Scala Relative Layout Traits

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Cower	Created : 25 August 2013 Edited : 25 August 2013 System : Android Language : Other Scala Relative Layout Traits Some traits and an object to make working with Android's relative layout parameters easier, provided you're using Scala.
This was mostly intended as an experiment to see if I could make working with view layout in Scala simpler than using Android's godawful XML resources (which have their uses, but are a huge pain in the neck for a lot of reasons). Basically, if you need to create a subview of a relative layout in Android, you're probably already screaming in pain because Java is terrible and Android is heavily in favor of doing things the Java way — meaning long-winded and needlessly complicated. If you need to do that and don't want to suffer, 1) you're already using Scala, so that's a step, and 2) you can use this to write out stuff like the following: val layout = new RelativeLayout(activity) val button = new Button(activity) with RelativeLayoutHelper val text = new EditText(activity) with RelativeLayoutHelper button.setText("Hello, Boof") text alignTopWithParent() text alignStartWithParent() text alignEndBefore button text.topMargin = 10 button alignEndWithParent() button alignBaselineWith text layout.addView(button) layout.addView(text) --v That will net you a text view with a button to its side, both baseline-aligned, and so on. It's quite a bit more readable than XML. I might also just build up something to generate XML from far-more-readable Scala (or do it in Ruby), so that way you can use the same language for both runtime and compile-time layout. For example: Anyway, source is below. It's all documented. Should be pretty clear what it does, since it's not doing anything really weird — all the magical stuff is just Scala allowing me to have infix methods and such (postfix methods are also allowed but disabled by default because it's really easy to abuse and doesn't really contribute anything, so I don't recommend enabling it). Basically, the code's all really simple. package net.spifftastic.ui import android.widget.RelativeLayout import android.view.{View, ViewGroup} import android.widget.RelativeLayout.LayoutParams import android.util.Log /** * Object used to generate relatively/moderately/vaguely unique ids for views. Calling either * apply or idOf will generate an id for a view that does not already have one. / object ViewId { /* * The last "unique" view id "generated." In fact is just a counter. Should be obvious. * * @note There is no particular reason for the counter beginning at `1 << 18`, * the choice is arbitrary. View ids do not have to be unique across all views, * or even in the same hierarchy, so this is merely to try to reduce conflicts with any * view id constants -- that is, a view id generated by uniqueId must always be less than * `1 << 18`, meaning you have the larger subset of 31 bits to play with (as view ids * must be positive integers). / private[this] var _lastViewId = 1 << 18 /* * Returns a view id not previously returned by uniqueId, assuming you have not allocated * enough ids to cause the counter to both overflow and wrap around to its initial value. * @return a view id not previously returned by uniqueId. Assuming nothing weird happened. The * returned id will always be a positive integer greater than or equal to `1 << 18`. / def uniqueId = this.synchronized { _lastViewId += 1 if (_lastViewId < 0) _lastViewId = 1 << 18 // loop around _lastViewId } /* * Returns the view id of a view. If the view has no id, one is generated using uniqueId and * assigned to the view first. * @param view The view to get the id of. * @return the id of the view. / def idOf(view: View): Int = { val viewId = view.getId if (viewId == View.NO_ID) { val id = uniqueId view.setId(id) id } else { viewId } } } /* * Trait that simply requires `getId: Int` and `setId(id: Int): Unit` be implemented. All * View instances satisfy this requirement. / trait ViewTraits { /* * Gets the view's id. * @return the view's id or NO_ID if none is set. / def getId: Int /* * Sets the view's id. * @param id / def setId(id: Int): Unit /* * Sets the current layout parameters. * @param params the layout params, or null if none are to be set. / def setLayoutParams(params: ViewGroup.LayoutParams): Unit /* * Gets the current layout parameters. * @return