[Android FrameWork 6.0源码学习] ViewGroup的addView函数分析

Posted 2020-09-22

android中整个的View的组装是采用组合模式。

ViewGroup就相当与树根，各种Layout就相当于枝干，各种子View，就相当于树叶。

至于View类。我们就当它是个种子吧。哈哈！

ViewGroup属于树根，可以生长数很多枝干（继承自定义Layout）而枝干上有可以长出很多叶子（TextView,ImageVIew......）

好，闲话少叙，接下来步入正题！

首先，关于View的操作方法，被定义在一个叫做ViewManager的接口中，接口中还有两个方法，分别是移除和更新，这次主要分析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中实现，接下来贴出代码进行分析

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

这个方法中调用了自身的addView方法，并且多传递了一个-1，这个-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);
    }

这个方法先是重绘了一下布局，然后调用了addViewInner(child, index, params, false);方法，来把View插入到相应的位置

    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用一个View类型的数组去维护下边的子view，这个方法就是把view添加到响应的位置上
        addInArray(child, index);

        //绑定插入的view的父容器为当前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);
                }
            }
        }
    }

 这个方法先检查一下LayoutParams，看看插入的该view是否存在长宽，如果没有就生成一个默认的LayoutParams

然后判断index是否小于0，小于0就赋值为当前容器中的个数，代表插入到最后一项

随后就调用addInArray方法，来插入View到当前ViewGroup中，插入完成后给该view绑定一下父容器（getParent的值）

随后就是一些焦点，监听的分发，我们仔细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中的一个View类型的数组，里边存放了该Group下的所有子View

ARRAY_CAPACITY_INCREMENT这个常量的值是12

首先判断一下mChildren的位置还是否充足，不充足就继续扩充12个位置出来，copy源数组内容进到新数组里，然后再把本次要添加的view放到最后

如果index比count小，说明是插入操作，也是先判断位置是否充足，不充足就扩充并且copy到index处，然后在把剩下的copy到index+1到末尾

这样就把index位置空了出来。就完成了插入操作

插入完成后，系统会重绘界面，你就可以看到你插入的view了。

 

addView这个方法就分析完了，有什么疑问就可以指出来，错误也一样。共同学习共同进步。