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百度程序员开发避坑指南（移动端篇）
01
NSTimer造成的内存泄漏问题？
1.1 什么是内存泄漏？
一个对象在引用计数变为0时，系统会回收内存。如果一个本应该被回收的内存，没有被回收（引用计数>0），那么就会造成内存泄漏。
以下代码将造成内存泄漏：
@interface ViewController ()@property (nonatomic, strong) NSTimer *timer;@end
@implementation ViewController
- (void)viewDidLoad { [super viewDidLoad]; self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerTest) userInfo:nil repeats:YES];}
- (void)timerTest{ NSLog(@"%s", __func__);}
// 该ViewController将不会释放- (void)dealloc{ NSLog(@"%s", __func__); [self.timer invalidate];}1.2 分析如下：
// 伪代码@interface NSTimer ()@property (strong, nonatomic) id target;@end
// 强引用该对象self.target = target1.3 如何解决？
按照分析，那应该打破ViewController和NSTimer双方的强引用。使用弱引用（弱引用不增加对象的引用计数）。
方案1
- (void)viewDidLoad { [super viewDidLoad]; __weak typedef(self) weakSelf = self; self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) { [weakSelf timerTest]; }];}方案2
// 代理类@interface Proxy : NSObject+ (instancetype)proxyWithTarget:(id)target;// 弱引用target@property (weak, nonatomic) id target;@end
@implementation Proxy+ (instancetype)proxyWithTarget:(id)target { Proxy *proxy = [[MJProxy1 alloc] init]; proxy.target = target; return proxy;}- (id)forwardingTargetForSelector:(SEL)aSelector { return self.target;}@end
@interface ViewController ()@property (nonatomic, strong) NSTimer *timer;@end
@implementation ViewController
- (void)viewDidLoad { [super viewDidLoad]; self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:[Proxy proxyWithTarget：self] selector:@selector(timerTest) userInfo:nil repeats:YES];}
- (void)timerTest{ NSLog(@"%s", __func__);}
// 该ViewController将不会释放- (void)dealloc{ NSLog(@"%s", __func__); [self.timer invalidate];}2.1 Android焦点概念
2.2 焦点处理
2.2.1 获取焦点
private boolean requestFocusNoSearch(int direction, Rect previouslyFocusedRect) { // need to be focusable if (!canTakeFocus()) { return false; } // need to be focusable in touch mode if in touch mode if (isInTouchMode() && (FOCUSABLE_IN_TOUCH_MODE != (mViewFlags & FOCUSABLE_IN_TOUCH_MODE))) { return false; } // need to not have any parents blocking us if (hasAncestorThatBlocksDescendantFocus()) { return false; } if (!isLayoutValid()) { mPrivateFlags |= PFLAG_WANTS_FOCUS; } else { clearParentsWantFocus(); } handleFocusGainInternal(direction, previouslyFocusedRect); return true; }并不是所有View都可以获取焦点。获取焦点的前提是视图必需要有获取焦点的资格。
2.2.3 分发焦点
FOCUS_BLOCK_DESCENDANTS：This view will block any of its descendants from getting focus, even if they are focusable. FOCUS_BEFORE_DESCENDANTS：This view will get focus before any of its descendants. FOCUS_AFTER_DESCENDANTS：This view will get focus only if none of its descendants want it.
