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What is a StateListDrawable?
Let’s say you have a View like a Button. You want to set a background to the button, you use
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android:background=”@drawable/ic_assignment_returned_black_24dp” |
But what can you do when you want to set a different background while the button is pressed or maybe when the button is not focused anymore.
My first solution for this problem was to extend a View class and override the setPressed() method to set the specific drawables.
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class MyToggleButton : android.support.v7.widget.AppCompatButton { constructor(context: Context) : super(context) {} constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {} constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int) : super(context, attrs, defStyleAttr) { } override fun setPressed(pressed: Boolean) { if (pressed) { background = resources.getDrawable(R.drawable.ic_assignment_turned_in_black_24dp) } else { background = resources.getDrawable(R.drawable.ic_assignment_returned_black_24dp) } } } |
In the fragment where i used the button I then called the method inside a onTouchListener()
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btn2.setOnTouchListener { v, event -> when { event.action == MotionEvent.ACTION_DOWN -> btn2.isPressed=true event.action == MotionEvent.ACTION_UP -> btn2.isPressed=false } true } |
This process can be simplified with StateListDrawables.
How do they work?
You just create a new xml file e.g. button_selector.xml inside your drawables folder.
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<?xml version="1.0" encoding="utf-8"?> <selector xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto"> <item android:drawable="@drawable/ic_assignment_turned_in_black_24dp" android:state_pressed="true"/> <item android:drawable="@drawable/ic_assignment_returned_black_24dp"/> </selector> |
This selector will do the same like my custom view. The drawable from the item with android:state_pressed=”true” will be used when the button is pressed. You can use StateListDrawables also for other attributes like textColor. Android will use the item without a state as the default one.
Here is a list of all states that are available:
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android:state_pressed=["true" | "false"] android:state_focused=["true" | "false"] android:state_hovered=["true" | "false"] android:state_selected=["true" | "false"] android:state_checkable=["true" | "false"] android:state_checked=["true" | "false"] android:state_enabled=["true" | "false"] android:state_activated=["true" | "false"] android:state_window_focused=["true" | "false"] |
How to apply the selector?
You just use it like any other drawable inside your layout file
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android:background="@drawable/button_selector" |
Android will set the attributes when the view is in the specified state
And that’s it. Now you can apply this selector to any of your Views.
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