PercentLayoutHelper

public class PercentLayoutHelper

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 by calling getPercentLayoutInfo. Return this object from public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() method that you implemented for PercentLayoutHelper.PercentLayoutParams interface.
3. Override setBaseAttributes with a single line implementation PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr);
4. In your ViewGroup override generateLayoutParams to return your LayoutParams.
5. In your onMeasure 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 onLayout 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();
   }
   

Summary

public PercentLayoutHelper(@NonNull ViewGroup host)

public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec)

public static void fetchWidthAndHeight(
    ViewGroup.LayoutParams params,
    TypedArray array,
    int widthAttr,
    int heightAttr
)

public static PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo(Context context, AttributeSet attrs)

public boolean handleMeasuredStateTooSmall()

public void restoreOriginalParams()