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;
	}
	@Override
	public 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 {

	@Override
	protected 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() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				app.setB("no_hello");
				txtview.setText(app.getB());
				Intent intent = new Intent(MainActivity.this, secondActivity.class);
				startActivity(intent);
			}
		});
	}
}

secondActivity.class

public class secondActivity extends Activity{
	@Override
	protected 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() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub				
				app.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 {

	@Override
	protected 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() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				Data.setA("no_feiyangxiaomi");
				Intent intent = new Intent(MainActivity.this, secondActivity.class);
				startActivity(intent);
			}
		});
	}
}

secondActivity.class

public class secondActivity extends Activity{
	@Override
	protected 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() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub				
				Data.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。