android自定義流式佈局解析與原始碼
今天給大家解析一下自定義流式佈局的編寫,以及分析一下寫程式碼過程遇到的難點。該佈局支援水平垂直方向和子view gravity選擇,先看一下執行的效果,左邊是垂直佈局,右邊是水平佈局,套一個scrollview就支援滑動了
說一下遇到的兩個難點:
- 自定義LayoutParams類
編寫過程中需要自定義一個LayoutParams,這個LayoutParams類是要繼承子父類的LayoutParams,在編碼過程中需要將子view的ViewGroup.LayoutParams轉成自定義的LayoutParams
LayoutParams childLayoutParams = (LayoutParams) child.getLayoutParams();
這行程式碼如果沒有進行處理就會報錯,這時候就需要重寫幾個函式
@Override
protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
return p instanceof LayoutParams;
}
@Override
protected LayoutParams generateDefaultLayoutParams() {
return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
}
@Override
public LayoutParams generateLayoutParams(AttributeSet attributeSet) {
return new LayoutParams(getContext(), attributeSet);
}
@Override
protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
return new LayoutParams(p);
}
為什麼需要重寫這幾個函式呢?我們去看看ViewGroup的原始碼就知道了
private void addViewInner(View child, int index, LayoutParams params,
boolean preventRequestLayout) {
....
//注意該params為child的LayoutParams
if (!checkLayoutParams(params)) {
params = generateLayoutParams(params);
}
....
}
在新增每個子view的時候都會先檢測該子view的params是不是該父view的LayoutParams型別,如果不是,則會呼叫generateLayoutParams函式將ViewGroup.LayoutParams型別轉換為自定義的LayoutParams型別。而generateDefaultLayoutParams函式則是子view無layoutparmas的時候生成一個預設layoutparams。複寫這四個函式之後,上面那行程式碼就不會出異常了。
- 自定義attr
<declare-styleable name="FlowLayout">
<attr name="orientation" format="enum">
<enum name="vertical" value="0"/>
<enum name="horizontal" value="1"/>
</attr>
<attr name="childGravity">
<flag name="top" value="0x30"/>
<flag name="bottom" value="0x50"/>
<flag name="left" value="0x03"/>
<flag name="right" value="0x05"/>
<flag name="center" value="0x11"/>
</attr>
<attr name="verticalSpacing" format="dimension"/>
<attr name="horizontalSpacing" format="dimension"/>
</declare-styleable>
關於gravity的使用,自己看了一下原始碼,具體瞭解了一下原理,它總共用了8位二進位制來表示,前面4位用來表示y軸,後4位用來表示x軸,具體可以看Gravity類,這個類中有兩個掩碼HORIZONTAL_GRAVITY_MASK(00000111)和VERTICAL_GRAVITY_MASK(01110000),接著如果把所有的gravity變數都用二進位制來表示,就很明瞭地知道這些變數與和或之後的結果是另外哪個gravity變數。
原始碼分析
最後就來直接看看程式碼,整個類最複雜的就是onMeasure函數了,這個函式中需要做大量的計算和處理,先貼出來程式碼:
FlowLayout.class類
public class FlowLayout extends ViewGroup{
public static final int VERTICAL = 0;
public static final int HORIZONTAL = 1;
private final int CENTER = 1;
private final int TOP = 2;
private final int BOTTOM =3;
private final int LEFT = 4;
private final int RIGHT = 5;
//預設間隙
private int verticalSpacing = 10;
private int horizontalSpacing = 10;
//佈局方向
private int orientation = HORIZONTAL;
//子view放置gravity
private int childGravity = 1;
public FlowLayout(Context context) {
this(context, null);
}
public FlowLayout(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public FlowLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
getAttrValue(attrs);
}
private void getAttrValue(AttributeSet attrs){
TypedArray typedArray = getContext().obtainStyledAttributes(attrs, R.styleable.FlowLayout);
verticalSpacing = typedArray.getDimensionPixelSize(R.styleable.FlowLayout_verticalSpacing, 10);
horizontalSpacing = typedArray.getDimensionPixelSize(R.styleable.FlowLayout_horizontalSpacing, 10);
orientation = typedArray.getInt(R.styleable.FlowLayout_orientation, HORIZONTAL);
int gravity = typedArray.getInt(R.styleable.FlowLayout_childGravity, Gravity.TOP);
if (orientation == HORIZONTAL) {
gravity = gravity & Gravity.VERTICAL_GRAVITY_MASK;
if (gravity == Gravity.TOP)
childGravity = TOP;
else if (gravity == Gravity.BOTTOM)
childGravity = BOTTOM;
else
childGravity = CENTER;
}else{
gravity = gravity & Gravity.HORIZONTAL_GRAVITY_MASK;
if (gravity == Gravity.LEFT)
childGravity = LEFT;
else if (gravity == Gravity.RIGHT)
childGravity = RIGHT;
