自定义view中onSizeChanged、onFinishInflate方法调用时机

r囧r小猫 2022-06-04 01:58 269阅读 0赞

转自：[http://blog.csdn.net/anhenzhufeng/article/details/72886181][http_blog.csdn.net_anhenzhufeng_article_details_72886181]

一般自定义View或ViewGroup基本上都会去实现onMeasure、onLayout、onDraw方法  
**还有另外两个方法是onFinishInflate和onSizeChanged**

### onFinishInflate ###

onFinishInflate方法只有在布局文件中加载View实例会回调，如果直接new一个View的话是不会回调的。  
如果是一个ViewGroup，只有它和它的子View完全被加载实例化了之后才会回调该ViewGroup的这个方法  
因为在LayoutInflater的inflate执行过程中最终的调用路径是：inflate -> rInflateChildren -> rInflate

其中inflate的调用是这样的：

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
        synchronized (mConstructorArgs) {
            Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
    
            final Context inflaterContext = mContext;
            final AttributeSet attrs = Xml.asAttributeSet(parser);
            Context lastContext = (Context) mConstructorArgs[0];
            mConstructorArgs[0] = inflaterContext;
            View result = root;
    
            try {
                // Look for the root node.
                int type;
                while ((type = parser.next()) != XmlPullParser.START_TAG &&
                        type != XmlPullParser.END_DOCUMENT) {
                    // Empty
                }
    
                if (type != XmlPullParser.START_TAG) {
                    throw new InflateException(parser.getPositionDescription()
                            + ": No start tag found!");
                }
    
                final String name = parser.getName();
    
                if (DEBUG) {
                    System.out.println("**************************");
                    System.out.println("Creating root view: "
                            + name);
                    System.out.println("**************************");
                }
    
                if (TAG_MERGE.equals(name)) {
                    if (root == null || !attachToRoot) {
                        throw new InflateException("<merge /> can be used only with a valid "
                                + "ViewGroup root and attachToRoot=true");
                    }
    
                    rInflate(parser, root, inflaterContext, attrs, false);
                } else {
                    // Temp is the root view that was found in the xml
                    final View temp = createViewFromTag(root, name, inflaterContext, attrs);
    
                    ViewGroup.LayoutParams params = null;
    
                    if (root != null) {
                        if (DEBUG) {
                            System.out.println("Creating params from root: " +
                                    root);
                        }
                        // Create layout params that match root, if supplied
                        params = root.generateLayoutParams(attrs);
                        if (!attachToRoot) {
                            // Set the layout params for temp if we are not
                            // attaching. (If we are, we use addView, below)
                            temp.setLayoutParams(params);
                        }
                    }
    
                    if (DEBUG) {
                        System.out.println("-----> start inflating children");
                    }
    
                    // Inflate all children under temp against its context.
                    rInflateChildren(parser, temp, attrs, true);
    
                    if (DEBUG) {
                        System.out.println("-----> done inflating children");
                    }
    
                    // We are supposed to attach all the views we found (int temp)
                    // to root. Do that now.
                    if (root != null && attachToRoot) {
                        root.addView(temp, params);
                    }
    
                    // Decide whether to return the root that was passed in or the
                    // top view found in xml.
                    if (root == null || !attachToRoot) {
                        result = temp;
                    }
                }
    
            } catch (XmlPullParserException e) {
                final InflateException ie = new InflateException(e.getMessage(), e);
                ie.setStackTrace(EMPTY_STACK_TRACE);
                throw ie;
            } catch (Exception e) {
                final InflateException ie = new InflateException(parser.getPositionDescription()
                        + ": " + e.getMessage(), e);
                ie.setStackTrace(EMPTY_STACK_TRACE);
                throw ie;
            } finally {
                // Don't retain static reference on context.
                mConstructorArgs[0] = lastContext;
                mConstructorArgs[1] = null;
    
                Trace.traceEnd(Trace.TRACE_TAG_VIEW);
            }
    
            return result;
        }
    }

然后，通过递归调用rInflate解析所有的xml节点，如下：

void rInflate(XmlPullParser parser, View parent, Context context,
            AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {
    
        final int depth = parser.getDepth();
        int type;
    
        while (((type = parser.next()) != XmlPullParser.END_TAG ||
                parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
    
            if (type != XmlPullParser.START_TAG) {
                continue;
            }
    
            final String name = parser.getName();
    
            if (TAG_REQUEST_FOCUS.equals(name)) {
                parseRequestFocus(parser, parent);
            } else if (TAG_TAG.equals(name)) {
                parseViewTag(parser, parent, attrs);
            } else if (TAG_INCLUDE.equals(name)) {
                if (parser.getDepth() == 0) {
                    throw new InflateException("<include /> cannot be the root element");
                }
                parseInclude(parser, context, parent, attrs);
            } else if (TAG_MERGE.equals(name)) {
                throw new InflateException("<merge /> must be the root element");
            } else {
                final View view = createViewFromTag(parent, name, context, attrs);
                final ViewGroup viewGroup = (ViewGroup) parent;
                final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
                rInflateChildren(parser, view, attrs, true);
                viewGroup.addView(view, params);
            }
        }
    
