Android View的22500行源码分析系列（一）setFlag 方法，setVisibilty,setFoucus,setEnable等方法内部实现

一直想系统地学习Android源码，最近又计划写一个自定义控件系列的博客，而在自定义控件的过程中，许多技巧和方法需要你在Android View，ViewGroup的源码中得到灵感。因此，这一个View的22500行源码分析系列就诞生了

，本系列基于api23的View的源码，主要是对源码的注解作一些翻译和简单的总结，目的是让大家了解整个View的工

作流程，一些主要方法实现里面的细节问题。说时迟那时快，老司机开车啦，赶紧上车

首先我们看一下View常用的几个方法：

@RemotableViewMethod
public void setVisibility(@Visibility int visibility) {
    setFlags(visibility, VISIBILITY_MASK);
}      

public void setFocusable(boolean focusable) {
    if (!focusable) {
        setFlags(0, FOCUSABLE_IN_TOUCH_MODE);
    }
    setFlags(focusable ? FOCUSABLE : NOT_FOCUSABLE, FOCUSABLE_MASK);
}
      
    
public void setEnabled(boolean enabled) {
    if (enabled == isEnabled()) return;

    setFlags(enabled ? ENABLED : DISABLED, ENABLED_MASK);

    /*
     * The View most likely has to change its appearance, so refresh
     * the drawable state.      
    
视图大多数可能改变它的样子，所以刷新drawable的状态
     */
    refreshDrawableState();

    // Invalidate too, since the default behavior for views is to be
    // be drawn at 50% alpha rather than to change the drawable.      
    
//同时也要刷新，因为默认的View enable为false的行为是透明度为原来的50%而不是改变drawable
    invalidate(true);

    if (!enabled) {
        cancelPendingInputEvents();
    }
}      
    
兄弟们，看见没，看见没！这三个方法里面都会调用关键的setFlags()方法，这方法到底是何方神圣！让我们慢慢揭开其神秘的面纱吧
        
  
        
    
/**
    
    
      * Set flags controlling behavior of this view.
    
    
      *设置标记来控制视图的状态
    
    
      *
    
    
      * @param flags Constant indicating the value which should be set 表示应该要被设置的值常量
    
    
      * @param mask Constant indicating the bit range that should be changed  表示应该要被改变的位的常量
    
    
      */
    
    
     该函数在View中多处被调用，例如 View.setEnable()、View.setClickable(),setFocusable()等很多函数都调用到该函数。
    
    
     在View中使用mViewFlags和mPrivateFlags变量保存大多数的属性：
    
    
     – mViewFlags：该标记用来保存和视图状态相关的属性。
    
    
     – mPrivateFlags 该标记用来保存和内部逻辑相关的属性
    
    
     如Visible相关的Flag：
    
    
     
            
public static final int VISIBLE = 0x00000000;
public static final int INVISIBLE = 0x00000004;
public static final int GONE = 0x00000008;
static final int VISIBILITY_MASK = 0x0000000C;      
        
 
   