else
childGravity = CENTER;
}
typedArray.recycle();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
if (getChildCount() <= 0){
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
return;
}
int paddingTop = getPaddingTop();
int paddingLeft = getPaddingLeft();
int paddingRight = getPaddingRight();
int paddingBottom = getPaddingBottom();
int width;
int height;
int childWidth;
int childHeight;
//該行最大子view大小
int maxChildSize = 0;
//剩餘大小
int lastSize;
//水平佈局,寬度固定,高度變化
if (orientation == HORIZONTAL) {
width = MeasureSpec.getSize(widthMeasureSpec);
height = 0;
lastSize = width - paddingLeft - paddingRight;
//如果第一個子view的大小已經超過容器大小
if (lastSize < getChildAt(0).getLayoutParams().width)
throw new ChildSizeTooLongException("the 0 child's width too long");
}
//垂直佈局,高度固定,寬度變化
else{
width = 0;
height = MeasureSpec.getSize(heightMeasureSpec);
lastSize = height - paddingTop - paddingBottom;
//如果第一個子view的大小已經超過容器大小
if (lastSize < getChildAt(0).getLayoutParams().height)
throw new ChildSizeTooLongException("the 0 child's height too long");
}
//每行的第一個item的序號
int firstItemOfLine = 0;
//x,y座標
int x = paddingLeft;
int y = paddingTop;
int childSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
LayoutParams lp = (LayoutParams) child.getLayoutParams();
childHeight = lp.height;
childWidth = lp.width;
if (childHeight <= 0 || childWidth <= 0) {
child.measure(childSpec, childSpec);
childWidth = child.getMeasuredWidth();
childHeight = child.getMeasuredHeight();
}
child.measure(MeasureSpec.makeMeasureSpec(childWidth, MeasureSpec.EXACTLY),
MeasureSpec.makeMeasureSpec(childHeight, MeasureSpec.EXACTLY));
if (orientation == HORIZONTAL) {
lastSize = lastSize - childWidth - horizontalSpacing;
}else{
lastSize = lastSize - childHeight - verticalSpacing;
}
//需要換行
if (lastSize < 0) {
if (orientation == HORIZONTAL) {
//根據gravity將上一行的子view放置在正確的位置上
for (int j=firstItemOfLine; j<i; j++){
View lineChild = getChildAt(j);
LayoutParams childLayoutParams = (LayoutParams) lineChild.getLayoutParams();
if (childGravity == TOP){
//預設,無需處理
}else if (childGravity == BOTTOM){
childLayoutParams.y += maxChildSize - lineChild.getMeasuredHeight();
}else if (childGravity == CENTER){
childLayoutParams.y += (maxChildSize - lineChild.getMeasuredHeight())/2;
}
}
//將大小重置
lastSize = width - paddingLeft - paddingRight - childWidth;
//換行之後該行的第一個view大小超過整體父view大小
if (lastSize < 0)
throw new ChildSizeTooLongException("the " + i + " child's width too long");
//高換行
height += maxChildSize + verticalSpacing;
//換行之後的第一行座標
x = paddingLeft;
y += maxChildSize + verticalSpacing;
//將最大高度值置為這第一個view的高度
maxChildSize = childHeight;
}else{
//根據gravity將上一行的子view放置在正確的位置上
for (int j=firstItemOfLine; j<i; j++){
View lineChild = getChildAt(j);
LayoutParams childLayoutParams = (LayoutParams) lineChild.getLayoutParams();
if (childGravity == LEFT){
//預設,無需處理
}else if (childGravity == RIGHT){
childLayoutParams.x += maxChildSize - lineChild.getMeasuredWidth();
}else if (childGravity == CENTER){
childLayoutParams.x += (maxChildSize - lineChild.getMeasuredWidth())/2;
}
}
//將大小重置
lastSize = height - paddingTop - paddingBottom - childHeight;
//換行之後該行的第一個view大小超過整體父view大小
if (lastSize < 0)
throw new ChildSizeTooLongException("the " + i + " child's height too long");
//寬換列
width += maxChildSize + horizontalSpacing;
//換列之後的第一列座標
x += maxChildSize + horizontalSpacing;
y = paddingTop;
//將最大寬度值置為這第一個view的寬度
maxChildSize = childWidth;
}
//換行之後的第一個item序號
firstItemOfLine= i;
}
//不需要換行
else {
if (orientation == HORIZONTAL) {
//計算出這一行子view中高度最大的view
maxChildSize = maxChildSize > childHeight ? maxChildSize : childHeight;
}else{
//計算出這一列子view中寬度最大的view
maxChildSize = maxChildSize > childWidth ? maxChildSize : childWidth;
