一个一个组件的实习过来。

package com.tw.flag.ch02_button;

import android.content.Context;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Vibrator;
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.text.Editable;
import android.text.TextWatcher;
import android.view.MotionEvent;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioGroup;
import android.widget.TextView;

import java.util.Random;

public class MainActivity extends AppCompatActivity
    implements RadioGroup.OnCheckedChangeListener, TextWatcher{
    RadioGroup unit;
    EditText value;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        unit = (RadioGroup) findViewById(R.id.unit);
        unit.setOnCheckedChangeListener(this);
        value = (EditText) findViewById(R.id.value);
        value.addTextChangedListener(this);
    }

    @Override
    public void onCheckedChanged(RadioGroup group, int checkedId) {
        calc();

    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {

    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {

    }

    @Override
    public void afterTextChanged(Editable s) {
        calc();

    }

    protected void calc() {
        TextView degF = (TextView)findViewById(R.id.degF);
        TextView degC = (TextView)findViewById(R.id.degC);
        double f, c;

        if (unit.getCheckedRadioButtonId() == R.id.unitF) {
            f = Double.parseDouble(value.getText().toString());
            c = (f - 32) * 5/9;
        } else {
            c = Double.parseDouble(value.getText().toString());
            f = c * 9/5 + 32;
        }
        degC.setText(String.format("%.1f", c) +
            getResources().getString(R.string.charC));
        degF.setText(String.format("%.1f", f) +
                getResources().getString(R.string.charF));
    }
}