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));    }}