        if (finishInflate) {
            parent.onFinishInflate();
        }
    }

完成后，会有个判断

if (finishInflate) {
        parent.onFinishInflate();
    }

这时候通知父控件执行onFinishInflate方法，而此时仅仅是将所有的子控件实例化到内存中，也就是可以通过getChildAt()来获取相应的子控件实例了。  
这时候还没执行onMeasure呢，而通过layoutInflate.inflate出来的View或ViewGroup往往是要添加到已有的父控件，  
比如使用setContentView方式获取我们的xml文件，其中做了几个步骤：  
首先去xml中解析出我们的布局View  
然后在把这个View添加到Activity的顶级视图中（即DecorView的子布局content中），添加的过程必然使用到了addView的操作，而该操作就会触发requestLayout和invalidate这两个方法，  
这两个方法又必然会触发ViewParent（即ViewRootImpl）这个视图管理者的一系列操作，这一系列操作由performTraversalse开始，顺序去调用performMeasure -> view.measure -> onMeasure，performLayout -> view.layout -> onLayout，performDraw -> draw -> drawSoftWare -> view.draw -> onDraw（实现自身的绘制） -> dispatchDraw （实现子view的绘制，调用drawChild）。  
所以我们的onMeasure及后续的方法应该是在onFinishInflate之后调用的。

### onSizeChanged ###

onSizeChanged方法一般是视图大小发生变化的时候回调了，那么具体看源码是在layout的过程中出发的  
在layout方法中会调用setFrame方法，在setFrame方法中又调用了sizeChange，在该方法里面回调了onSizeChanged，然后才去回调onLayout过程

public void layout(int l, int t, int r, int b) {  
        if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {  
            onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);  
            mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;  
        }  
    
        int oldL = mLeft;  
        int oldT = mTop;  
        int oldB = mBottom;  
        int oldR = mRight;  
    
        boolean changed = isLayoutModeOptical(mParent) ?  
                setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);  
    
        if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {  
            onLayout(changed, l, t, r, b);  
    
            if (shouldDrawRoundScrollbar()) {  
                if(mRoundScrollbarRenderer == null) {  
                    mRoundScrollbarRenderer = new RoundScrollbarRenderer(this);  
                }  
            } else {  
                mRoundScrollbarRenderer = null;  
            }  
    
            mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;  
    
            ListenerInfo li = mListenerInfo;  
            if (li != null && li.mOnLayoutChangeListeners != null) {  
                ArrayList<OnLayoutChangeListener> listenersCopy =  
                        (ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();  
                int numListeners = listenersCopy.size();  
                for (int i = 0; i < numListeners; ++i) {  
                    listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);  
                }  
            }  
        }  
    
        mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;  
        mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;  
    }

setFrame过程：

protected boolean setFrame(int left, int top, int right, int bottom) {  
        boolean changed = false;  
    
        if (DBG) {  
            Log.d("View", this + " View.setFrame(" + left + "," + top + ","  
                    + right + "," + bottom + ")");  
        }  
    
        if (mLeft != left || mRight != right || mTop != top || mBottom != bottom) {  
            changed = true;  
    
            // Remember our drawn bit  
            int drawn = mPrivateFlags & PFLAG_DRAWN;  
    
            int oldWidth = mRight - mLeft;  
            int oldHeight = mBottom - mTop;  
            int newWidth = right - left;  
            int newHeight = bottom - top;  
            boolean sizeChanged = (newWidth != oldWidth) || (newHeight != oldHeight);  
    
            // Invalidate our old position  
            invalidate(sizeChanged);  
    
            mLeft = left;  
            mTop = top;  
            mRight = right;  
            mBottom = bottom;  
            mRenderNode.setLeftTopRightBottom(mLeft, mTop, mRight, mBottom);  
    
            mPrivateFlags |= PFLAG_HAS_BOUNDS;  
    
    
            if (sizeChanged) {  
                sizeChange(newWidth, newHeight, oldWidth, oldHeight);  
            }  
    
            if ((mViewFlags & VISIBILITY_MASK) == VISIBLE || mGhostView != null) {  
                // If we are visible, force the DRAWN bit to on so that  
                // this invalidate will go through (at least to our parent).  
                // This is because someone may have invalidated this view  
                // before this call to setFrame came in, thereby clearing  
                // the DRAWN bit.  
                mPrivateFlags |= PFLAG_DRAWN;  
                invalidate(sizeChanged);  
                // parent display list may need to be recreated based on a change in the bounds  
                // of any child  
                invalidateParentCaches();  
            }  
    
            // Reset drawn bit to original value (invalidate turns it off)  
            mPrivateFlags |= drawn;  
    
            mBackgroundSizeChanged = true;  
            if (mForegroundInfo != null) {  
                mForegroundInfo.mBoundsChanged = true;  
            }  
    
            notifySubtreeAccessibilityStateChangedIfNeeded();  
        }  
        return changed;  
    }

[http_blog.csdn.net_anhenzhufeng_article_details_72886181]: http://blog.csdn.net/anhenzhufeng/article/details/72886181