为什么 getMeasuredHeight() 和 getHeight() 的值会相等，又 Bug 了？

布局就是一个 ScrollView 包裹一个超长文章的 TextView ，超过屏幕显示了。

按网上所说， getHeight() 最大就是获取屏幕的高度，但是这里 getHeight() 却和 getMeasuredHeight() 的值相等，都超过我的屏幕高度 1280 了，和网上所说的不符啊。

代码也是最基础的，难道又 Bug 了，或者 getHeight() 和 getMeasuredHeight() 本来就相等？

Log 语句：

scrollView.getMeasuredHeight() + ":" + scrollView.getHeight() + ":" + scrollView.getChildAt(0).getMeasuredHeight() + ":" + scrollView.getChildAt(0).getHeight() + ":" + scrollView.getScrollY()

Log：

08-23 14:42:34.428 3282-3282/com.example.system.myapplication I/Tag: 1230:1230:2733:2733:1503
08-23 14:42:34.428 3282-3282/com.example.system.myapplication I/Tag: 底部
08-23 14:42:34.870 3282-3282/com.example.system.myapplication I/Tag: 1230:1230:2733:2733:1248
08-23 14:42:35.355 3282-3282/com.example.system.myapplication I/Tag: 1230:1230:2733:2733:916
08-23 14:42:35.909 3282-3282/com.example.system.myapplication I/Tag: 1230:1230:2733:2733:464
08-23 14:42:36.458 3282-3282/com.example.system.myapplication I/Tag: 1230:1230:2733:2733:0
08-23 14:42:36.458 3282-3282/com.example.system.myapplication I/Tag: 顶部
08-23 14:42:37.998 3282-3282/com.example.system.myapplication I/Tag: 1230:1230:2733:2733:0
08-23 14:42:37.998 3282-3282/com.example.system.myapplication I/Tag: 顶部
08-23 14:42:38.927 3282-3282/com.example.system.myapplication I/Tag: 1230:1230:2733:2733:484

MainActivity.java：

package com.example.system.myapplication;

import android.app.Activity;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ScrollView;
import android.widget.TextView;

public class MainActivity extends Activity implements View.OnTouchListener {
    private ScrollView scrollView;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);

        TextView textView = (TextView) findViewById(R.id.textView);
        textView.setText(getResources().getString(R.string.content));

        scrollView = (ScrollView) findViewById(R.id.scrollView);
        scrollView.setOnTouchListener(this);
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.i("Tag", scrollView.getMeasuredHeight() + ":" + scrollView.getHeight() + ":" + scrollView.getChildAt(0).getMeasuredHeight() + ":" + scrollView.getChildAt(0).getHeight() + ":" + scrollView.getScrollY());
                if (scrollView.getScrollY() == 0) {
                    Log.i("Tag", "顶部");
                }
                if (scrollView.getScrollY() + scrollView.getHeight() == scrollView.getChildAt(0).getHeight()) {
                    Log.i("Tag", "底部");
                }
                break;
            case MotionEvent.ACTION_MOVE:
                break;
            case MotionEvent.ACTION_UP:
                break;
        }
        return false;
    }
}

main_activity.xml：

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

    <ScrollView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/scrollView">
        <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="New Text"
                android:textSize="20sp"
                android:id="@+id/textView"/>
    </ScrollView>

</LinearLayout>