View背后不为人知的勾当（一）--自定义控件和测量过程
本节首先讲讲自定义控件套路，自定义属性，测量过程的问题，为了后面的几节能专注于实现特效，而不受本文这些惯用套路的影响
特效系列的目录
- 关于Draw
- 关于动画
- 关于滑动
- 关于Layout
要实现界面特效，首先得掌握：
- View的简单原理
- 自定义属性
- measure过程
- 这算是UI特效的周边技术，任何特效都得考虑这几个问题
安卓特效的实现，需要借助以下四个技术点：
- draw
- 动画
- 滑动
- layout
1 View的原理
- 原理
- 一个Activity包含一个Window对象，也就是PhoneWindow
- 在onResume()方法里，系统才会把DecoreView添加到PhoneWindow中
- DecoreView将内容显示在PhoneWindow上，所有View的监听都通过WM接收，并通过Activity回调响应的onClickListener
- DecoreView包含一个TitleView，一个ContentView，ContentView的id是android.R.id.content，所以如果你的自定义布局如SwipeBack需要将ToolBar包含在内，需要考虑把你的布局添加到DecoreView下，但国内一般不用ToolBar，而是用自己定义的TitleBar，看情况
- ContentView下才是setContentView设置的内容
- requestWindowFeature()必须在setContentView之前调用
2 自定义属性
声明和使用自定义属性：
定义attr：在values目录下，attrs.xml
<declare-styleable name="TopBar">
<attr name="title" format="string" />
<attr name="titleTextSize" format="dimension" />
<attr name="titleTextColor" format="color" />
<attr name="titleBg" format="reference|color" />
declare-styleable>
使用attr：在任意布局文件里
<xx.xx.xx.TopBar
xmlns:custom="http://schemas.android.com/apk/res-auto"
android:id="@+id/topbar"
custom:title="title"
custom:titleTextSize="15sp"
custom:titleTextColor="#aaaaaa"
custom:titleBg="@drawable/ic_launcher"
/>
处理自定义属性
取出xml中设置的属性
TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.TopBar);
mTitle = ta.getString(R.styleable.TopBar_title);
mTitleTextSize = ta.getDimension(R.styleable.TopBar_titleTextSize, 10);
mTitleTextColor = ta.getColor(R.styleable.TopBar_titleTextColor, 0);
mTitleBg = ta.getDrawable(R.styleable.TopBar_titleBg);
ta.recycle();3 measure过程
需要知道的
- View的测量过程是最复杂的，对于view来说，得考虑内容宽高的计算，对于ViewGroup来说，得考虑具体布局，padding，margin，weight等
- 可能有时需要重复measure
- MeasureSpec类：32位的int值，高2位是测量模式（最多表示4个模式），低30位是测量的大小，即宽或高的值
- 3种测量模式
- EXACTLY： 精确值
- match_parent和dp，px都相当于指定具体数值
- 特别注意一下match_parent，如果子View是match_parent, 父View是wrap_content，这里就有冲突了
- 子会被降级为AT_MOST
- AT_MOST
- wrap_content表示控件尺寸随控件内容，但不能超过父控件给的最大尺寸
- View默认是支持wrap_content的，很合理，一个空View是没有内容的
- 一般各种具体View的wrap_content会根据以下因素决定：
- 背景drawable的宽高，也就是getInstinctWidth和getInstinctHeight
- padding
- 控件内容，如TextView的内容是text，ImageView的内容是src
- minWidth和minHeight值（如果计算出的宽高小于min，则取min）
- UNSPECIFIED
- 不指定测量模式，View想多大就多大
- 这个模式也比较合理，但我也不知道能用在哪儿
- 能用在滚动控件？如果控件可以横向滚动，则传给子View的measureSpec就是不控制你宽高？
- 可能意思就是：还是wrap_content，但不限制你最大值，所以和AT_MOST有区别，这是我猜的
- EXACTLY： 精确值
如何确定测量模式：
- 首先注意：padding属性影响测量过程，margin属性影响布局过程，也影响ViewGroup的测量过程
3.1 View的默认measure行为
View默认情况下，测量过程如下：
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
//取minWidth和背景drawable的getMinimumWidth的最大值
protected int getSuggestedMinimumWidth() {
return (mBackground == null) ? mMinWidth : max(mMinWidth, mBackground.getMinimumWidth());
}
public static int getDefaultSize(int size, int measureSpec) {
int result = size;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
switch (specMode) {
case MeasureSpec.UNSPECIFIED:
result = size; //minWidth属性或者背景宽度：这个就可以认为是空白View的内容
break;
case MeasureSpec.AT_MOST: //wrap_content，此时specSize是父控件给留的最大值
case MeasureSpec.EXACTLY: //match_parent或者具体值
result = specSize;
break;
}
return result;
}
可以看出，唯一没处理的就是wrap_content的情况
3.2 一个View的测量模板
一般具体带内容的View，按下面的套路测量
* 思路也很简单
* EXACTLY：就指定我多大，那我就多大，一般这时子控件就是match_parent，或者具体数值
* AT_MOST：specSize是我的最大值，我本身也带个内容宽高，二者比较，取小的就是了，我尽量给父控件省地方
* 除非父控件放不下我了，那我就得按父控件尺寸来
