android使用全局变量的两种方法

     在我们使用android编写程序的时候，少不了想利用全局变量，但是面向对象语言和过程语言区别很大，不再是include就可以的。这里我写了使用全局变量的两种方法：

 

1.使用application来保存全局变量                                                             

这里没有太多理论性的东西，无非就是一些实际操作。

1.1定义Data类继承Application Data.class

import android.app.Application;public class Data extends Application{private String b;public String getB(){return this.b;}public void setB(String c){this.b= c;}@Overridepublic void onCreate(){b = "hello";super.onCreate();}}

1.2在manifest.xml中声明application

android:name="com.animator1.Data" >

1.3创建两个Activity

MainActivity.class

public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);Button btn = (Button) this.findViewById(R.id.button1);final TextView txtview = (TextView) this.findViewById(R.id.main);final Data app = (Data)getApplication();txtview.setText(app.getB());btn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubapp.setB("no_hello");txtview.setText(app.getB());Intent intent = new Intent(MainActivity.this, secondActivity.class);startActivity(intent);}});}}

secondActivity.class

public class secondActivity extends Activity{@Overrideprotected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.second);Button btn = (Button) this.findViewById(R.id.button2);final TextView txtview = (TextView) this.findViewById(R.id.second);final Data app = (Data)getApplication();txtview.setText(app.getB());btn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubapp.setB("hello");txtview.setText(app.getB());Intent intent = new Intent(secondActivity.this, MainActivity.class);startActivity(intent);}});}}

1.4运行程序
   

说明：程序首先进入MainActivity.class中，获取Data中变量b的值，显示图1所示的界面hello，单击button后app.setB("no_hello")， 修改变量b的值。

           跳转到secondActivity.class，获取Data中变量b的值，显示图2所示的界面no_hello，单击button后app.setB("hello")， 修改变量b的值。

           跳转回MainActivity.class……  循环

2.使用普通的类Data.class来保存全局变量                                                             

方法和上面差不多。

1.1 定义Data.class

public class Data{private static String a ="feiyangxiaomi";public static String getA() {return a;}public static void setA(String a) {Data.a = a;}}

1.2创建两个Activity

MainActivity.class

public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);Button btn = (Button) this.findViewById(R.id.button1);final TextView txtview = (TextView) this.findViewById(R.id.main);txtview.setText(Data.getA());btn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubData.setA("no_feiyangxiaomi");Intent intent = new Intent(MainActivity.this, secondActivity.class);startActivity(intent);}});}}

secondActivity.class

public class secondActivity extends Activity{@Overrideprotected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.second);Button btn = (Button) this.findViewById(R.id.button2);final TextView txtview = (TextView) this.findViewById(R.id.second);txtview.setText(Data.getA());btn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubData.setA("feiyangxiaomi");Intent intent = new Intent(secondActivity.this, MainActivity.class);startActivity(intent);}});}}

1.3运行程序
                     

说明：程序首先进入MainActivity.class中，获取Data中变量b的值，显示图1所示的界面feiyangxiaomi，单击button后app.setB("no_feiyangxiaomi")， 修改变量b的值。

           跳转到secondActivity.class，获取Data中变量b的值，显示图2所示的界面no_feiyangxiaomi，单击button后app.setB("feiyangxiaomi")， 修改变量b的值。

           跳转回MainActivity.class……  循环

3.总结                                                                                        

    两种方法我测试的都可以的，大多数人应该更会偏向于第一种，毕竟Application是android专门提供的应用入口，并且运行周期贯穿整个程序运行。