public class PercentLayoutHelper extends Object
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:
ViewGroup.LayoutParams
subclass in your ViewGroup that implements
PercentLayoutHelper.PercentLayoutParams
.
LayoutParams(Context c, AttributeSet attrs)
constructor create an instance
of PercentLayoutHelper.PercentLayoutInfo
by calling
getPercentLayoutInfo(Context, AttributeSet)
. Return this
object from public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo()
method that you implemented for PercentLayoutHelper.PercentLayoutParams
interface.
ViewGroup.LayoutParams#setBaseAttributes(TypedArray, int, int)
with a single line implementation PercentLayoutHelper.fetchWidthAndHeight(this, a,
widthAttr, heightAttr);
ViewGroup.generateLayoutParams(AttributeSet)
to return
your LayoutParams.
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); } }
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(); }
Modifier and Type | Class and 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 and Description |
---|
PercentLayoutHelper(ViewGroup host) |
Modifier and Type | Method and 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(ViewGroup.LayoutParams params,
TypedArray array,
int widthAttr,
int heightAttr)
Helper method to be called from
ViewGroup.LayoutParams#setBaseAttributes override
that reads layout_width and layout_height attribute values without throwing an exception if
they aren't present. |
static PercentLayoutHelper.PercentLayoutInfo |
getPercentLayoutInfo(Context context,
AttributeSet attrs)
Constructs a PercentLayoutInfo from attributes associated with a View.
|
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.
|
public static void fetchWidthAndHeight(ViewGroup.LayoutParams params, TypedArray array, int widthAttr, int heightAttr)
ViewGroup.LayoutParams#setBaseAttributes
override
that reads layout_width and layout_height attribute values without throwing an exception if
they aren't present.public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec)
widthMeasureSpec
- Width MeasureSpec of the parent ViewGroup.heightMeasureSpec
- Height MeasureSpec of the parent ViewGroup.public static PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo(Context context, AttributeSet attrs)
LayoutParams(Context c, AttributeSet attrs)
constructor.public void restoreOriginalParams()
adjustChildren(int, int)
.public boolean handleMeasuredStateTooSmall()
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
.