public boolean requestFocus(int direction, Rect previouslyFocusedRect) { // ...省略 int descendantFocusability = getDescendantFocusability(); boolean result; switch (descendantFocusability) { case FOCUS_BLOCK_DESCENDANTS: result = super.requestFocus(direction, previouslyFocusedRect); break; case FOCUS_BEFORE_DESCENDANTS: { final boolean took = super.requestFocus(direction, previouslyFocusedRect); result = took ? took : onRequestFocusInDescendants(direction, previouslyFocusedRect); break; } case FOCUS_AFTER_DESCENDANTS: { final boolean took = onRequestFocusInDescendants(direction, previouslyFocusedRect); result = took ? took : super.requestFocus(direction, previouslyFocusedRect); break; } default: // ...省略 } if (result && !isLayoutValid() && ((mPrivateFlags & PFLAG_WANTS_FOCUS) == 0)) { mPrivateFlags |= PFLAG_WANTS_FOCUS; } return result; }一个窗口内最多只有一个View具有焦点，或者无焦点。上述在递归分发焦点时，当有View获取焦点后则会退出递归。
根View没有焦点不能说明子View一定没有焦点。子View具有焦点，根View能够感知。
2.2.4 清除焦点
/** * Clears focus from the view, optionally propagating the change up through * the parent hierarchy and requesting that the root view place new focus. * * @param propagate whether to propagate the change up through the parent * hierarchy * @param refocus when propagate is true, specifies whether to request the * root view place new focus */ void clearFocusInternal(View focused, boolean propagate, boolean refocus) { if ((mPrivateFlags & PFLAG_FOCUSED) != 0) { mPrivateFlags &= ~PFLAG_FOCUSED; clearParentsWantFocus(); if (propagate && mParent != null) { mParent.clearChildFocus(this); } onFocusChanged(false, 0, null); refreshDrawableState(); if (propagate && (!refocus || !rootViewRequestFocus())) { notifyGlobalFocusCleared(this); } } }问题1：错误启用获取焦点能力导致点击失效
public boolean onTouchEvent(MotionEvent event) { // ...省略 switch (action) { case MotionEvent.ACTION_UP: // ...省略 // take focus if we don't have it already and we should in // touch mode. boolean focusTaken = false; if (isFocusable() && isFocusableInTouchMode() && !isFocused()) { focusTaken = requestFocus(); } // ...省略 if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) { // Only perform take click actions if we were in the pressed state if (!focusTaken) { // Use a Runnable and post this rather than calling // performClick directly. This lets other visual state // of the view update before click actions start. if (mPerformClick == null) { mPerformClick = new PerformClick(); } if (!post(mPerformClick)) { performClickInternal(); } } } } }问题2：clearFocus“无效”？
void unFocus(View focused) { clearFocusInternal(focused, false, false); }boolean rootViewRequestFocus() { final View root = getRootView(); return root != null && root.requestFocus(); } private void initViewGroup() { // ...省略 setDescendantFocusability(FOCUS_BEFORE_DESCENDANTS); // ...省略 }问题3：焦点抢占
2.3 总结
3.1 首先什么是Cookie：
Cookie是服务器保存在浏览器的一小段文本信息，每个 Cookie 的大小一般不能超过4KB。浏览器每次向服务器发出请求，就会自动附上这段信息。
3.2 Webview的Cookie存储：
3.3 Cookie属性：
Set-Cookie: TEST=1234567890; Expires=Wed, 21 Oct 2022 07:28:00 GMT; Domain=baidu.com; Path=/test;Secure; HttpOnly2.4 Cookie的设置
CookieManager.getInstance().setCookie(url, cookie); CookieManager.getInstance().getCookie(url);2.5 Cookie在请求中携带：
2.5.1 Request的Header:
// 简单写了个意思，具体实现需要遍历拼接等判断，大家明白就好CookieManager cookieManager = CookieManager.getInstance();String webviewCookies = cookieManager.getCookie(url);httpURLConnection.setRequestProperty("Cookie", webviewCookies);2.5.2 Response的Set-Header：
// 简单写了个意思，具体实现需要添加安全性的判断，大家明白就好Map> responseHeaderMap = httpURLConnection.getHeaderFields();List cookieList = responseHeaderMap.get("Set-Cookie");CookieSyncManager.createInstance(context);CookieManager cookieManager = CookieManager.getInstance();cookieManager.setAcceptCookie(true);for (String cookie : cookieList) { List httpCookieList = HttpCookie.parse(cookie); HttpCookie httpCookie = httpCookieList.get(0); String relCookie = buildCookie(httpCookie.getDomain(), httpCookie.getName(), httpCookie.getValue(), System.currentTimeMillis() + httpCookie.getMaxAge() * 1000, httpCookie.getSecure()); cookieManager.setCookie(domain, relCookie);}