import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Build;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import com.google.android.material.R;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.core.view.MarginLayoutParamsCompat;
/**
* Horizontally lay out children until the row is filled and then moved to the next line. Call
* {@link FlowLayout#setSingleLine(boolean)} to disable reflow and lay all children out in one line.
*
* @hide
*/
public class FlowLayout extends ViewGroup {
private static final String TAG = "FlowLayout";
private int lineSpacing;
private int itemSpacing;
private boolean singleLine;
public FlowLayout(@NonNull Context context) {
this(context, null);
}
public FlowLayout(@NonNull Context context, @Nullable AttributeSet attrs) {
this(context, attrs, 0);
}
public FlowLayout(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
singleLine = false;
loadFromAttributes(context, attrs);
}
@TargetApi(Build.VERSION_CODES.LOLLIPOP)
public FlowLayout(
@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
singleLine = false;
loadFromAttributes(context, attrs);
}
private void loadFromAttributes(@NonNull Context context, @Nullable AttributeSet attrs) {
final TypedArray array =
context.getTheme().obtainStyledAttributes(attrs, R.styleable.FlowLayout, 0, 0);
lineSpacing = array.getDimensionPixelSize(R.styleable.FlowLayout_lineSpacing, 0);
itemSpacing = array.getDimensionPixelSize(R.styleable.FlowLayout_itemSpacing, 0);
array.recycle();
}
protected int getLineSpacing() {
return lineSpacing;
}
protected void setLineSpacing(int lineSpacing) {
this.lineSpacing = lineSpacing;
}
protected int getItemSpacing() {
return itemSpacing;
}
protected void setItemSpacing(int itemSpacing) {
this.itemSpacing = itemSpacing;
}
/**
* Returns whether this chip group is single line or reflowed multiline.
*/
public boolean isSingleLine() {
return singleLine;
}
/**
* Sets whether this chip group is single line, or reflowed multiline.
*/
public void setSingleLine(boolean singleLine) {
this.singleLine = singleLine;
}
/**
* 封装了父ViewGroup传递过来的布局的期望, 每个MeasureSpec代表了一组宽度和高度的mode和size.
* 一个MeasureSpec由大小和模式组成。它有三种模式:
* 1. UNSPECIFIED(未指定)( 0 << 30)，父ViewGroup不对子View施加任何束缚，子View可以得到任意想要的大小；
* 2. EXACTLY(完全)(1 << 30)，父ViewGroup决定子View的确切大小，子View将被限定在给定的边界里而忽略它本身大小；
* 3. AT_MOST(至多)(2 << 30)，子View至多达到指定大小的值。
*
* @param widthMeasureSpec
* @param heightMeasureSpec
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//取widthMeasureSpec的低30位
final int width = MeasureSpec.getSize(widthMeasureSpec);
//取widthMeasureSpec的高2位、低30位置0的值
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
//取heightMeasureSpec的低30位
final int height = MeasureSpec.getSize(heightMeasureSpec);
//取heightMeasureSpec的高2位、低30位置0的值
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
//如果是AT_MOST或者EXACTLY, 则maxWidth为width。
final int maxWidth = widthMode == MeasureSpec.AT_MOST || widthMode == MeasureSpec.EXACTLY
? width
: Integer.MAX_VALUE;
int childLeft = 0;
int childTop = 0;
int childBottom = childTop;
int childRight = childLeft;
int maxChildRight = 0;
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
if (child.getVisibility() == View.GONE) {
continue;
}
measureChild(child, widthMeasureSpec, heightMeasureSpec);
if ((childLeft + child.getMeasuredWidth()) > maxWidth && !isSingleLine()) {
childLeft = 0;
childTop = childBottom;
}
childRight = childLeft + child.getMeasuredWidth();
childBottom = childTop + child.getMeasuredHeight();
if (childRight > maxChildRight) {
maxChildRight = childRight;
}
childLeft += child.getMeasuredWidth();
}
//根据父ViewGroup期望的mode和size, 结合当前View实际测量的大小，确定自身实际的大小。
int finalWidth = getMeasuredDimension(width, widthMode, maxChildRight);
int finalHeight = getMeasuredDimension(height, heightMode, childBottom);
//测量完所有子View后调用setMeasuredDimension设置自身大小。
setMeasuredDimension(finalWidth, finalHeight);
}
private static int getMeasuredDimension(int size, int mode, int childrenEdge) {
switch (mode) {
case MeasureSpec.EXACTLY:
return size;
case MeasureSpec.AT_MOST:
return Math.min(childrenEdge, size);
default: // UNSPECIFIED:
return childrenEdge;
}
}
/**
* 当前View的尺寸或者位置是否发生了变化, 其中left/top/right/bottom是指当前View相对于父ViewGroup的位置.
* 在onLayout()中需要调用所有子View的layout(left, top, right, bottom)方法，其中left/top/right/bottom为子View
* 相当于当前View左上角的距离, 从而为每个子View摆放合适的位置.
* @param sizeChanged
* @param left
* @param top
* @param right
* @param bottom
*/
@Override
protected void onLayout(boolean sizeChanged, int left, int top, int right, int bottom) {
if (getChildCount() == 0) {
// Do not re-layout when there are no children.
return;
}
int paddingStart = getPaddingLeft();
int paddingEnd = getPaddingRight();
int childStart = paddingStart;
int childTop = getPaddingTop();
int childBottom = childTop;
int childEnd;
final int maxChildEnd = right - left - paddingEnd;
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
if (child.getVisibility() == View.GONE) {
continue;
}
LayoutParams lp = child.getLayoutParams();
int startMargin = 0;
int endMargin = 0;
if (lp instanceof MarginLayoutParams) {
MarginLayoutParams marginLp = (MarginLayoutParams) lp;
startMargin = MarginLayoutParamsCompat.getMarginStart(marginLp);
endMargin = MarginLayoutParamsCompat.getMarginEnd(marginLp);
}
childEnd = childStart + startMargin + child.getMeasuredWidth();
if (!singleLine && (childEnd > maxChildEnd)) {
childStart = paddingStart;
childTop = childBottom;
}
childEnd = childStart + startMargin + child.getMeasuredWidth();
childBottom = childTop + child.getMeasuredHeight();
child.layout(childStart + startMargin, childTop, childEnd, childBottom);
//更新childStart供下次使用
childStart += (startMargin + endMargin + child.getMeasuredWidth());
}
}
}
Android自定义布局FlowLayout的实现