the view's layout parameters, or null if none are set. / def getLayoutParams: ViewGroup.LayoutParams } /* * A trait to be applied to newly allocated views that guarantees the view is given a unique view * id generated by ViewId on initialization. Afterward, the view may not have a unique id. * * @note the id assigned may not be unique among all views in the view hierarchy, * but simply unique among those generated by ViewId. / trait UniqueViewId extends ViewTraits { import ViewId.uniqueId // Generate the view's id only if it needs one. if (getId == View.NO_ID) setId(uniqueId) } /* * Provides helper methods for building a view's relative layout parameters. It assumes that the * view this is included with already has relative layout parameters -- if it doesn't, * all alignment methods are no-ops. * * @example * {{{ * val button: Button = new Button with RelativeLayoutHelper with UniqueViewId * button.relativeLayoutParams = new RelativeLayout.LayoutParams(WRAP_CONTENT, WRAP_CONTENT) * button alignLeftWithParent * button alignRightOf otherView * button alignBelow yetAnotherView * }}} / trait RelativeLayoutHelper extends ViewTraits { import RelativeLayout._ import ViewId.idOf import ViewGroup.LayoutParams.WRAP_CONTENT getLayoutParams match { case null => setLayoutParams(new LayoutParams(WRAP_CONTENT, WRAP_CONTENT)) case params: LayoutParams => // nop case params: ViewGroup.LayoutParams => setLayoutParams(new LayoutParams(params.width, params.height)) } /* * Wrapper around getLayoutParams that returns an option with relative layout parameters. If * the current layout parameters are not relative layout parameters, it returns none. * @return Some(RelativeLayout.LayoutParams) or None / def relativeLayoutParams: Option[LayoutParams] = getLayoutParams match { case null => None case params: LayoutParams => Some(params) } /* Wrapper around setLayoutParams. Simply sets the layout parameters to those given. / def relativeLayoutParams_=(params: LayoutParams): Unit = setLayoutParams(params) /* Aligns this view to the left of the given view. / def alignLeftOf(other: View): Unit = relativeLayoutParams.foreach(_.addRule(LEFT_OF, idOf(other))) /* Aligns this view with the left of another view. / def alignLeftWith(other: View): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_LEFT, idOf(other))) /* Aligns this view with the left of its parent. / def alignLeftWithParent(): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_PARENT_LEFT)) /* Aligns this view to the right of the given view. / def alignRightOf(other: View): Unit = relativeLayoutParams.foreach(_.addRule(RIGHT_OF, idOf(other))) /* Aligns this view with the right of another view. / def alignRightWith(other: View): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_RIGHT, idOf(other))) /* Aligns this view with the right of its parent. / def alignRightWithParent(): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_PARENT_RIGHT)) /* Aligns this view above the given view. (this.top == other.bottom) / def alignAbove(other: View): Unit = relativeLayoutParams.foreach(_.addRule(ABOVE, idOf(other))) /* Aligns this view with the top of another view. / def alignTopWith(other: View): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_TOP, idOf(other))) /* Aligns this view with the top of its parent. / def alignTopWithParent(): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_PARENT_TOP)) /* Aligns this view below the given view. / def alignBelow(other: View): Unit = relativeLayoutParams.foreach(_.addRule(BELOW, idOf(other))) /* Aligns this view with the bottom of another view. / def alignBottomWith(other: View): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_BOTTOM, idOf(other))) /* Aligns this view with the bottom of its parent. / def alignBottomWithParent(): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_PARENT_BOTTOM)) /* Aligns this view with the baseline of another view. / def alignBaselineWith(other: View): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_BASELINE, idOf(other))) /* Aligns this view in the horizontal center of its parent. / def alignCenterHorizontally(): Unit = relativeLayoutParams.foreach(_.addRule(CENTER_HORIZONTAL)) /* Aligns this view vertical center of its parent. / def alignCenterVertically(): Unit = relativeLayoutParams.foreach(_.addRule(CENTER_HORIZONTAL)) /* Aligns this view in the center of its parent. / def alignCenterInParent(): Unit = relativeLayoutParams.foreach(_.addRule(CENTER_HORIZONTAL)) def leftMargin: Option[Int] = for (params <- relativeLayoutParams) yield params.leftMargin def leftMargin_=(margin: Int): Unit = relativeLayoutParams.foreach(_.leftMargin = margin) def rightMargin: Option[Int] = for (params <- relativeLayoutParams) yield params.rightMargin def rightMargin_=(margin: Int): Unit = relativeLayoutParams.foreach(_.rightMargin = margin) def topMargin: Option[Int] = for (params <- relativeLayoutParams) yield params.topMargin def topMargin_=(margin: Int): Unit = relativeLayoutParams.foreach(_.topMargin = margin) def bottomMargin: Option[Int] = for (params <- relativeLayoutParams) yield params.bottomMargin def bottomMargin_=(margin: Int): Unit = relativeLayoutParams.foreach(_.bottomMargin = margin) // Comment out the following methods for target API level < 17 /* Aligns the end of this view to the start of another view. / def alignEndBefore(other: View): Unit = relativeLayoutParams.foreach(_.addRule(START_OF, idOf(other))) /* Aligns this view's end with the end of another view. / def alignToEndOf(other: View): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_END, idOf(other))) /* Aligns this view's end with the end of its parent. / def alignEndWithParent(): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_PARENT_END)) /* Aligns the start of this view to the end of the given view. / def alignStartAfter(other: View): Unit = relativeLayoutParams.foreach(_.addRule(END_OF, idOf(other))) /* Aligns this view's start with the start of another view. / def alignToStartOf(other: View): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_START, idOf(other))) /* Aligns this view's start with the start of its parent. / def alignStartWithParent(): Unit = relativeLayoutParams.foreach(_.addRule(ALIGN_PARENT_START)) } /* * Helper object that implements apply, allowing callers to provide a view and a closure or * function that sets up view bindings, regardless of whether the view implements * RelativeLayoutHelper. * * @example * {{{ * buildRelativeLayoutParams(view) { v => * v alignLeftOf otherView * v centerVertically() * } * }}} / object buildRelativeLayoutParams { val TAG = "buildRelativeLayoutParams" /* * Wraps a view and implements methods needed by RelativeLayoutHelper, forwarding to the view. * @param view The view to wrap. / private class LayoutViewWrapper(private[this] val view: View) extends RelativeLayoutHelper { def getId: Int = view.getId def setId(id: Int): Unit = view.setId(id) def setLayoutParams(params: ViewGroup.LayoutParams): Unit = view.setLayoutParams(params) def getLayoutParams: ViewGroup.LayoutParams = view.getLayoutParams } /* * Wraps a view in a helper object that implements RelativeLayoutHelper and passes said object * to a build function to set up. Once the parameters are set and the builder is done, * it re-sets the view's layout parameters. If the view already implements RelativeLayoutHelper, * no wrapper is necessary and the input view will be passed directly to the build function. * * @param view The view to build layout parameters for. * @param build The builder function called with the view wrapper. */ def apply(view: View)(build: (RelativeLayoutHelper => Unit)): Unit = { import ViewGroup.LayoutParams.WRAP_CONTENT view.getLayoutParams match { case params: LayoutParams => { Log.d(TAG, "Layout parameters already relative") }// nop case other: ViewGroup.LayoutParams => { Log.d(TAG, "Converting existing layout parameters") view.setLayoutParams(new LayoutParams(other.width, other.height)) } case _ => { Log.d(TAG, "Creating new layout parameters") view.setLayoutParams(new LayoutParams(WRAP_CONTENT, WRAP_CONTENT)) } } Log.d(TAG, "Passing view to builder") build(view match { case withoutWrapper: RelativeLayoutHelper => withoutWrapper case _ => new LayoutViewWrapper(view) }) Log.d(TAG, "Re-setting layout parameters") // Rather than duplicate what setLayoutParams does, just re-set it to the same thing. Doesn't // look insane at all. Also, you might be thinking, why not cache the layout params above // since they're checked? Reason: you might be a horrible person and change them // mid-building, and wouldn't that be silly. WOULDN'T THAT BE SILLY. view.setLayoutParams(view.getLayoutParams) } } --v

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Scala Relative Layout Traits

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