1 public static class LayoutParams{...}

LayoutParams are used by views to tell their parents how they want to be laid out.

The base LayoutParams class just describes how big the view wants to be for both width and height.

For each dimension, it can specify one of:
     FILL_PARENT (renamed MATCH_PARENT in API Level 8 and higher), which means that the view wants to be as big as its parent (minus padding)
     WRAP_CONTENT, which means that the view wants to be just big enough to enclose its content (plus padding)
     an exact number
There are subclasses of LayoutParams for different subclasses of ViewGroup. For example, AbsoluteLayout has its own subclass of LayoutParams which adds an X and Y value.

1 TextView tv = new TextView(this);
2         tv.setText("hello world");
3         linearlayout.addView(tv);

/*Adds a child view. If no layout parameters are already set on the child, the default parameters for this ViewGroup are set on the child.
添加一个view。如果这个view没有layout parameters参数定义，那么就采取默认参数。
*/

　　public void addView(View child) {

        addView(child, -1);

　　}

public void addView(View child, int index) {
        LayoutParams params = child.getLayoutParams();
        if (params == null) {
            params = generateDefaultLayoutParams();
            if (params == null) {
                throw new IllegalArgumentException("generateDefaultLayoutParams() cannot return null");
            }
        }
        addView(child, index, params);
}

protected LayoutParams generateDefaultLayoutParams() {
        return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    }

@Override
    protected LayoutParams generateDefaultLayoutParams() {
        if (mOrientation == HORIZONTAL) {
            return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        } else if (mOrientation == VERTICAL) {
            return new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
        }
        return null;
    }

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

        // 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);
}

private void addViewInner(View child, int index, LayoutParams params,
            boolean preventRequestLayout) {
//当ViewGroup中的object改变时，mTransition用以处理动画效果，此对象的类是LayoutTransition
        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);
        }
//addView(view)时会检查view是不是具有ViewParent，如果有，就会抛出下面的异常，一个view只能有一个ViewParent。注：ViewParent是一个接口，ViewGroup实现了此接口。
        if (child.getParent() != null) {
            throw new IllegalStateException("The specified child already has a parent. " +
                    "You must call removeView() on the child\'s parent first.");
        }
//这里的addChild并非是将view添加至ViewGroup中，这里是在处理动画效果
        if (mTransition != null) {
            mTransition.addChild(this, child);
        }
//检查params是否为空
        if (!checkLayoutParams(params)) {
            params = generateLayoutParams(params);
        }
//preventRequestLayout参数的含义是：是否禁止这个child去requestLayout()，原因是当使用直接赋值的时候，不会触发任何方法，但是当使用setLayoutParams()方法时，此方法中会去调用requestLayout()。不过View中的mLayoutParams参数被注解成了hide，无法在我们自定义的类中直接赋值。
        if (preventRequestLayout) {
            child.mLayoutParams = params;
        } else {
            child.setLayoutParams(params);
        }

        if (index < 0) {
            index = mChildrenCount;
        }
//addInArray()方法是将child添加到ViewGroup的mChildren对象中，mChildren是一个View[]类对象。
        addInArray(child, index);
//assignParent()函数给child分配指定parent，并进行requestLayout()，采用preventRequestLayout进行判断，与上边的setLayoutParams()结合，可以保证child只调用一个requestLayout()
        // tell our children
        if (preventRequestLayout) {
            child.assignParent(this);
        } else {
            child.mParent = this;
        }
//焦点
        if (child.hasFocus()) {
            requestChildFocus(child, child.findFocus());
        }
//和view所处环境相关的参数的设置
        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();
        }
//回调
        onViewAdded(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.isImportantForAccessibility() && child.getVisibility() != View.GONE) {
            notifySubtreeAccessibilityStateChangedIfNeeded();
        }
    }


//addViewInner()函数中涉及到的setLayoutParams()的具体实现，可以看到view调用了requestLayout()。在我们分析的这个addView()方法中，由于view的parent是null，因此mParent instanceof ViewGroup 返回的是false。
    public void setLayoutParams(ViewGroup.LayoutParams params) {
        if (params == null) {
            throw new NullPointerException("Layout parameters cannot be null");
        }
        mLayoutParams = params;
        resolveLayoutParams();
        if (mParent instanceof ViewGroup) {
            ((ViewGroup) mParent).onSetLayoutParams(this, params);
        }
        requestLayout();
    }

public void addView(View child, int index, LayoutParams params) {
        // 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);
    }