* 至于calculateContentWidth和calculateContentHeight，可能会被padding，背景，内容等因素影响
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(
mearureWidth(widthMeasureSpec),
mearureHeight(heightMeasureSpec));
}
private int mearureWidth(int measureSpec){
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if(specMode == MeasureSpec.EXACTLY){
result = specSize;
}else{
result = calculateContentWidth();
if(specMode == MeasureSpec.AT_MOST){
result = Math.min(result, specSize);
}
}
return result;
}
private int mearureHeight(int measureSpec){
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if(specMode == MeasureSpec.EXACTLY){
result = specSize;
}else{
result = calculateContentHeight();
if(specMode == MeasureSpec.AT_MOST){
result = Math.min(result, specSize);
}
}
return result;
}
///你自己测量宽度：宽度wrap_content时，会走这
private int calculateContentWidth(){
return 200;
}
///你自己测量高度：宽度wrap_content时，会走这
private int calculateContentHeight(){
return 200;
}自己处理wrap_content时应注意的问题
- 内容如果是图片，文字等可测量的，则内容本身才有个尺寸，其他的如你自己画的一个圈，可能就需要你给个固定值或者自定义属性什么的了
- padding：内容宽度 + 左右padding就是测量宽度
- max和min相关属性：也会影响你最终的测量值
padding影响还挺大
- 你draw的时候，宽高是已知的，但是在这里padding也是要考虑的
3.3 ViewGroup的测量模板
模板参考：
http://www.jianshu.com/p/71e9cc942c97
http://blog.csdn.net/lmj623565791/article/details/38339817
其实ViewGroup的match_parent和固定值也好说，就是EXACTLY，主要还是wrap_content的问题
ViewGroup的onMeasure直接继承自View，所以没有实现对子控件的处理，
但是测量子控件的方法已经提供了，下面给出一个ViewGroup测量的模板
在给出模板之前，需要说明的是，关于这一节的模板和下一节的原理，不要太纠结，
一般情况下，你通过RelativeLayout或者FrameLayout的margin就可以实现任何形式的布局，
测量过程本身是很复杂的，如果不够复杂，可能你考虑的情况不够，参考LinearLayout的测量过程的代码，你就能知道为什么自己一般不要过多的干扰布局过程了
ViewGroup处理子控件的measure先不说
主要是ViewGroup在自己wrap_content时，宽高是随着子控件来的，并且和具体的布局方式还有关系，所以测量过程中计算ViewGroup自己本身宽高时，可能需要把布局算法先过一遍
模板1：不考虑子控件margin，也不考虑ViewGroup本身的wrap_content
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int count = getChildCount();
if (count > 0) {
measureChildren(widthMeasureSpec, heightMeasureSpec);
}
}
模板2：考虑margin，和考虑wrap_content
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
final int count = getChildCount();
// 临时ViewGroup大小值
int viewGroupWidth = 0;
int viewGroupHeight = 0;
if (count > 0) {
// 遍历childView
for (int i = 0; i < count; i++) {
// childView
View child = getChildAt(i);
LayoutParams lp = (LayoutParams) child.getLayoutParams();
//测量childView包含外边距
measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
// 计算父容器的期望值，下面代码我们注掉，因为这里的代码根据具体布局来
//viewGroupWidth += child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
//viewGroupHeight += child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
}
//根据子控件计算ViewGroup宽高，取决于具体布局
viewGroupWidth = calculateParentWidthBasedOnChilren();
viewGroupHeight = calculateParentHeightBasedOnChilren();
// ViewGroup内边距
viewGroupWidth += getPaddingLeft() + getPaddingRight();
viewGroupHeight += getPaddingTop() + getPaddingBottom();
//和建议最小值进行比较
viewGroupWidth = Math.max(viewGroupWidth, getSuggestedMinimumWidth());
viewGroupHeight = Math.max(viewGroupHeight, getSuggestedMinimumHeight());
}
setMeasuredDimension(resolveSize(viewGroupWidth, widthMeasureSpec), resolveSize(viewGroupHeight, heightMeasureSpec));
}
///你自己来实现，根据具体布局和子控件们的信息，算出ViewGroup的wrap_content宽度
private int calculateParentWidthBasedOnChilren(){
int viewGroupWidth = 0;
final int count = getChildCount();
