protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	if (mOrientation == VERTICAL) {
		measureVertical(widthMeasureSpec, heightMeasureSpec);//Vertical layout
	} else {
		measureHorizontal(widthMeasureSpec, heightMeasureSpec);//Horizontal layout
	}
}

void measureVertical(int widthMeasureSpec, int heightMeasureSpec) {
	mTotalLength = 0;//Height of child view  
	int maxWidth = 0;
	int childState = 0;
	int alternativeMaxWidth = 0;//Maximum width of subview (excluding subview of layout_weight > 0)  
	int weightedMaxWidth = 0;//Maximum width of the subview (including only the subview of layout_weight > 0)  
	boolean allFillParent = true;//Whether the width of the subview is all fillParent is used for subsequent judgment on whether recalculation is necessary  
	float totalWeight = 0; //The sum of weight s of all child view s  

	//Number of child views (including only direct child views, such as Linear Layout 1)  
	//There are Textview 1, Linear Layout 2, TextView 2, respectively.  
	//Linear Layout 2 has multiple sub-view s. At this point, LinearLayout1's getVirtualChildCount(); 3)  
	final int count = getVirtualChildCount();
	
	//Linear Layout Width Mode 
	final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
	//Linear Layout Height Mode  
	final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
	
	//The width of the child view is determined by the parent. If the parent LinearLayout is layout_width=wrap_content,  
	//If the child view is fill_parent, matchWidth =true  
	boolean matchWidth = false;
	boolean skippedMeasure = false;

	//baseLine of the number of sub view s in LinearLayout is used as the baseLine of LinearLayout       
	final int baselineChildIndex = mBaselineAlignedChildIndex;        
	final boolean useLargestChild = mUseLargestChild;

	int largestChildHeight = Integer.MIN_VALUE;

	if (sDebugLayout) {
		Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] + Pass.1, this=" + this);
	}

	// See how tall everyone is. Also remember max width.
	for (int i = 0; i < count; ++i) {
		final View child = getVirtualChildAt(i);

		if (child == null) {
			mTotalLength += measureNullChild(i);//By default, all return 0. Extended reservation is useless here.  
			continue;
		}

		if (child.getVisibility() == View.GONE) {
		   i += getChildrenSkipCount(child, i);//By default, all return 0. Extended reservation is useless here.  
		   continue;
		}

		if (sDebugLayout) {
			Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] + Child in Pass1: " + i + ", child=" + child
					+ ", this=" + this);
		}

		if (hasDividerBeforeChildAt(i)) {
			mTotalLength += mDividerHeight;
		}

		//Layout Params of child
		LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) child.getLayoutParams();

		totalWeight += lp.weight;
		
		if (heightMode == MeasureSpec.EXACTLY && lp.height == 0 && lp.weight > 0) {
			// Optimization: don't bother measuring children who are going to use
			// leftover space. These views will get measured again down below if
			// there is any leftover space.
			final int totalLength = mTotalLength;
			//If the Linear Layout height is determined. And the height of this child view is equal to 0, weight > 0,  
			//Then mTotal Length only needs to add margin.  
			//Because it's weight > 0; the view's specific height will be calculated later.  
			mTotalLength = Math.max(totalLength, totalLength + lp.topMargin + lp.bottomMargin);

			if (sDebugLayout) {
				Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Child in Pass1-1: " + i
						+ ", child=" + child + ", this=" + this + ", "
						+ "status=Skipped, mTotalLength=" + mTotalLength
						+ ", totalWeight=" + totalWeight);
			}
			skippedMeasure = true;
	   } else {
			int oldHeight = Integer.MIN_VALUE;

			if (lp.height == 0 && lp.weight > 0) {
				// heightMode is either UNSPECIFIED or AT_MOST, and this
				// child wanted to stretch to fill available space.
				// Translate that to WRAP_CONTENT so that it does not end up
				// with a height of 0
				oldHeight = 0;
				lp.height = LayoutParams.WRAP_CONTENT;

				if (sDebugLayout) {
					Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Child in Pass1-2-1: " + i
							+ ", child=" + child + ", this=" + this + ", "
							+ "status=Modified, LayoutParams.height change to WRAP_CONTENT");
				}
			}

