android第一行代码随笔

实现toast和打印功能：

layout：

<?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"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="110dp"
        android:layout_height="52dp"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.376"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.41000003" />

    <Button
        android:id="@+id/button_1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button 1"
        />

</android.support.constraint.ConstraintLayout>

java源码:

package com.example.bwcheng.myapplication;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);//重写父类的方法并调用
        setContentView(R.layout.activity_main);//主Activity中加载布局
        Log.d("MainActivity", "onCerate execute");
        Button button1 = (Button) findViewById(R.id.button_1);//定义触发点
        button1.setOnClickListener(new View.OnClickListener() {//注册监听器
            @Override
            public void onClick(View v) {//点击事件         

              Toast.makeText(MainActivity.this, "you click button", Toast.LENGTH_SHORT).show();

            }
        });
    }

}