[Android FrameWork 6.0源碼學習] ViewGroup的addView函數分析

Android中整個的View的組裝是採用組合模式。

ViewGroup就相當與樹根，各種Layout就相當於枝幹，各種子View，就相當於樹葉。

至於View類。我們就當它是個種子吧。哈哈！

ViewGroup屬於樹根，可以生長數很多枝幹（繼承自定義Layout）而枝幹上有可以長出很多葉子（TextView,ImageVIew......）

好，閑話少敘，接下來步入正題！

首先，關於View的操作方法，被定義在一個叫做ViewManager的介面中，介面中還有兩個方法，分別是移除和更新，這次主要分析addView

public interface ViewManager
    {
        /**
         * Assign the passed LayoutParams to the passed View and add the view to the window.
         * <p>Throws {@link android.view.WindowManager.BadTokenException} for certain programming
         * errors, such as adding a second view to a window without removing the first view.
         * <p>Throws {@link android.view.WindowManager.InvalidDisplayException} if the window is on a
         * secondary {@link Display} and the specified display can't be found
         * (see {@link android.app.Presentation}).
         * @param view The view to be added to this window.
         * @param params The LayoutParams to assign to view.
         */
        public void addView(View view, ViewGroup.LayoutParams params);
        public void updateViewLayout(View view, ViewGroup.LayoutParams params);
        public void removeView(View view)
　　}

 addView在ViewGroup中實現，接下來貼出代碼進行分析

    public void addView(View child, LayoutParams params) {
        addView(child, -1, params);
    }

這個方法中調用了自身的addView方法，並且多傳遞了一個-1，這個-1是View的索引，要插入的位置

    public void addView(View child, int index, LayoutParams params) {
        if (DBG) {
            System.out.println(this + " addView");
        }

        if (child == null) {
            throw new IllegalArgumentException("Cannot add a null child view to a ViewGroup");
        }

        // addViewInner() will call child.requestLayout() when setting the new LayoutParams
        // therefore, we call requestLayout() on ourselves before, so that the child's request
        // will be blocked at our level
        requestLayout();
        invalidate(true);
        addViewInner(child, index, params, false);
    }

 這個方法先是重繪了一下佈局，然後調用了addViewInner(child, index, params, false);方法，來把View插入到相應的位置

    private void addViewInner(View child, int index, LayoutParams params,
            boolean preventRequestLayout) {

        if (mTransition != null) {
            // Don't prevent other add transitions from completing, but cancel remove
            // transitions to let them complete the process before we add to the container
            mTransition.cancel(LayoutTransition.DISAPPEARING);
        }

        if (child.getParent() != null) {
            throw new IllegalStateException("The specified child already has a parent. " +
                    "You must call removeView() on the child's parent first.");
        }

        if (mTransition != null) {
            mTransition.addChild(this, child);
        }

        if (!checkLayoutParams(params)) {
            params = generateLayoutParams(params);
        }

        if (preventRequestLayout) {
            child.mLayoutParams = params;
        } else {
            child.setLayoutParams(params);
        }

        if (index < 0) {
            index = mChildrenCount;
        }

        //ViewGroup用一個View類型的數組去維護下邊的子view，這個方法就是把view添加到響應的位置上
        addInArray(child, index);

        //綁定插入的view的父容器為當前group
        // tell our children
        if (preventRequestLayout) {
            child.assignParent(this);
        } else {
            child.mParent = this;
        }

        if (child.hasFocus()) {
            requestChildFocus(child, child.findFocus());
        }

        AttachInfo ai = mAttachInfo;
        if (ai != null && (mGroupFlags & FLAG_PREVENT_DISPATCH_ATTACHED_TO_WINDOW) == 0) {
            boolean lastKeepOn = ai.mKeepScreenOn;
            ai.mKeepScreenOn = false;
            child.dispatchAttachedToWindow(mAttachInfo, (mViewFlags&VISIBILITY_MASK));
            if (ai.mKeepScreenOn) {
                needGlobalAttributesUpdate(true);
            }
            ai.mKeepScreenOn = lastKeepOn;
        }

        if (child.isLayoutDirectionInherited()) {
            child.resetRtlProperties();
        }

        dispatchViewAdded(child);

        if ((child.mViewFlags & DUPLICATE_PARENT_STATE) == DUPLICATE_PARENT_STATE) {
            mGroupFlags |= FLAG_NOTIFY_CHILDREN_ON_DRAWABLE_STATE_CHANGE;
        }

        if (child.hasTransientState()) {
            childHasTransientStateChanged(child, true);
        }

        if (child.getVisibility() != View.GONE) {
            notifySubtreeAccessibilityStateChangedIfNeeded();
        }

        if (mTransientIndices != null) {
            final int transientCount = mTransientIndices.size();
            for (int i = 0; i < transientCount; ++i) {
                final int oldIndex = mTransientIndices.get(i);
                if (index <= oldIndex) {
                    mTransientIndices.set(i, oldIndex + 1);
                }
            }
        }
    }

 這個方法先檢查一下LayoutParams，看看插入的該view是否存在長寬，如果沒有就生成一個預設的LayoutParams

然後判斷index是否小於0，小於0就賦值為當前容器中的個數，代表插入到最後一項

隨後就調用addInArray方法，來插入View到當前ViewGroup中，插入完成後給該view綁定一下父容器（getParent的值）

隨後就是一些焦點，監聽的分發，我們仔細分析一下插入方法就好了，就是addInArray

   private void addInArray(View child, int index) {
        View[] children = mChildren;
        final int count = mChildrenCount;
        final int size = children.length;
        if (index == count) {
            if (size == count) {
                mChildren = new View[size + ARRAY_CAPACITY_INCREMENT];
                System.arraycopy(children, 0, mChildren, 0, size);
                children = mChildren;
            }
            children[mChildrenCount++] = child;
        } else if (index < count) {
            if (size == count) {
                mChildren = new View[size + ARRAY_CAPACITY_INCREMENT];
                System.arraycopy(children, 0, mChildren, 0, index);
                System.arraycopy(children, index, mChildren, index + 1, count - index);
                children = mChildren;
            } else {
                System.arraycopy(children, index, children, index + 1, count - index);
            }
            children[index] = child;
            mChildrenCount++;
            if (mLastTouchDownIndex >= index) {
                mLastTouchDownIndex++;
            }
        } else {
            throw new IndexOutOfBoundsException("index=" + index + " count=" + count);
        }
    }

mChildren是ViewGroup中的一個View類型的數組，裡邊存放了該Group下的所有子View

ARRAY_CAPACITY_INCREMENT這個常量的值是12

首先判斷一下mChildren的位置還是否充足，不充足就繼續擴充12個位置出來，copy源數組內容進到新數組裡，然後再把本次要添加的view放到最後

如果index比count小，說明是插入操作，也是先判斷位置是否充足，不充足就擴充並且copy到index處，然後在把剩下的copy到index+1到末尾

這樣就把index位置空了出來。就完成了插入操作

插入完成後，系統會重繪界面，你就可以看到你插入的view了。

addView這個方法就分析完了，有什麼疑問就可以指出來，錯誤也一樣。共同學習共同進步。