   void setFlags(int flags, int mask) {    final boolean accessibilityEnabled =    AccessibilityManager.getInstance(mContext).isEnabled();    final boolean oldIncludeForAccessibility = accessibilityEnabled && includeForAccessibility();   
    int old = mViewFlags;//记录原来的视图状态标记    mViewFlags = (mViewFlags & ~mask) | (flags & mask);//更新视图状态标记   
    int changed = mViewFlags ^ old;//异或判断状态是否发生改变    if (changed == 0) {//如果没有改变，立刻返回    return;    }    int privateFlags = mPrivateFlags;//记录当前逻辑属性标记   
     检查Focusable位有没有改变    if (((changed & FOCUSABLE_MASK) != 0) &&    ((privateFlags & PFLAG_HAS_BOUNDS) !=0)) {    if (((old & FOCUSABLE_MASK) == FOCUSABLE)    && ((privateFlags & PFLAG_FOCUSED) != 0)) {    如果不再是focusable清空焦点。    clearFocus();    } else if (((old & FOCUSABLE_MASK) == NOT_FOCUSABLE)    && ((privateFlags & PFLAG_FOCUSED) == 0)) {        if (mParent != null) mParent.focusableViewAvailable(this);    }    }   
    final int newVisibility = flags & VISIBILITY_MASK;    if (newVisibility == VISIBLE) {    if ((changed & VISIBILITY_MASK) != 0) {        mPrivateFlags |= PFLAG_DRAWN;    invalidate(true);   
    needGlobalAttributesUpdate(true);   
    // a view becoming visible is worth notifying the parent    // about in case nothing has focus. even if this specific view    // isn't focusable, it may contain something that is, so let    // the root view try to give this focus if nothing else does.   一个视图将要变成可见的值得通知父控件假设没有东西有焦点。即使指定的视图不是   可获取焦点的，它可能包含了一些能获取焦点的，因此让根视图尝试让其获取焦点。    if ((mParent != null) && (mBottom > mTop) && (mRight > mLeft)) {//可见需要获取焦点    mParent.focusableViewAvailable(this);    }    }    }   
         检查GONE标志位是否发生改变    if ((changed & GONE) != 0) {    needGlobalAttributesUpdate(false);    requestLayout();//如果Gone的标志位发生了改变，必然会请求重新Layout   
    if (((mViewFlags & VISIBILITY_MASK) == GONE)) {    if (hasFocus()) clearFocus();//如果变为gone，且当前是有焦点的，清除焦点    clearAccessibilityFocus();//清除可达的焦点    destroyDrawingCache();    if (mParent instanceof View) {    // GONE views noop invalidation, so invalidate the parent    ((View) mParent).invalidate(true);//Gone的View不需要刷新，因此刷新它的父控件。    }    // Mark the view drawn to ensure that it gets invalidated properly the next    // time it is visible and gets invalidated   设置DRAWN标记保证其正确地得到刷新下次为可见并且刷新的时候    mPrivateFlags |= PFLAG_DRAWN;    }    if (mAttachInfo != null) {    mAttachInfo.mViewVisibilityChanged = true;    }    }   
        if ((changed & INVISIBLE) != 0) {    needGlobalAttributesUpdate(false);        mPrivateFlags |= PFLAG_DRAWN; = 0x00000020;   
    if (((mViewFlags & VISIBILITY_MASK) == INVISIBLE)) {    // root view becoming invisible shouldn't clear focus and accessibility focus   如果这是根视图的话，不应该清除焦点和可达的焦点。    if (getRootView() != this) {    if (hasFocus()) clearFocus();    clearAccessibilityFocus();    }    }    if (mAttachInfo != null) {    mAttachInfo.mViewVisibilityChanged = true;    }    }   
    if ((changed & VISIBILITY_MASK) != 0) {    // If the view is invisible, cleanup its display list to free up resources   如果视图不可见，清除它的显示列表以释放资源    if (newVisibility != VISIBLE && mAttachInfo != null) {    cleanupDraw();    }   
    if (mParent instanceof ViewGroup) {    ((ViewGroup) mParent).onChildVisibilityChanged(this,    (changed & VISIBILITY_MASK), newVisibility);//回调可见性发生变化    ((View) mParent).invalidate(true);    } else if (mParent != null) {    mParent.invalidateChild(this, null);    }   
    if (mAttachInfo != null) {    dispatchVisibilityChanged(this, newVisibility);//分发可见性发生变化    notifySubtreeAccessibilityStateChangedIfNeeded();    }    }   
    if ((changed & WILL_NOT_CACHE_DRAWING) != 0) {    destroyDrawingCache();    }   
    if ((changed & DRAWING_CACHE_ENABLED) != 0) {    destroyDrawingCache();    mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;    invalidateParentCaches();    }   
    if ((changed & DRAWING_CACHE_QUALITY_MASK) != 0) {    destroyDrawingCache();    mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;    }    static final int DRAW_MASK = 0x00000080;16*8=128---10000000    if ((changed & DRAW_MASK) != 0) {//检查DRAW_MASK标志位是否发生改变    if ((mViewFlags & WILL_NOT_DRAW) != 0) {    if (mBackground != null    || (mForegroundInfo != null && mForegroundInfo.mDrawable != null)) {    mPrivateFlags &= ~PFLAG_SKIP_DRAW;    } else {    mPrivateFlags |= PFLAG_SKIP_DRAW;    }    } else {    mPrivateFlags &= ~PFLAG_SKIP_DRAW;    }    requestLayout();//这里也会重新请求Layout，如果draw_mask标志位发生了改变，也会重新Layout    invalidate(true);    }   
    if ((changed & KEEP_SCREEN_ON) != 0) {    if (mParent != null && mAttachInfo != null && !mAttachInfo.mRecomputeGlobalAttributes) {    mParent.recomputeViewAttributes(this);    }    }   
    if (accessibilityEnabled) {    //focus,visibilty,click,longclick,contextClick    if ((changed & FOCUSABLE_MASK) != 0 || (changed & VISIBILITY_MASK) != 0    || (changed & CLICKABLE) != 0 || (changed & LONG_CLICKABLE) != 0    || (changed & CONTEXT_CLICKABLE) != 0) {    if (oldIncludeForAccessibility != includeForAccessibility()) {    notifySubtreeAccessibilityStateChangedIfNeeded();// Notifies that the accessibility state of this view changed.    } else {    notifyViewAccessibilityStateChangedIfNeeded(    AccessibilityEvent.CONTENT_CHANGE_TYPE_UNDEFINED);    }    } else if ((changed & ENABLED_MASK) != 0) {    notifyViewAccessibilityStateChangedIfNeeded(    AccessibilityEvent.CONTENT_CHANGE_TYPE_UNDEFINED);    }    }   }   
   总结一下：   ①View的许多关于属性的set方法，内部都会调用setFlag方法，来通过Flag标志控制View的行为。其中:      mViewFlags：该标记用来保存和视图状态相关的属性。    mPrivateFlags 该标记用来保存和内部逻辑相关的属性    ②View的可见性变为Gone的时候，都会调用requestLayout方法，请求parent重新measure和Layout。   ③此外，如果DRAW_MASK标志位发生了改变，也会调用requestLayout方法和invalidate方法来刷新。  ④可见性发生变化的时候，会设置PFLAG_DRAWN标志来确保刷新的时候得到重绘。
⑤如果视图不可见，清除它的显示列表以释放资源，调用cleanupDraw()方法。 
 
今天，关于setFlag方法的一些了解就到这里啦，期待下一篇博文吧