ref.gif

package com.example.mvvmdemo

import android.animation.ObjectAnimator
import android.annotation.SuppressLint
import android.content.Context
import android.util.AttributeSet
import android.util.Log
import android.view.View
import android.widget.LinearLayout

class ExpandLinearLayout : LinearLayout{
    //是否展开，默认展开
    private var isOpen = true

    //第一个子view的高度，即收起保留高度
    private var firstChildHeight = 0

    //所有子view高度，即总高度
    private var allChildHeight = 0

    /**
     * 动画值改变的时候 请求重新布局
     */
    private var animPercent: Float = 0f
        set(value) {
            field = value
            requestLayout()
        }

    constructor(context: Context) : super(context) {
        initView()
    }

    constructor(context: Context, attributeSet: AttributeSet) : super(context, attributeSet) {
        initView()
    }

    constructor(context: Context, attributeSet: AttributeSet, defStyleAttr: Int) : super(
            context,
            attributeSet,
            defStyleAttr
    ) {
        initView()
    }

    private fun initView() {
        //横向的话 稍加修改计算宽度即可
        orientation = VERTICAL

        animPercent = 1f
        isOpen = true
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)

        //重置高度
        allChildHeight = 0
        firstChildHeight = 0

        if (childCount > 0) {

            //遍历计算高度
            for (index in 0 until childCount) {
                //这个地方实际使用中除了measuredHeight，以及margin等，也要计算在内
                val childView: View = getChildAt(index)
                val params: MarginLayoutParams = childView.layoutParams as MarginLayoutParams
                if (index == 0) {
                    firstChildHeight = childView.measuredHeight +params.topMargin  + params.bottomMargin  +this.paddingTop + this.paddingBottom
                    Log.i("firstChildHeight",firstChildHeight.toString());
                }
                //实际使用时或包括padding等
                allChildHeight += childView.measuredHeight + params.topMargin + params.bottomMargin

                //最后一条的时候 加上当前view自身的padding
                if (index == childCount - 1) {
                    allChildHeight += this.paddingTop + this.paddingBottom
                }
            }

            // 根据是否展开设置高度
            if (isOpen) {
                setMeasuredDimension(
                        widthMeasureSpec,
                        firstChildHeight + ((allChildHeight - firstChildHeight) * animPercent).toInt()
                )
            } else {
                setMeasuredDimension(
                        widthMeasureSpec,
                        allChildHeight - ((allChildHeight - firstChildHeight) * animPercent).toInt()
                )
            }
        }
    }

    fun toggle(): Boolean {
        isOpen = !isOpen
        startAnim()
        return isOpen
    }

    /**
     * 执行动画的时候 更改 animPercent 属性的值 即从0-1
     */
    @SuppressLint("AnimatorKeep")
    private fun startAnim() {
        //ofFloat，of xxxX 根据参数类型来确定
        //1，动画对象，即当前view。2.动画属性名。3，起始值。4，目标值。
        val animator = ObjectAnimator.ofFloat(this, "animPercent", 0f, 1f)
        animator.duration = 500
        animator.start()
    }
}

 <com.example.mvvmdemo.ExpandLinearLayout
            android:id="@+id/ell"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="#f5f5f5"
            android:orientation="vertical"
            android:padding="10dp"
            tools:ignore="MissingConstraints">

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:padding="10dp"
                android:text="@string/app_name"
                android:textSize="20sp" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:padding="10dp"
                android:text="@string/app_name"
                android:textSize="20sp" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:padding="10dp"
                android:text="@string/app_name"
                android:textSize="20sp" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:padding="10dp"
                android:text="@string/app_name"
                android:textSize="20sp" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:padding="10dp"
                android:text="@string/app_name"
                android:textSize="20sp" />

        </com.example.mvvmdemo.ExpandLinearLayout>

使用

 findViewById(R.id.ell).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                boolean toggle = ((ExpandLinearLayout)findViewById(R.id.ell)).toggle();
                //tv_tip.text = if (toggle) "收起" else "展开"
                startImageRotate( toggle);
            }
        });

如果放一个旋转的图标

 /**
     * 旋转箭头图标
     */
    private fun startImageRotate(imageView: ImageView, toggle: Boolean) {
        val tarRotate: Float = if (toggle) {
            0f
        } else {
            180f
        }

        imageView.apply {
            ObjectAnimator.ofFloat(this, "rotation", rotation, tarRotate).let {
                it.duration = 300
                it.start()
            }
        }
    }
}