			// Determine how big this child would like to be. If this or
			// previous children have given a weight, then we allow it to
			// use all available space (and we will shrink things later
			// if needed).
			measureChildBeforeLayout(
				   child, i, widthMeasureSpec, 0, heightMeasureSpec,
				   totalWeight == 0 ? mTotalLength : 0);

			if (oldHeight != Integer.MIN_VALUE) {
			   lp.height = oldHeight;
			}

			final int childHeight = child.getMeasuredHeight();
			final int totalLength = mTotalLength;
			mTotalLength = Math.max(totalLength, totalLength + childHeight + lp.topMargin +
				   lp.bottomMargin + getNextLocationOffset(child));

			if (useLargestChild) {//Whether android: measure WithLargestChild is set
				largestChildHeight = Math.max(childHeight, largestChildHeight);
			}

			if (sDebugLayout) {
				Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Child in Pass1-2-2: " + i
						+ ", child=" + child + ", this=" + this + ", "
						+ "status=Measured, mTotalLength=" + mTotalLength
						+ ", totalWeight=" + totalWeight);
			}
		}

		/**
		 * If applicable, compute the additional offset to the child's baseline
		 * we'll need later when asked {@link #getBaseline}.
		 */
		if ((baselineChildIndex >= 0) && (baselineChildIndex == i + 1)) {
		   mBaselineChildTop = mTotalLength;
		}

		// if we are trying to use a child index for our baseline, the above
		// book keeping only works if there are no children above it with
		// weight.  fail fast to aid the developer.
		if (i < baselineChildIndex && lp.weight > 0) {//i cannot be less than android: baseline Aligned ChildIndex with simultaneous weight > 0
			throw new RuntimeException("A child of LinearLayout with index "
					+ "less than mBaselineAlignedChildIndex has weight > 0, which "
					+ "won't work.  Either remove the weight, or don't set "
					+ "mBaselineAlignedChildIndex.");
		}

		boolean matchWidthLocally = false;
		if (widthMode != MeasureSpec.EXACTLY && lp.width == LayoutParams.MATCH_PARENT) {
			// The width of the linear layout will scale, and at least one
			// child said it wanted to match our width. Set a flag
			// indicating that we need to remeasure at least that view when
			// we know our width.
			//If the LinearLayout width is not determined, such as wrap_content, and the child view is FILL_PARENT,  
			//Then mark matchWidth=true; matchWidthLocally = true;  
			matchWidth = true;
			matchWidthLocally = true;
		}

		final int margin = lp.leftMargin + lp.rightMargin;
		final int measuredWidth = child.getMeasuredWidth() + margin;
		maxWidth = Math.max(maxWidth, measuredWidth);//Width of Maximum Subview  
		childState = combineMeasuredStates(childState, child.getMeasuredState());
	   //Is the child view width all FILL_PARENT?  
		allFillParent = allFillParent && lp.width == LayoutParams.MATCH_PARENT;
	   if (lp.weight > 0) {
			/*
			 * Widths of weighted Views are bogus if we end up
			 * remeasuring, so keep them separate.
			 */
			//If the parent width is wrap_content and the child fill_parent, the width of the child needs to be determined by the parent. This is not the true width.  
			weightedMaxWidth = Math.max(weightedMaxWidth,
					matchWidthLocally ? margin : measuredWidth);
		} else {
			alternativeMaxWidth = Math.max(alternativeMaxWidth,
					matchWidthLocally ? margin : measuredWidth);
		}

		if (sDebugLayout) {
			Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Child in Pass1: " + i + ", child=" + child
					+ ", this=" + this + ", " + "matchWidth=" + matchWidth
					+ ", matchWidthLocally=" + matchWidthLocally + ", "
					+ "weightedMaxWidth=" + weightedMaxWidth
					+ ", alternativeMaxWidth=" + alternativeMaxWidth);
		}

		i += getChildrenSkipCount(child, i);
	}

	if (sDebugLayout) {
		Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Pass.1, this=" + this + ", "
				+ "maxWidth=" + maxWidth + ", weightedMaxWidth=" + weightedMaxWidth
				+ ", alternativeMaxWidth=" + alternativeMaxWidth + ", "
				+ "mTotalLength=" + mTotalLength + ", totalWeight=" + totalWeight);
	}

	if (mTotalLength > 0 && hasDividerBeforeChildAt(count)) {
		mTotalLength += mDividerHeight;
	}

	if (useLargestChild &&
			(heightMode == MeasureSpec.AT_MOST || heightMode == MeasureSpec.UNSPECIFIED)) {
		if (sDebugLayout) {
			Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] + Pass.1.5, this=" + this);
		}

		mTotalLength = 0;

		for (int i = 0; i < count; ++i) {
			final View child = getVirtualChildAt(i);

			if (child == null) {
				mTotalLength += measureNullChild(i);
				continue;
			}

			if (child.getVisibility() == GONE) {
				i += getChildrenSkipCount(child, i);
				continue;
			}

			final LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams)
					child.getLayoutParams();
			// Account for negative margins
			final int totalLength = mTotalLength;
			mTotalLength = Math.max(totalLength, totalLength + largestChildHeight +
					lp.topMargin + lp.bottomMargin + getNextLocationOffset(child));
		}

		if (sDebugLayout) {
			Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Pass.1.5, this=" + this
					+ ", largestChildHeight=" + largestChildHeight
					+ ", mTotalLength=" + mTotalLength);
		}
	}

