<xml>
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" app:layout_behavior="@string/appbar_scrolling_view_behavior" tools:context="com.mycompany.helloworld.MainActivity" tools:showIn="@layout/activity_main"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello World!" /> </android.support.constraint.ConstraintLayout> </android.support.constraint.ConstraintLayout> 其中，wrap_content为强制扩充来显示textview中的内容 <MainActivity> package com.mycompany.helloworld; import android.os.Bundle; import android.support.design.widget.FloatingActionButton; import android.support.design.widget.Snackbar; import android.support.v7.app.AppCompatActivity; import android.support.v7.widget.Toolbar; import android.view.View; import android.view.Menu; import android.view.MenuItem; public class MainActivity extends AppCompatActivity {//写方法时继承自Activity @Override//伪代码，表示方法重写 protected void onCreate(Bundle savedInstanceState) {//Bundle savedInstanceState用于保存状态 super.onCreate(savedInstanceState); //调用Activity的onCreate方法,和Activity必须搭配使用 setContentView(R.layout.activity_main);//setContentView将Activity与xml可视化文件关联的代码 } }