for (int i = 0; i < count; i++){
View child = getChildAt(i);
LayoutParams lp = (LayoutParams) child.getLayoutParams();
//lp.leftMargin
//lp.rightMargin
//child.getMeausredWidth()
...看你怎么算了
}
return viewGroupWidth;
}
///你自己来实现，根据具体布局和子控件们的信息，算出ViewGroup的wrap_content高度
private int calculateParentHeightBasedOnChilren(){
int viewGroupHeight = 0;
final int count = getChildCount();
for (int i = 0; i < count; i++){
View child = getChildAt(i);
LayoutParams lp = (LayoutParams) child.getLayoutParams();
//lp.topMargin
//lp.bottomMargin
//child.getMeausredHeight()
...看你怎么算了
}
return viewGroupHeight;
}
以下代码是ViewGroup本身提供的
///遍历测量所有子控件
protected void measureChildren(int widthMeasureSpec, int heightMeasureSpec) {
final int size = mChildrenCount;
final View[] children = mChildren;
for (int i = 0; i < size; ++i) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) != GONE) {
//源码中是measureChild，注意还有个measureChildWithMargins
measureChild(child, widthMeasureSpec, heightMeasureSpec);
}
}
}
protected void measureChild(View child, int parentWidthMeasureSpec,
int parentHeightMeasureSpec) {
final LayoutParams lp = child.getLayoutParams();
final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
mPaddingLeft + mPaddingRight, lp.width);
final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
mPaddingTop + mPaddingBottom, lp.height);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
protected void measureChildWithMargins(View child,
int parentWidthMeasureSpec, int widthUsed,
int parentHeightMeasureSpec, int heightUsed) {
final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
+ widthUsed, lp.width);
final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin
+ heightUsed, lp.height);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
public static int resolveSize(int size, int measureSpec) {
return resolveSizeAndState(size, measureSpec, 0) & MEASURED_SIZE_MASK;
}
public static int resolveSizeAndState(int size, int measureSpec, int childMeasuredState) {
final int specMode = MeasureSpec.getMode(measureSpec);
final int specSize = MeasureSpec.getSize(measureSpec);
final int result;
switch (specMode) {
case MeasureSpec.AT_MOST:
if (specSize < size) {
result = specSize | MEASURED_STATE_TOO_SMALL;
} else {
result = size;
}
break;
case MeasureSpec.EXACTLY:
result = specSize;
break;
case MeasureSpec.UNSPECIFIED:
default:
result = size;
}
return result | (childMeasuredState & MEASURED_STATE_MASK);
}
3.4 测量过程相关源码和流程简陋分析
参考开发艺术
再看ViewGroup的测量过程
思路：
- match_parent和具体值好说
- 如果ViewGroup本身是wrap_content，那就需要根据所有子View来确定自己的宽高
- 如果一个竖直方向的LinearLayout高度是wrap_content，让你测量，你怎么测量？
- 对于每一个View，取其高度和margin
- 如果子View是wrap_content或具体数值，还好说
- 如果子View是match_parent，而咱这个LinearLayout又是个wrap_content
- 那就把子View当wrap_content来处理
- 对于每一个View，取其高度和margin
注意：
- ViewGroup提供了measureChildren, measureChildWithMargins, getChildMeasureSpec方法
- 但没有提供具体的onMeasure实现，因为也没法提供
- 再注意LinearLayout的vertical模式下，测量过程需要遍历子控件，see how tall everyone is, also remember max width
对于顶级View，即DecoreView，measure过程和普通View有点不同
private boolean measureHierarchy(final View host, final WindowManager.LayoutParams lp,
final Resources res, final int desiredWindowWidth, final int desiredWindowHeight) {
int childWidthMeasureSpec;
int childHeightMeasureSpec;
boolean windowSizeMayChange = false;