	// Add in our padding
	mTotalLength += mPaddingTop + mPaddingBottom;

	int heightSize = mTotalLength;

	// Check against our minimum height
	heightSize = Math.max(heightSize, getSuggestedMinimumHeight());
	
	// Reconcile our calculated size with the heightMeasureSpec
	int heightSizeAndState = resolveSizeAndState(heightSize, heightMeasureSpec, 0);
	heightSize = heightSizeAndState & MEASURED_SIZE_MASK;
	
	// Either expand children with weight to take up available space or
	// shrink them if they extend beyond our current bounds. If we skipped
	// measurement on any children, we need to measure them now.
	int delta = heightSize - mTotalLength;
	if (sDebugLayout) {
		Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] + Pass.2, this=" + this + ", "
				+ "delta=" + delta + ", " + "heightSize=" + heightSize
				+ ", mTotalLength=" + mTotalLength);
	}
	//SkppedMeasure = true: If the height of LinearLayout is determined and there are child view s with height=0, weight > 0,  
	if (skippedMeasure || delta != 0 && totalWeight > 0.0f) {
		float weightSum = mWeightSum > 0.0f ? mWeightSum : totalWeight;

		mTotalLength = 0;

		for (int i = 0; i < count; ++i) {
			final View child = getVirtualChildAt(i);
			
			if (child.getVisibility() == View.GONE) {
				continue;
			}
			
			if (sDebugLayout) {
				Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] + Child in Pass2: " + i + ", "
						+ "child=" + child + ", this=" + this);
			}

			LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) child.getLayoutParams();
			
			float childExtra = lp.weight;
			if (childExtra > 0) {
				// Child said it could absorb extra space -- give him his share
				int share = (int) (childExtra * delta / weightSum);
				weightSum -= childExtra;
				delta -= share;

				final int childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec,
						mPaddingLeft + mPaddingRight +
								lp.leftMargin + lp.rightMargin, lp.width);

				// TODO: Use a field like lp.isMeasured to figure out if this
				// child has been previously measured
				if ((lp.height != 0) || (heightMode != MeasureSpec.EXACTLY)) {
					// child was measured once already above...
					// base new measurement on stored values
					int childHeight = child.getMeasuredHeight() + share;
					if (childHeight < 0) {
						childHeight = 0;
					}
					
					child.measure(childWidthMeasureSpec,
							MeasureSpec.makeMeasureSpec(childHeight, MeasureSpec.EXACTLY));

					if (sDebugLayout) {
						Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Child in Pass2-1-1-1: " + i
								+ ", child=" + child + ", this=" + this + ", "
								+ "status=Measured, share=" + share
								+ ", childHeight=" + childHeight
								+ ", mTotalLength=" + mTotalLength);
					}
				} else {
					// child was skipped in the loop above.
					// Measure for this first time here      
					child.measure(childWidthMeasureSpec,
							MeasureSpec.makeMeasureSpec(share > 0 ? share : 0,
									MeasureSpec.EXACTLY));

					if (sDebugLayout) {
						Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Child in Pass2-1-1-2: " + i
								+ ", child=" + child + ", this=" + this + ", "
								+ "status=Measured, share=" + share
								+ ", mTotalLength=" + mTotalLength);
					}
				}

				// Child may now not fit in vertical dimension.
				childState = combineMeasuredStates(childState, child.getMeasuredState()
						& (MEASURED_STATE_MASK>>MEASURED_HEIGHT_STATE_SHIFT));
			} else {
				if (sDebugLayout) {
					Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Child in Pass2-1-2: " + i
							+ ", child=" + child + ", this=" + this + ", "
							+ "status=Skipped, ChildExtra=" + childExtra
							+ ", mTotalLength=" + mTotalLength);
				}
			}

			final int margin =  lp.leftMargin + lp.rightMargin;
			final int measuredWidth = child.getMeasuredWidth() + margin;
			maxWidth = Math.max(maxWidth, measuredWidth);

			boolean matchWidthLocally = widthMode != MeasureSpec.EXACTLY &&
					lp.width == LayoutParams.MATCH_PARENT;

			alternativeMaxWidth = Math.max(alternativeMaxWidth,
					matchWidthLocally ? margin : measuredWidth);

			allFillParent = allFillParent && lp.width == LayoutParams.MATCH_PARENT;

			final int totalLength = mTotalLength;
			mTotalLength = Math.max(totalLength, totalLength + child.getMeasuredHeight() +
					lp.topMargin + lp.bottomMargin + getNextLocationOffset(child));
		}

