效果图：

代码：

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ValueAnimator;
import android.content.Context;
import android.text.TextUtils;
import android.util.AttributeSet;
import android.view.View;
import android.view.animation.DecelerateInterpolator;
import android.widget.LinearLayout;
import android.widget.TextView;

/**
 * Created by pengkv on 16/1/11.
 */
public class ExpandTextView extends TextView implements View.OnClickListener {

    private int mMaxCount;//记录文本框的最大行数
    private boolean isSinleLine = true;//是否是单行显示
    private boolean isFitst = true;//是否是第一次测量

    public ExpandTextView(Context context) {
        super(context);
        setOnClickListener(this);
    }

    public ExpandTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setOnClickListener(this);
    }

    public ExpandTextView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setOnClickListener(this);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (isFitst) {//如果是第一次测量，记录最大行数，测量后设置成单行
            mMaxCount = getLineCount();
            setEllipsize(TextUtils.TruncateAt.END);
            setSingleLine();
            isFitst = false;
        }
    }

    @Override
    public void onClick(View v) {

        ValueAnimator animator;
        final LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) getLayoutParams();
        if (isSinleLine) {//设置展开动画的位移
            setSingleLine(false);
            animator = ValueAnimator.ofInt(getLineHeight(), mMaxCount * getLineHeight());
        } else {//设置收缩动画的位移
            animator = ValueAnimator.ofInt(mMaxCount * getLineHeight(), getLineHeight());
        }
        //属性动画的用法
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                params.height = (int) animation.getAnimatedValue();
                setLayoutParams(params);
            }
        });
        animator.setInterpolator(new DecelerateInterpolator());
        animator.setDuration(300);
        animator.setTarget(this);
        animator.start();

        animator.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                super.onAnimationEnd(animation);
                if (!isSinleLine) {//在动画结束后设置成单行，避免效果异常
                    setSingleLine();
                }
                isSinleLine = !isSinleLine;
            }
        });
    }
}

XML使用：

//注意：不要在xml的view.ExpandTextView里面定义singleLine、ellipsize属性，否则会异常

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="10dp">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="10dp"
        android:text="@string/str1"
        android:textSize="18sp" />

    <view.ExpandTextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="10dp"
        android:text="@string/str2"
        android:textColor="#edd206"
        android:textSize="18sp" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/str3"
        android:textSize="18sp" />

</LinearLayout>

Tip：

代码中涉及到的属性动画建议参考这里。