Android View measure (3) Common Methods

Android View measure (3) Common Methods

 

ViewGroup. measureChildren ()
ViewGroup. measureChild ()
ViewGroup. measureChildWithMargins ()

 

 

 

/*** Ask one of the children of this view to measure itself, taking into * account both the MeasureSpec requirements for this view and its padding * and margins. the child must have MarginLayoutParams The heavy lifting is * done in getChildMeasureSpec. ** @ param child The child to measure * @ param parentWidthMeasureSpec The width requirements for this view * @ param widthUsed Extra space that has been used up by the parent * horizontally (possibly by other children of the parent) * @ param parentHeightMeasureSpec The height requirements for this view * @ param heightUsed Extra space that has been used up by the parent * vertically (possibly by other children of the parent) */protected void measureChildWithMargins (View child, int parentWidthMeasureSpec, int widthUsed, int second, int heightUsed) {// type conversion final MarginLayoutParams lp = (marginlayoutyoutparams child. getLayoutParams (); // 2 getChildMeasureSpec method final int childWidthMeasureSpec = getChildMeasureSpec (parentWidthMeasureSpec, mPaddingLeft + mPaddingRight + lp. leftMargin + lp. rightMargin + widthUsed, lp. width); final int childHeightMeasureSpec = getChildMeasureSpec (parentHeightMeasureSpec, mPaddingTop + mPaddingBottom + lp. topMargin + lp. bottomMargin + heightUsed, lp. height); child. measure (childWidthMeasureSpec, childHeightMeasureSpec );}

 

This method performs the Measure operation on the Child view passed by the first parameter.
1. The passed sub-view LayoutParams must be or inherit from MarginLayoutParams. Otherwise, a conversion exception is thrown.

    /**     * Does the hard part of measureChildren: figuring out the MeasureSpec to     * pass to a particular child. This method figures out the right MeasureSpec     * for one dimension (height or width) of one child view.     *     * The goal is to combine information from our MeasureSpec with the     * LayoutParams of the child to get the best possible results. For example,     * if the this view knows its size (because its MeasureSpec has a mode of     * EXACTLY), and the child has indicated in its LayoutParams that it wants     * to be the same size as the parent, the parent should ask the child to     * layout given an exact size.     *     * @param spec The requirements for this view     * @param padding The padding of this view for the current dimension and     *        margins, if applicable     * @param childDimension How big the child wants to be in the current     *        dimension     * @return a MeasureSpec integer for the child     */    public static int getChildMeasureSpec(int spec, int padding, int childDimension) {        int specMode = MeasureSpec.getMode(spec);        int specSize = MeasureSpec.getSize(spec);        int size = Math.max(0, specSize - padding);        int resultSize = 0;        int resultMode = 0;        switch (specMode) {        // Parent has imposed an exact size on us        case MeasureSpec.EXACTLY:            if (childDimension >= 0) {                resultSize = childDimension;                resultMode = MeasureSpec.EXACTLY;            } else if (childDimension == LayoutParams.FILL_PARENT) {                // Child wants to be our size. So be it.                resultSize = size;                resultMode = MeasureSpec.EXACTLY;            } else if (childDimension == LayoutParams.WRAP_CONTENT) {                // Child wants to determine its own size. It can't be                // bigger than us.                resultSize = size;                resultMode = MeasureSpec.AT_MOST;            }            break;        // Parent has imposed a maximum size on us        case MeasureSpec.AT_MOST:            if (childDimension >= 0) {                // Child wants a specific size... so be it                resultSize = childDimension;                resultMode = MeasureSpec.EXACTLY;            } else if (childDimension == LayoutParams.FILL_PARENT) {                // Child wants to be our size, but our size is not fixed.                // Constrain child to not be bigger than us.                resultSize = size;                resultMode = MeasureSpec.AT_MOST;            } else if (childDimension == LayoutParams.WRAP_CONTENT) {                // Child wants to determine its own size. It can't be                // bigger than us.                resultSize = size;                resultMode = MeasureSpec.AT_MOST;            }            break;        // Parent asked to see how big we want to be        case MeasureSpec.UNSPECIFIED:            if (childDimension >= 0) {                // Child wants a specific size... let him have it                resultSize = childDimension;                resultMode = MeasureSpec.EXACTLY;            } else if (childDimension == LayoutParams.FILL_PARENT) {                // Child wants to be our size... find out how big it should                // be                resultSize = 0;                resultMode = MeasureSpec.UNSPECIFIED;            } else if (childDimension == LayoutParams.WRAP_CONTENT) {                // Child wants to determine its own size.... find out how                // big it should be                resultSize = 0;                resultMode = MeasureSpec.UNSPECIFIED;            }            break;        }        return MeasureSpec.makeMeasureSpec(resultSize, resultMode);    }

