(childView, widthMeasureSpec, heightMeasureSpec);
// 得到childView的lp
MarginLayoutParams lp = (MarginLayoutParams) childView
.getLayoutParams();
// 当前子空间实际占据的宽度
int childWidth = childView.getMeasuredWidth() + lp.leftMargin
+ lp.rightMargin;
// 当前子空间实际占据的高度
int childHeight = childView.getMeasuredHeight() + lp.topMargin
+ lp.bottomMargin;
/**
* 如果加入当前childView，则超出最大宽度，则得到目前最大宽度给width，类加height 然后开启新的一行
*/
if (lineWidth + childWidth > sizeWidth) {
width = Math.max(lineWidth, childWidth);// 取最大的
lineWidth = childWidth; // 重新开启新行，开始记录
// 叠加当前高度，
height += lineHeight;
// 开启记录下一行的高度
lineHeight = childHeight;
} else
// 否则累加值lineWidth,lineHeight取最大高度
{
lineWidth += childWidth;
lineHeight = Math.max(lineHeight, childHeight);
}
// 如果是最后一个，则将当前记录的最大宽度和当前lineWidth做比较
if (i == count - 1) {
width = Math.max(width, lineWidth);
height += lineHeight;
}
}
setMeasuredDimension((modeWidth == MeasureSpec.EXACTLY) ? sizeWidth
: width, (modeHeight == MeasureSpec.EXACTLY) ? sizeHeight
: height);
}
/**
* 存储所有的View，按行记录
*/
private List<List<View>> mAllViews = new ArrayList<List<View>>();
/**
* 记录每一行的最大高度
*/
private List<Integer> mLineHeight = new ArrayList<Integer>();
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
mAllViews.clear();
mLineHeight.clear();
int width = getWidth();
int lineWidth = 0;
int lineHeight = 0;
// 存储每一行所有的childView
List<View> lineViews = new ArrayList<View>();
int count = getChildCount();
// 遍历所有的孩子
for (int i = 0; i < count; i++) {
View childView = getChildAt(i);
MarginLayoutParams lp = (MarginLayoutParams) childView
.getLayoutParams();
int childWidth = childView.getMeasuredWidth();
int childHeight = childView.getMeasuredHeight();
// 如果已经需要换行
if (childWidth + lp.leftMargin + lp.rightMargin + lineWidth > width) {
// 记录这一行所有的View以及最大高度
mLineHeight.add(lineHeight);
// 将当前行的childView保存，然后开启新的ArrayList保存下一行的childView
mAllViews.add(lineViews);
lineWidth = 0;// 重置行宽
lineViews = new ArrayList<View>();
}
/**
* 如果不需要换行，则累加
*/
lineWidth += childWidth + lp.leftMargin + lp.rightMargin;
lineHeight = Math.max(lineHeight, childHeight + lp.topMargin
+ lp.bottomMargin);
lineViews.add(childView);
}
// 记录最后一行
mLineHeight.add(lineHeight);
mAllViews.add(lineViews);
int left = 0;
int top = 0;
// 得到总行数
int lineNums = mAllViews.size();
for (int i = 0; i < lineNums; i++) {
// 每一行的所有的views
lineViews = mAllViews.get(i);
// 当前行的最大高度
lineHeight = mLineHeight.get(i);
// 遍历当前行所有的View
for (int j = 0; j < lineViews.size(); j++) {
View child = lineViews.get(j);
if (child.getVisibility() == View.GONE) {
continue;
}
MarginLayoutParams lp = (MarginLayoutParams) child
.getLayoutParams();
// 计算childView的left,top,right,bottom
int lc = left + lp.leftMargin;
int tc = top + lp.topMargin;
int rc = lc + child.getMeasuredWidth();
int bc = tc + child.getMeasuredHeight();
child.layout(lc, tc, rc, bc);
left += child.getMeasuredWidth() + lp.rightMargin
+ lp.leftMargin;
}
left = 0;
top += lineHeight;
}
}
}
在onMeasure方法中首先得到父容器传入的测量模式和宽高值，然后遍历所有的childView，使用measureChild方法对所有的childView进行测 量。然后根据所有childView测量得出的宽和高得到该ViewGroup如果设置为wrap_content时的宽和高。最后根据模式，如果是 MeasureSpec.EXACTLY则直接使用父ViewGroup传入的宽和高，否则设置为自己计算的宽和高。然后在onLayout中完成对所有childView的布局。
看下activity_main.xml
<com.example.view.CustomViewGroup xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="200dp"
android:layout_height="wrap_content" >
<TextView
style="@style/text_style"
android:background="@drawable/flag_01"
android:text="Welcome" />
<TextView
style="@style/text_style"
android:background="@drawable/flag_01"
android:text="You" />
<TextView
style="@style/text_style"
android:background="@drawable/flag_02"
android:text="自定义" />
<TextView
style="@style/text_style"
android:background="@drawable/flag_02"
android:text="ViewGroup" />
<TextView
style="@style/text_style"
android:background="@drawable/flag_03"
android:text="努力" />
<TextView
style="@style/text_style"
android:background="@drawable/flag_03"
android:text="学习" />
<TextView
style="@style/text_style"
android:background="@drawable/flag_04"
android:text="Try you best" />
</com.example.view.CustomViewGroup>
实现效果如下：
篇幅有限，先说这么多吧