if (DEBUG_ORIENTATION || DEBUG_LAYOUT) Log.v(TAG,
"Measuring " + host + " in display " + desiredWindowWidth
+ "x" + desiredWindowHeight + "...");
boolean goodMeasure = false;
if (lp.width == ViewGroup.LayoutParams.WRAP_CONTENT) {
// On large screens, we don't want to allow dialogs to just
// stretch to fill the entire width of the screen to display
// one line of text. First try doing the layout at a smaller
// size to see if it will fit.
final DisplayMetrics packageMetrics = res.getDisplayMetrics();
res.getValue(com.android.internal.R.dimen.config_prefDialogWidth, mTmpValue, true);
int baseSize = 0;
if (mTmpValue.type == TypedValue.TYPE_DIMENSION) {
baseSize = (int)mTmpValue.getDimension(packageMetrics);
}
if (DEBUG_DIALOG) Log.v(TAG, "Window " + mView + ": baseSize=" + baseSize);
if (baseSize != 0 && desiredWindowWidth > baseSize) {
childWidthMeasureSpec = getRootMeasureSpec(baseSize, lp.width);
childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
if (DEBUG_DIALOG) Log.v(TAG, "Window " + mView + ": measured ("
+ host.getMeasuredWidth() + "," + host.getMeasuredHeight() + ")");
if ((host.getMeasuredWidthAndState()&View.MEASURED_STATE_TOO_SMALL) == 0) {
goodMeasure = true;
} else {
// Didn't fit in that size... try expanding a bit.
baseSize = (baseSize+desiredWindowWidth)/2;
if (DEBUG_DIALOG) Log.v(TAG, "Window " + mView + ": next baseSize="
+ baseSize);
childWidthMeasureSpec = getRootMeasureSpec(baseSize, lp.width);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
if (DEBUG_DIALOG) Log.v(TAG, "Window " + mView + ": measured ("
+ host.getMeasuredWidth() + "," + host.getMeasuredHeight() + ")");
if ((host.getMeasuredWidthAndState()&View.MEASURED_STATE_TOO_SMALL) == 0) {
if (DEBUG_DIALOG) Log.v(TAG, "Good!");
goodMeasure = true;
}
}
}
}
if (!goodMeasure) {
childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);
childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
if (mWidth != host.getMeasuredWidth() || mHeight != host.getMeasuredHeight()) {
windowSizeMayChange = true;
}
}
if (DBG) {
System.out.println("======================================");
System.out.println("performTraversals -- after measure");
host.debug();
}
return windowSizeMayChange;
}
看这段
if (!goodMeasure) {
childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);
childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
if (mWidth != host.getMeasuredWidth() || mHeight != host.getMeasuredHeight()) {
windowSizeMayChange = true;
}
}
desire就是屏幕宽高
private static int getRootMeasureSpec(int windowSize, int rootDimension) {
int measureSpec;
switch (rootDimension) {
case ViewGroup.LayoutParams.MATCH_PARENT:
// Window can't resize. Force root view to be windowSize.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
break;
case ViewGroup.LayoutParams.WRAP_CONTENT:
// Window can resize. Set max size for root view.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
break;
default:
// Window wants to be an exact size. Force root view to be that size.
measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
break;
}
return measureSpec;
}
上面产生的就是DecoreView的measureSpec注意一个问题，这个也曾经出现在阿里面试题里：
父是AT_MOST时，高度其实是根据子View来，
但如果此时子是match_parent，所以子也只能是AT_MOST了
Child wants to be our size, but our size is not fixed. Constrain child to not be bigger than us.
