SJ64 JUST JAVA 认识变量

订咖啡App

在Android Studio 中 可以通过ctrl + alt + L 格式化代码格式

认识活动——activity

显示视图与交互的界面，是个java文件

Button

onClick属性

android:onClick="submitOrder"//当按下按钮时会去调用submitOrder方法

<Button//
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="16dp"
    android:text="Order"
    android:textAllCaps="true"
    android:onClick="submitOrder"/>

public void submitOrder(View view) {
    int numberOfCoffees = 2;
    display(numberOfCoffees);
    displayPrice(numberOfCoffees * 5);
}

声明变量

【变量类型】 +【变量名】= 【变量值】;

int 整形数据

如 int numberOfCoffees = 2;

变量作用域

如果一个变量是在方法中被声明的，它只能在这个方法的作用域内被使用

Debug

1. 运用DDMS查看错误日志
2. 添加断点，然后用debug模式

activity_main.xml

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.clixin.justjava.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:text="Quantity"
        android:textAllCaps="true"
        android:textAppearance="?android:textAppearanceLarge"
        android:textColor="#344567" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <Button
            android:layout_width="48dp"
            android:layout_height="48dp"
            android:text="+"
            android:layout_marginRight="16dp"
            android:onClick="increment"/>

        <TextView
            android:id="@+id/quantity_text_view"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="0"
                android:textAppearance="?android:textAppearanceLarge" />

        <Button
            android:layout_width="48dp"
            android:layout_height="48dp"
            android:layout_marginLeft="16dp"
            android:text="-"
            android:onClick="decrement"/>

    </LinearLayout>


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:layout_marginTop="16dp"
        android:text="Price"
        android:textAllCaps="true"
        android:textAppearance="?android:textAppearanceLarge"
        android:textColor="#344567" />

    <TextView
        android:id="@+id/price_text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="￥10.0"
        android:textAppearance="?android:textAppearanceLarge" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Order"
        android:textAllCaps="true"
        android:textAppearance="?android:textAppearanceLarge"
        android:onClick="submitOrder"/>

</LinearLayout>

MainActivity.java

package com.example.clixin.justjava;

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.TextView;

import java.text.NumberFormat;

public class MainActivity extends ActionBarActivity {

    int quantity = 0;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void submitOrder(View view) {
        display(quantity);
        displayPrice(quantity * 5);
    }

    public void increment(View view) {
        quantity = quantity + 1;
        display(quantity);

    }

    public void decrement(View view) {
        quantity = quantity - 1;
        display(quantity);

    }

    private void display (int number) {
        TextView quantityTextView = (TextView)findViewById(R.id.quantity_text_view);
        quantityTextView.setText("" + number);
    }
    private void displayPrice(int number) {
        TextView priceTextView = (TextView)findViewById(R.id.price_text_view);
        priceTextView.setText(NumberFormat.getCurrencyInstance().format(number));
    }
}

Screenshot_2016-04-22-18-56-59.png