		// Add in our padding
		mTotalLength += mPaddingTop + mPaddingBottom;

		if (sDebugLayout) {
			Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Pass.2-1, this=" + this + ", "
					+ "maxWidth=" + maxWidth + ", weightedMaxWidth=" + weightedMaxWidth
					+ ", alternativeMaxWidth=" + alternativeMaxWidth + ", "
					+ "delta=" + delta + ", mTotalLength=" + mTotalLength);

		}
		// TODO: Should we recompute the heightSpec based on the new total length?
   } else {
		alternativeMaxWidth = Math.max(alternativeMaxWidth,
									   weightedMaxWidth);


		// We have no limit, so make all weighted views as tall as the largest child.
		// Children will have already been measured once.
		if (useLargestChild && heightMode != MeasureSpec.EXACTLY) {
			for (int i = 0; i < count; i++) {
				final View child = getVirtualChildAt(i);

				if (child == null || child.getVisibility() == View.GONE) {
					continue;
				}

				final LinearLayout.LayoutParams lp =
						(LinearLayout.LayoutParams) child.getLayoutParams();

				float childExtra = lp.weight;
				if (childExtra > 0) {
					child.measure(
							MeasureSpec.makeMeasureSpec(child.getMeasuredWidth(),
									MeasureSpec.EXACTLY),
							MeasureSpec.makeMeasureSpec(largestChildHeight,
									MeasureSpec.EXACTLY));
				}

				if (sDebugLayout) {
					String measureString = (childExtra > 0)
							? "status=Measured" : "status=Skipped";
					Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Child in Pass2-2: " + i
							+ ", child=" + child + ", this=" + this + ", " + measureString);
				}
			}
		}

		if (sDebugLayout) {
			Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Pass.2-2, this=" + this + ", "
					+ "maxWidth=" + maxWidth + ", weightedMaxWidth=" + weightedMaxWidth
					+ ", alternativeMaxWidth=" + alternativeMaxWidth + ", " + "delta=" + delta
					+ ", mTotalLength=" + mTotalLength
					+ ", useLargestChild=" + useLargestChild);
		}
	}

	if (!allFillParent && widthMode != MeasureSpec.EXACTLY) {
		maxWidth = alternativeMaxWidth;
	}
	
	maxWidth += mPaddingLeft + mPaddingRight;

	// Check against our minimum width
	maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());
	
	setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
			heightSizeAndState);

	if (matchWidth) {
		if (sDebugLayout) {
			Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] + Pass.3, this=" + this
					+ ", uniformWidth=" + getMeasuredWidth() + ", this=" + this);
		}

		forceUniformWidth(count, heightMeasureSpec);

		if (sDebugLayout) {
			Xlog.d(DEBUG_LOG_TAG, "[LinearLayout] - Pass.3, this=" + this);
		}
	}
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/doov_ll_root"
    android:layout_width="fill_parent"
    android:layout_height="480dip" >

    <LinearLayout
        android:id="@+id/doov_linear1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="#ff888888"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/doov_id1"
            android:layout_width="fill_parent"
            android:layout_height="0dip"
            android:layout_weight="2"
            android:background="#ff765423"
            android:text="11111" />

        <TextView
            android:id="@+id/doov_id2"
            android:layout_width="fill_parent"
            android:layout_height="0dip"
            android:layout_weight="1"
            android:background="#ffff0000"
            android:text="aaaaa" />

        <TextView
            android:id="@+id/doov_id3"
            android:layout_width="fill_parent"
            android:layout_height="90dip"
            android:background="#ff234532"
            android:text="2222222" />
    </LinearLayout>

</LinearLayout>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/doov_ll_root"
    android:layout_width="fill_parent"
    android:layout_height="480dip" >

    <LinearLayout
        android:id="@+id/doov_linear1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="#ff888888"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/doov_id1"
            android:layout_width="fill_parent"
            android:layout_height="match_parent"
            android:layout_weight="2"
            android:background="#ff765423"
            android:text="11111" />

        <TextView
            android:id="@+id/doov_id2"
            android:layout_width="fill_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:background="#ffff0000"
            android:text="aaaaa" />

        <TextView
            android:id="@+id/doov_id3"
            android:layout_width="fill_parent"
            android:layout_height="90dip"
            android:background="#ff234532"
            android:text="2222222" />
    </LinearLayout>

</LinearLayout>