3.5 直接从RelativeLayout或者FrameLayout写自己的布局
实战：BlockLayout
现在需要一个BlockLayout，其子控件可以是任何控件，但不论其宽度指定成什么，
每一行都必须只能放3个子控件，而高度不论指定成什么，最后显示出来的都是个正方形
并且，每一行的中间那个控件，必须距左右各10dp的margin
行与行之间，也是10dp的margin
这估计是个最简单的Layout了
CubeSdk里的BlockLayout是继承RelativeLayout，实现比较简单比较巧妙,
利用了Relativelayout子控件的margin来控制，规避了自己measuue和layout，
我们应该学习
package in.srain.cube.views.block;
import android.content.Context;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
public class BlockListView extends RelativeLayout {
public interface OnItemClickListener {
void onItemClick(View v, int position);
}
private static final int INDEX_TAG = 0x04 << 24;
private BlockListAdapter mBlockListAdapter;
private LayoutInflater mLayoutInflater;
private OnItemClickListener mOnItemClickListener;
public BlockListView(Context context) {
this(context, null, 0);
}
public BlockListView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public BlockListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mLayoutInflater = LayoutInflater.from(context);
}
public void setAdapter(BlockListAdapter adapter) {
if (adapter == null) {
throw new IllegalArgumentException("adapter should not be null");
}
mBlockListAdapter = adapter;
adapter.registerView(this);
}
@Override
protected void onDetachedFromWindow() {
super.onDetachedFromWindow();
if (null != mBlockListAdapter) {
mBlockListAdapter.registerView(null);
}
}
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
if (null != mBlockListAdapter) {
mBlockListAdapter.registerView(this);
}
}
public void setOnItemClickListener(OnItemClickListener listener) {
mOnItemClickListener = listener;
}
OnClickListener mOnClickListener = new OnClickListener() {
@Override
public void onClick(View v) {
int index = (Integer) v.getTag(INDEX_TAG);
if (null != mOnItemClickListener) {
mOnItemClickListener.onItemClick(v, index);
}
}
};
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
public void onDataListChange() {
removeAllViews();
int len = mBlockListAdapter.getCount();
int w = mBlockListAdapter.getBlockWidth();
int h = mBlockListAdapter.getBlockHeight();
int columnNum = mBlockListAdapter.getCloumnNum();
int horizontalSpacing = mBlockListAdapter.getHorizontalSpacing();
int verticalSpacing = mBlockListAdapter.getVerticalSpacing();
boolean blockDescendant = getDescendantFocusability() == ViewGroup.FOCUS_BLOCK_DESCENDANTS;
for (int i = 0; i < len; i++) {
RelativeLayout.LayoutParams lyp = new RelativeLayout.LayoutParams(w, h);
int row = i / columnNum;
int clo = i % columnNum;
int left = 0;
int top = 0;
if (clo > 0) {
left = (horizontalSpacing + w) * clo;
}
if (row > 0) {
top = (verticalSpacing + h) * row;
}
lyp.setMargins(left, top, 0, 0);
View view = mBlockListAdapter.getView(mLayoutInflater, i);
if (!blockDescendant) {
view.setOnClickListener(mOnClickListener);
}
view.setTag(INDEX_TAG, i);
addView(view, lyp);
}
requestLayout();
}
}
4 自定义控件的套路
套路：
- 继承View，通过onDraw实现效果，需要考虑支持wrap_content和padding
- 默认是不支持的wrap_content的（设为wrap，实际还是使用match_parent效果）
- 继承ViewGroup，需要合理处理measure和layout过程，得考虑padding和margin，否则这俩属性就失效了，同时处理子元素的测量和布局过程
- 这种方法要想得到一个规范的Layout是很复杂的，看LinearLayout源码就知道
- 对现有控件进行扩展，比较简单，不需要考虑wrap_cotent和padding
- 创建复合控件，比较简单，也是最常见的
- 继承View，通过onDraw实现效果，需要考虑支持wrap_content和padding
几个重要的回调和注意点
- onFinishInflate() 从xml加载组件完成
- onSizeChanged() 组件大小改变
- onAttachedToWindow
- onDetachedFromWindow 动画，handler，线程之类的，应该在这里停止
- View不可见时，也需要停止线程和动画，否则可能造成内存泄漏
- 滑动冲突需要考虑
- onMeasure
- onLayout
