android中如何实现mvc

android中如何实现mvc

用MVC进行重构,例:
Step1：抽取所有界面元件的声明和定义，整合到单独一个函数findViews()中；
// 声明
private Button button_calc;
private EditText field_height;
private EditText field_weight;
private TextView view_result;
private TextView view_suggest;

// 定义
private void findViews() {
button_calc = (Button) findViewById(R.id.submit);
field_height = (EditText) findViewById(R.id.height);
field_weight = (EditText) findViewById(R.id.weight);
view_result = (TextView) findViewById(R.id.result);
view_suggest = (TextView) findViewById(R.id.suggest);
}
此部分即是MVC中的V：View视图。
Step2：抽取程序的逻辑（即界面元件的处理逻辑），整合到函数setListensers()中；
//Listen for button clicks
private void setListensers() {
button_calc.setOnClickListener(calcBMI);
}
此部分即是MVC中的C：Controller控制器。
接着，onCreate()就显得非常简洁、明了了：
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

findViews();
setListensers();
}
Step3：修改按钮监听器calcBMI中相应的部分（主要是变量已经在视图部分定义了）；
private OnClickListener calcBMI = new OnClickListener() {
@Override
public void onClick(View v) {
DecimalFormat nf = new DecimalFormat("0.00");

double height = Double.parseDouble(field_height.getText().toString()) / 100;
double weight = Double.parseDouble(field_weight.getText().toString());
double BMI = weight / (height * height);

// Present result
view_result.setText("Your BMI is " + nf.format(BMI));

// Give health advice
if (BMI > 25) {
view_suggest.setText(R.string.advice_heavy);
} else if (BMI < 20) {
view_suggest.setText(R.string.advice_light);
} else {
view_suggest.setText(R.string.advice_average);
}
}
};
Step4：修剪一下“细枝末节”；
1) calcBMI的修改：
private OnClickListener calcBMI = new OnClickListener() {
……
}
改成如下：
private Button.OnClickListener calcBMI = new Button.OnClickListener() {
……
}
gasolin的解释是：
同样是「calcBMI」 函式，在完整程式中，改将「calcBMI」 函式从原本的「OnClickListener」宣告成 「Button.OnClickListener」。这个改变有什麼差别呢？
阅读原本的程式码，在汇入(import)的部分可以看到，「OnClickListener」是来自於「android.view.View.OnClickListener」函式：
import android.view.View.OnClickListener;
改成 「Button.OnClickListener」後，「Button.OnClickListener」就变成来自於「android.widget.Button」中的「OnClickListener」函式，在查阅程式时，整个「Button」与「OnClickListener」之间的关系变得更清晰。
2) 字符串统一引用XML中的描述符：
//Present result
view_result.setText("Your BMI is " + nf.format(BMI));
改成如下：
//Present result
view_result.setText(getText(R.string.bmi_result) + nf.format(BMI));

总之，此重构的目的无非是使程序的脉络更加清晰，即让人一眼望去，就能很容易地分辨出界面（View）应该写在哪里，程序逻辑（Controller）应该写在哪里，最终使维护和扩展代码变得更加容易！
重构前的代码Bmi.java：
package com.demo.android.bmi;

import java.text.DecimalFormat;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class Bmi extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

// Listen for button clicks
Button button = (Button) findViewById(R.id.submit);
button.setOnClickListener(calcBMI);
}

private OnClickListener calcBMI = new OnClickListener() {
@Override
public void onClick(View v) {
DecimalFormat nf = new DecimalFormat("0.00");
EditText fieldheight = (EditText) findViewById(R.id.height);
EditText fieldweight = (EditText) findViewById(R.id.weight);

double height = Double.parseDouble(fieldheight.getText().toString()) / 100;
double weight = Double.parseDouble(fieldweight.getText().toString());
double BMI = weight / (height * height);

TextView result = (TextView) findViewById(R.id.result);
result.setText("Your BMI is " + nf.format(BMI));

// Give health advice
TextView fieldsuggest = (TextView) findViewById(R.id.suggest);
if (BMI > 25) {
fieldsuggest.setText(R.string.advice_heavy);
} else if (BMI < 20) {
fieldsuggest.setText(R.string.advice_light);
} else {
fieldsuggest.setText(R.string.advice_average);
}
}
};
}

2) 重构后的代码Bmi.java：
package com.demo.android.bmi;

import java.text.DecimalFormat;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class Bmi extends Activity {

private Button button_calc;
private EditText field_height;
private EditText field_weight;
private TextView view_result;
private TextView view_suggest;


@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

findViews();
setListensers();
}

// 定义
private void findViews() {
button_calc = (Button) findViewById(R.id.submit);
field_height = (EditText) findViewById(R.id.height);
field_weight = (EditText) findViewById(R.id.weight);
view_result = (TextView) findViewById(R.id.result);
view_suggest = (TextView) findViewById(R.id.suggest);
}

// Listen for button clicks
private void setListeners() {
calcbutton.setOnClickListener(calcBMI);
}

private Button.OnClickListener calcBMI = new Button.OnClickListener() {
public void onClick(View v) {
DecimalFormat nf = new DecimalFormat("0.0");
double height = Double.parseDouble(field_height.getText().toString()) / 100;
double weight = Double.parseDouble(field_weight.getText().toString());
double BMI = weight / (height * height);

// Present result
view_result.setText(getText(R.string.bmi_result) + nf.format(BMI));

// Give health advice
if (BMI > 25) {
view_suggest.setText(R.string.advice_heavy);
} else if (BMI < 20) {
view_suggest.setText(R.string.advice_light);
} else {
view_suggest.setText(R.string.advice_average);
}
}
};
}