PercentLayoutHelper
open classPercentLayoutHelper
kotlin.Any | |
↳ | androidx.percentlayout.widget.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:
- You need a
ViewGroup.LayoutParams
subclass in your ViewGroup that implementsPercentLayoutHelper.PercentLayoutParams
. - In your
LayoutParams(Context c, AttributeSet attrs)
constructor create an instance ofPercentLayoutHelper.PercentLayoutInfo
by callingPercentLayoutHelper#getPercentLayoutInfo(Context, AttributeSet)
. Return this object frompublic PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo()
method that you implemented forPercentLayoutHelper.PercentLayoutParams
interface. - Override
ViewGroup.LayoutParams#setBaseAttributes(TypedArray, int, int)
with a single line implementationPercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr);
- In your ViewGroup override
ViewGroup#generateLayoutParams(AttributeSet)
to return your LayoutParams. - In your
ViewGroup#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); } }
- 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(); }
Summary
Nested classes | |
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open |
Container for information about percentage dimensions and margins. |
abstract |
If a layout wants to support percentage based dimensions and use this helper class, its |
Public constructors | |
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Public methods | |
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open Unit |
adjustChildren(widthMeasureSpec: Int, heightMeasureSpec: Int) Iterates over children and changes their width and height to one calculated from percentage values. |
open static Unit |
fetchWidthAndHeight(params: LayoutParams!, array: TypedArray!, widthAttr: Int, heightAttr: Int) Helper method to be called from |
open static PercentLayoutHelper.PercentLayoutInfo! |
getPercentLayoutInfo(context: Context!, attrs: AttributeSet!) Constructs a PercentLayoutInfo from attributes associated with a View. |
open Boolean |
Iterates over children and checks if any of them would like to get more space than it received through the percentage dimension. |
open Unit |
Iterates over children and restores their original dimensions that were changed for percentage values. |
Public constructors
<init>
PercentLayoutHelper(@NonNull host: ViewGroup)
Public methods
adjustChildren
open fun adjustChildren(
widthMeasureSpec: Int,
heightMeasureSpec: Int
): Unit
Iterates over children and changes their width and height to one calculated from percentage values.
Parameters | |
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widthMeasureSpec |
Int: Width MeasureSpec of the parent ViewGroup. |
heightMeasureSpec |
Int: Height MeasureSpec of the parent ViewGroup. |
fetchWidthAndHeight
open static fun fetchWidthAndHeight(
params: LayoutParams!,
array: TypedArray!,
widthAttr: Int,
heightAttr: Int
): Unit
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.
getPercentLayoutInfo
open static fun getPercentLayoutInfo(
context: Context!,
attrs: AttributeSet!
): PercentLayoutHelper.PercentLayoutInfo!
Constructs a PercentLayoutInfo from attributes associated with a View. Call this method from LayoutParams(Context c, AttributeSet attrs)
constructor.
handleMeasuredStateTooSmall
open fun handleMeasuredStateTooSmall(): Boolean
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
.
Return | |
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Boolean |
True if the measure phase needs to be rerun because one of the children would like to receive more space. |
restoreOriginalParams
open fun restoreOriginalParams(): Unit
Iterates over children and restores their original dimensions that were changed for percentage values. Calling this method only makes sense if you previously called PercentLayoutHelper#adjustChildren(int, int)
.