通过前面的
Android Glide 3.7.0 源码解析 (二) , 从一次图片加载流程看源码
我们知道
Request(真实) 只有在图片组件的大小准备好了才会开始真正的加载
public void begin() {
startTime = LogTime.getLogTime();
if (model == null) {
onException(null);
return;
status = Status.WAITING_FOR_SIZE;
if (Util.isValidDimensions(overrideWidth, overrideHeight)) {
onSizeReady(overrideWidth, overrideHeight);
} else {
target.getSize(this);
if (!isComplete() && !isFailed() && canNotifyStatusChanged()) {
target.onLoadStarted(getPlaceholderDrawable());
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logV("finished run method in " + LogTime.getElapsedMillis(startTime));
我们参考 Android Glide 3.7.0 源码解析 (二) , 从一次图片加载流程看源码 一文中介绍的流程, 可得 target 是一个 GlideDrawableImageViewTarget 类型, 下面就来看看是如何获取 size 的
如何获取 size
private final SizeDeterminer sizeDeterminer;
@Override
public void getSize(SizeReadyCallback cb) {
sizeDeterminer.getSize(cb);
public void getSize(SizeReadyCallback cb) {
int currentWidth = getViewWidthOrParam();
int currentHeight = getViewHeightOrParam();
if (isSizeValid(currentWidth) && isSizeValid(currentHeight)) {
cb.onSizeReady(currentWidth, currentHeight);
} else {
if (!cbs.contains(cb)) {
cbs.add(cb);
if (layoutListener == null) {
final ViewTreeObserver observer = view.getViewTreeObserver();
layoutListener = new SizeDeterminerLayoutListener(this);
observer.addOnPreDrawListener(layoutListener);
private boolean isSizeValid(int size) {
return size > 0 || size == LayoutParams.WRAP_CONTENT;
关于 isSizeValid >0 有效可以理解, 为啥 size == LayoutParams.WRAP_CONTENT 也会被判定有效???
其实在分析完后, 发现这条判断条件好像也用不上
需要弄清楚两个问题:
getViewWidthOrParam() 和 getViewHeightOrParam() 方法是如何计算宽高的
SizeDeterminerLayoutListener 监听 View 的变化之后, 又做了些啥
计算Size的基本函数
我们来看看如何计算 当前状态下(可能没加载完全) 的View的宽高
private static final int PENDING_SIZE = 0;
private int getViewHeightOrParam() {
final LayoutParams layoutParams = view.getLayoutParams();
if (isSizeValid(view.getHeight())) {
return view.getHeight();
} else if (layoutParams != null) {
return getSizeForParam(layoutParams.height, true );
} else {
return PENDING_SIZE;
private int getViewWidthOrParam() {
final LayoutParams layoutParams = view.getLayoutParams();
if (isSizeValid(view.getWidth())) {
return view.getWidth();
} else if (layoutParams != null) {
return getSizeForParam(layoutParams.width, false );
} else {
return PENDING_SIZE;
private int getSizeForParam(int param, boolean isHeight) {
if (param == LayoutParams.WRAP_CONTENT) {
Point displayDimens = getDisplayDimens();
return isHeight ? displayDimens.y : displayDimens.x;
} else {
return param;
private Point getDisplayDimens() {
if (displayDimens != null) {
return displayDimens;
WindowManager windowManager = (WindowManager) view.getContext().getSystemService(Context.WINDOW_SERVICE);
Display display = windowManager.getDefaultDisplay();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
displayDimens = new Point();
display.getSize(displayDimens);
} else {
displayDimens = new Point(display.getWidth(), display.getHeight());
return displayDimens;
至此, 我们看完了计算 View 大小的函数 ( getViewWidthOrParam() / getViewHeightOrParam() ) , 原理很简单
getHeight / getWidth 能计算出来 >0 的值, 就以它为准
LayoutParams.WRAP_CONTENT 或者 LayoutParams.MATCH_PARENT 时, windowManager.getDefaultDisplay() 来获得 View 的显示区域
简单画了一个流程图
3. 一种是返回 0 或者 MATCH_PARENT , 表示我没计算出来
4. 一种是返回 getHeight / getWidth 或者 windowManager.getDefaultDisplay() , 表示我计算出来了
分析完基本的计算宽高的函数, 我们再来看看, SizeDeterminerLayoutListener 监听 View 刷新之后都做了啥
监听 View 刷新
private static class SizeDeterminerLayoutListener implements ViewTreeObserver.OnPreDrawListener {
private final WeakReference<SizeDeterminer> sizeDeterminerRef;
public SizeDeterminerLayoutListener(SizeDeterminer sizeDeterminer) {
sizeDeterminerRef = new WeakReference<SizeDeterminer>(sizeDeterminer);
@Override
public boolean onPreDraw() {
SizeDeterminer sizeDeterminer = sizeDeterminerRef.get();
if (sizeDeterminer != null) {
sizeDeterminer.checkCurrentDimens();
return true;
private void checkCurrentDimens() {
if (cbs.isEmpty()) {
return;
int currentWidth = getViewWidthOrParam();
int currentHeight = getViewHeightOrParam();
if (!isSizeValid(currentWidth) || !isSizeValid(currentHeight)) {
return;
notifyCbs(currentWidth, currentHeight);
ViewTreeObserver observer = view.getViewTreeObserver();
if (observer.isAlive()) {
observer.removeOnPreDrawListener(layoutListener);
layoutListener = null;
private void notifyCbs(int width, int height) {
for (SizeReadyCallback cb : cbs) {
cb.onSizeReady(width, height);
cbs.clear();
逻辑很简单
View 刷新了
再次计算宽高, 有效 -> GenericRequest.onSizeReady
() 开始加载图片; 移除刷新监听
再次计算宽高, 无效 -> 啥也不做, 继续傻等
说了那么多, 总结一下流程
- 31.3w
-
baldwin
React.js
GitHub
- 8.3w
-
Android帅次
Android
Google