 

 

 

Protected void measureChildWithMargins (View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed) {// 1 .... // 2 getChildMeasureSpec method final int childWidthMeasureSpec = getChildMeasureSpec (parentWidthMeasureSpec, mPaddingLeft + mPaddingRight + lp. leftMargin + lp. rightMargin + widthUsed, lp. width );}

 

Call this method to see the specific meanings of the three parameters.
1. spec: The specification required by this view [parentWidthMeasureSpec]
2. padding: the padding value of the current ViewGroup view and the margin value of the imported sub-view [mPaddingLeft + mPaddingRight + lp. leftMargin + lp. rightMargin + widthUsed ]? WidthUsed
3. childDimension: the input parameter view. The expected value is "lp. width]

** For example

Extended: MeasureSpec method and splicing Method

 

 

 

    /**     * Utility to reconcile a desired size with constraints imposed by a MeasureSpec.     * Will take the desired size, unless a different size is imposed by the constraints.     *     * @param size How big the view wants to be     * @param measureSpec Constraints imposed by the parent     * @return The size this view should be.     */    public static int resolveSize(int size, int measureSpec) {        int result = size;        int specMode = MeasureSpec.getMode(measureSpec);        int specSize =  MeasureSpec.getSize(measureSpec);        switch (specMode) {        case MeasureSpec.UNSPECIFIED:            result = size;            break;        case MeasureSpec.AT_MOST:            result = Math.min(size, specSize);            break;        case MeasureSpec.EXACTLY:            result = specSize;            break;        }        return result;    }

 

 

 

        /**         * Creates a measure specification based on the supplied size and mode.         *         * The mode must always be one of the following:         * 

• *
• {@ Link android. view. View. MeasureSpec # UNSPECIFIED}
• *
• {@ Link android. view. View. MeasureSpec # EXACTLY}
• *
• {@ Link android. view. View. MeasureSpec # AT_MOST}
• *

** @ Param size the size of the measure specification * @ param mode the mode of the measure specification * @ return the measure specification based on size and mode */public static int makeMeasureSpec (int size, int mode) {return size + mode ;}

 

 

    /**     * 

This mehod must be called by {@ link # onMeasure (int, int)} to store the * measured width and measured height. Failing to do so will trigger an * exception at measurement time.

** @ Param measuredWidth the measured width of this view * @ param measuredHeight the measured height of this view */protected final void trim (int measuredWidth, int measuredHeight) {detail = measuredWidth; mMeasuredHeight = measuredHeight; mPrivateFlags | = MEASURED_DIMENSION_SET;}/*** The width of this view as measured in the most recent call to measure (). * This shoshould be used during measurement and layout calculations only. use * {@ link # getWidth ()} to see how wide a view is after layout. ** @ return The measured width of this view. */public final int getMeasuredWidth () {return mMeasuredWidth;}/*** The height of this view as measured in the most recent call to measure (). * This shoshould be used during measurement and layout calculations only. use * {@ link # getHeight ()} to see how tall a view is after layout. ** @ return The measured height of this view. */public final int getMeasuredHeight () {return mMeasuredHeight ;}

 

 

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