Package com.batch.android.messaging.view.percent

Class PercentLayoutHelper

  • public class PercentLayoutHelper
extends java.lang.Object
    Helper for layouts that want to support percentage based dimensions.

    This class collects utility methods that are involved in extracting percentage based dimension attributes and applying them to ViewGroup's children. If you would like to implement a layout that supports percentage based dimensions, you need to take several steps:

    1. You need a ViewGroup.LayoutParams subclass in your ViewGroup that implements PercentLayoutHelper.PercentLayoutParams.
    2. In your LayoutParams(Context c, AttributeSet attrs) constructor create an instance of PercentLayoutHelper.PercentLayoutInfo. Return this object from public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() method that you implemented for PercentLayoutHelper.PercentLayoutParams interface.
    3. Override ViewGroup.LayoutParams.setBaseAttributes(TypedArray, int, int) with a single line implementation PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr);
    4. In your ViewGroup override ViewGroup.generateLayoutParams(AttributeSet) to return your LayoutParams.
    5. In your View.onMeasure(int, int) override, you need to implement following pattern: 
       protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);
 super.onMeasure(widthMeasureSpec, heightMeasureSpec);
 if (mHelper.handleMeasuredStateTooSmall()) {
 super.onMeasure(widthMeasureSpec, heightMeasureSpec);
 }
 }
    6. In your ViewGroup.onLayout(boolean, int, int, int, int) override, you need to implement following pattern: 
       protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
 super.onLayout(changed, left, top, right, bottom);
 mHelper.restoreOriginalParams();
 }

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      static class  PercentLayoutHelper.PercentLayoutInfo
      Container for information about percentage dimensions and margins.
      static interface  PercentLayoutHelper.PercentLayoutParams
      If a layout wants to support percentage based dimensions and use this helper class, its LayoutParams subclass must implement this interface.

    • Constructor Summary

      Constructors 
      Constructor Description
      PercentLayoutHelper​(android.view.ViewGroup host)  

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void adjustChildren​(int widthMeasureSpec, int heightMeasureSpec)
      Iterates over children and changes their width and height to one calculated from percentage values.
      static void fetchWidthAndHeight​(android.view.ViewGroup.LayoutParams params, android.content.res.TypedArray array, int widthAttr, int heightAttr)
      Helper method to be called from ViewGroup.LayoutParams.setBaseAttributes(android.content.res.TypedArray, int, int) override that reads layout_width and layout_height attribute values without throwing an exception if they aren't present.
      boolean handleMeasuredStateTooSmall()
      Iterates over children and checks if any of them would like to get more space than it received through the percentage dimension.
      void restoreOriginalParams()
      Iterates over children and restores their original dimensions that were changed for percentage values.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • PercentLayoutHelper

        public PercentLayoutHelper​(android.view.ViewGroup host)

    • Method Detail

      • fetchWidthAndHeight

        public static void fetchWidthAndHeight​(android.view.ViewGroup.LayoutParams params,
                                       android.content.res.TypedArray array,
                                       int widthAttr,
                                       int heightAttr)
        Helper method to be called from ViewGroup.LayoutParams.setBaseAttributes(android.content.res.TypedArray, int, int) override that reads layout_width and layout_height attribute values without throwing an exception if they aren't present.

      • adjustChildren

        public void adjustChildren​(int widthMeasureSpec,
                           int heightMeasureSpec)
        Iterates over children and changes their width and height to one calculated from percentage values.
        Parameters:
        widthMeasureSpec - Width MeasureSpec of the parent ViewGroup.
        heightMeasureSpec - Height MeasureSpec of the parent ViewGroup.

      • restoreOriginalParams

        public void restoreOriginalParams()
        Iterates over children and restores their original dimensions that were changed for percentage values. Calling this method only makes sense if you previously called adjustChildren(int, int).

      • handleMeasuredStateTooSmall

        public boolean handleMeasuredStateTooSmall()
        Iterates over children and checks if any of them would like to get more space than it received through the percentage dimension.

        If you are building a layout that supports percentage dimensions you are encouraged to take advantage of this method. The developer should be able to specify that a child should be remeasured by adding normal dimension attribute with wrap_content value. For example he might specify child's attributes as app:layout_widthPercent="60%p" and android:layout_width="wrap_content". In this case if the child receives too little space, it will be remeasured with width set to WRAP_CONTENT.

        Returns:
        True if the measure phase needs to be rerun because one of the children would like to receive more space.