- onTouchEvent()
其他：
- 知道怎么自定义attr
- 自定义Drawable也是个路子
5 自定义控件入门
在这里先给出入门的例子，为后面几节做准备
5.1 CircleView：版本1
效果就是画个圆，不考虑wrap_content和padding
public class CircleView extends View{
public CircleView(Context context) {
super(context);
init();
}
public CircleView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public CircleView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
public CircleView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
init();
}
private int mColor = Color.RED;
private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
private void init(){
mPaint.setColor(mColor);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int width = getWidth();
int height = getHeight();
int radius = Math.min(width, height) / 2;
canvas.drawCircle(width/2, height/2, radius, mPaint);
}
}<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffffff"
>
<org.ayo.ui.sample.view_learn.CircleView
android:layout_width="match_parent"
android:layout_height="100dp"
android:background="#000000" />
FrameLayout>- 效果：
- 默认支持了margin，因为margin由父控件处理了
- 但不支持padding，因为没有在onDraw里考虑padding
- 也不支持wrap_content，而是当做match_parent处理
- 要解决这个问题，这个例子里，需要指定个默认宽高，例如都是200px
5.2 CircleView：版本2
添加padding支持
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
final int paddingLeft = getPaddingLeft();
final int paddingRight = getPaddingRight();
final int paddingTop = getPaddingTop();
final int paddingBottom = getPaddingBottom();
int width = getWidth() - paddingLeft - paddingRight;
int height = getHeight() - paddingTop - paddingBottom;
int radius = Math.min(width, height) / 2;
canvas.drawCircle(paddingLeft + width/2, paddingTop + height/2, radius, mPaint);
}<org.ayo.ui.sample.view_learn.CircleView
android:layout_width="wrap_content"
android:layout_height="100dp"
android:layout_margin="20dp"
android:padding="20dp"
android:background="#000000" />5.3 CircleView：版本3
添加wrap_content支持
//===========================================
//为了让控件支持wrap_content时，内容尺寸取200px，需要我们重写measure过程
//===========================================
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(
mearureWidth(widthMeasureSpec),
mearureHeight(heightMeasureSpec));
}
private int mearureWidth(int measureSpec){
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if(specMode == MeasureSpec.EXACTLY){
result = specSize;
}else{
result = calculateContentWidth();
if(specMode == MeasureSpec.AT_MOST){
result = Math.min(result, specSize);
}
}
return result;
}
private int mearureHeight(int measureSpec){
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if(specMode == MeasureSpec.EXACTLY){
result = specSize;
}else{
result = calculateContentHeight();
if(specMode == MeasureSpec.AT_MOST){
result = Math.min(result, specSize);
}
}
return result;
}
private int calculateContentWidth(){
return 200;
}
private int calculateContentHeight(){
return 200;
}<org.ayo.ui.sample.view_learn.CircleView2
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="20dp"
android:padding="20dp"
android:background="#000000" />其实上面这段java代码，可以简化一下，参考开发艺术
///不考虑contentSize和specSize的大小关系，不考虑minWidth和minHeight
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
if(widthSpecMode == MeasureSpec.AT_MOST && heightSpecMode == MeasureSpec.AT_MOST){
setMeasuredDimension(200, 200);
}else if(widthSpecMode == MeasureSpec.AT_MOST){
setMeasuredDimension(200, heightSize);
}else if(heightSpecMode == MeasureSpec.AT_MOST){
setMeasuredDimension(widthSize, 200);
}
}