Android View measure（三）常用方法

Android View measure（三）常用方法

 

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 parentHeightMeasureSpec, int heightUsed) {// 1 類型轉換        final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();// 2 getChildMeasureSpec方法        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);    }

 

此方法針對第一個參數傳遞的子視圖進行Measure操作。
1. 傳遞的子視圖LayoutParams必須是或者繼承自MarginLayoutParams，否者會拋出轉換異常

    /**     * 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方法        final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,                mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin                        + widthUsed, lp.width);}

 

調用此方法處，看看這三個參數的具體含義。
1. spec ： 此視圖要求的規格 【parentWidthMeasureSpec】
2. padding ： 當前ViewGroup視圖的padding值與傳入子視圖的margin值 【mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin + widthUsed】？widthUsed
3. childDimension : 傳入參數的視圖，期望展示多大【lp.width】

** 舉一個例子

擴充：MeasureSpec方法與拼接方式

 

 

 

    /**     * 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 setMeasuredDimension(int measuredWidth, int measuredHeight) { mMeasuredWidth = measuredWidth; mMeasuredHeight = measuredHeight; mPrivateFlags |= MEASURED_DIMENSION_SET; } /** * The width of this view as measured in the most recent call to measure(). * This should 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 should 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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