}
}
lp.setXY(x, y);
if (orientation == HORIZONTAL) {
x += childWidth + horizontalSpacing;
}else{
y += childHeight + verticalSpacing;
}
}
if (orientation == HORIZONTAL) {
height += maxChildSize;
height += + paddingBottom + paddingTop;
heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);
//不要忘記最後一行
for (int i=firstItemOfLine; i<getChildCount(); i++){
View lineChild = getChildAt(i);
LayoutParams childLayoutParams = (LayoutParams) lineChild.getLayoutParams();
if (childGravity == TOP){
//預設,無需處理
}else if (childGravity == BOTTOM){
childLayoutParams.y += maxChildSize - lineChild.getMeasuredHeight();
}else if (childGravity == CENTER){
childLayoutParams.y += (maxChildSize - lineChild.getMeasuredHeight())/2;
}
}
}else{
width += maxChildSize;
width += paddingLeft + paddingRight;
//不要忘記最後一列
for (int i=firstItemOfLine; i<getChildCount(); i++){
View lineChild = getChildAt(i);
LayoutParams childLayoutParams = (LayoutParams) lineChild.getLayoutParams();
if (childGravity == LEFT){
//預設,無需處理
}else if (childGravity == RIGHT){
childLayoutParams.x += maxChildSize - lineChild.getMeasuredWidth();
}else if (childGravity == CENTER){
childLayoutParams.x += (maxChildSize - lineChild.getMeasuredWidth())/2;
}
}
}
setMeasuredDimension(resolveSize(width, widthMeasureSpec), resolveSize(height, heightMeasureSpec));
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
final int count = getChildCount();
for (int i = 0; i < count; i++) {
View child = getChildAt(i);
LayoutParams lp = (LayoutParams) child.getLayoutParams();
child.layout(lp.x, lp.y, lp.x + child.getMeasuredWidth(), lp.y + child.getMeasuredHeight());
}
}
/**
* 設定佈局方向
* @param orientation {@link #HORIZONTAL}or{@link #VERTICAL}
*/
public void setOrientation(int orientation){
if (orientation!=HORIZONTAL && orientation!=VERTICAL)
throw new IllegalArgumentException("orientation error");
this.orientation = orientation;
invalidate();
}
public int getOrientation(){
return orientation;
}
@Override
protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
return p instanceof LayoutParams;
}
@Override
protected LayoutParams generateDefaultLayoutParams() {
return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
}
@Override
public LayoutParams generateLayoutParams(AttributeSet attributeSet) {
return new LayoutParams(getContext(), attributeSet);
}
@Override
protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
return new LayoutParams(p);
}
public static class LayoutParams extends ViewGroup.LayoutParams{
public int x;
public int y;
public LayoutParams(ViewGroup.LayoutParams source) {
super(source);
}
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
}
public LayoutParams(int width, int height) {
super(width, height);
}
public void setXY(int x, int y){
this.x = x;
this.y = y;
}
}
public static class ChildSizeTooLongException extends RuntimeException{
public ChildSizeTooLongException(String message){
super(message);
}
}
}
onMeasure函式第一步根據佈局方向來確定整個view的寬或高,固定一個值不變,去計算另外一個值大小。第二步,迴圈該view所有子view,先獲取子view寬和高,如果未知就讓子view自己去計算寬和高;接著根據子view的大小去計算是否需要換行,垂直佈局和水平佈局的處理方式有些許差異;最後計算出子view的x和y軸座標,並且賦值到該子view的layoutparams中即可。第三步,根據以上的計算結果最後統計出整個父view的大小並且呼叫setMeasuredDimension方法收尾即可。
onLayout函式非常簡單,就是根據onMeasure函式中的計算結果x和y來佈局所有子view。
問題討論
最後還有一個問題就是
Method 'onMeasure' is too complex to analyze by data flow algorithm
由於在onMeasure函式裡面的計算和處理程式碼有點多,導致在實際onMeasure操作時有些耗時,經測算,在HTC one m8t上面加入1000個子view,onMeasure函式會執行400ms左右,在500個以上就能明顯感覺到卡頓,這個需要怎麼處理,onMeasure函式我已經優化過了,留下的都是一些必要的操作,求指點~~
整體原始碼下載
佈局類FlowLayout.class程式碼位於com.android.libcore_ui.widget.FlowLayout中
測試類FlowLayoutActivity.class程式碼位於com.android.sample.test_widget.FlowLayoutActivity中。
最後可以厚顏無恥的要一顆星麼~(@^_^@)~