Drawable的使用——TransitionDrawable

TransitionDrawable对应于标签，可以实现两个Drawable之间的淡入淡出效果

xml:

<transition xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/ic_sunny" />
    <item android:drawable="@drawable/ic_sunny_blue" />
transition>

布局

 <ImageView
                android:id="@+id/tv_transition"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:src="@drawable/bg_transition_drawable"
                android:text="TransitionDrawable" />

代码

    val textView = findViewById<ImageView>(R.id.tv_transition)
        var td: TransitionDrawable =
            textView.resources.getDrawable(R.drawable.bg_transition_drawable, null) as TransitionDrawable
        textView.setImageDrawable(td)
        btn_start.setOnClickListener {
            td.startTransition(1000)
        }
        btn_reverse.setOnClickListener {
            td.reverseTransition(1000)
        }

效果