[转]android使用全局变量的两种方法

本文转自：http://blog.csdn.net/feiyangxiaomi/article/details/9966215

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

1. import android.app.Application;
2. publicclass Data extends Application{
3. private String b;
4. public String getB(){
5. returnthis.b;
6. }
7. publicvoid setB(String c){
8. this.b= c;
9. }
10. @Override
11. publicvoid onCreate(){
12. b = "hello";
13. super.onCreate();
14. }
15. }

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

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

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

1.3创建两个Activity

MainActivity.class

1. publicclass MainActivity extends Activity {
2. @Override
3. protectedvoid onCreate(Bundle savedInstanceState) {
4. super.onCreate(savedInstanceState);
5. setContentView(R.layout.main);
6. Button btn = (Button) this.findViewById(R.id.button1);
7. final TextView txtview = (TextView) this.findViewById(R.id.main);
8. final Data app = (Data)getApplication();
9. txtview.setText(app.getB());
10. btn.setOnClickListener(new View.OnClickListener() {
11. @Override
12. publicvoid onClick(View v) {
13. // TODO Auto-generated method stub
14. app.setB("no_hello");
15. txtview.setText(app.getB());
16. Intent intent = new Intent(MainActivity.this, secondActivity.class);
17. startActivity(intent);
18. }
19. });
20. }
21. }

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

1. publicclass secondActivity extends Activity{
2. @Override
3. protectedvoid onCreate(Bundle savedInstanceState){
4. super.onCreate(savedInstanceState);
5. setContentView(R.layout.second);
6. Button btn = (Button) this.findViewById(R.id.button2);
7. final TextView txtview = (TextView) this.findViewById(R.id.second);
8. final Data app = (Data)getApplication();
9. txtview.setText(app.getB());
10. btn.setOnClickListener(new View.OnClickListener() {
11. @Override
12. publicvoid onClick(View v) {
13. // TODO Auto-generated method stub
14. app.setB("hello");
15. txtview.setText(app.getB());
16. Intent intent = new Intent(secondActivity.this, MainActivity.class);
17. startActivity(intent);
18. }
19. });
20. }
21. }

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

1. publicclass Data{
2. privatestatic String a ="feiyangxiaomi";
3. publicstatic String getA() {
4. return a;
5. }
6. publicstaticvoid setA(String a) {
7. Data.a = a;
8. }
9. }

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

1. publicclass MainActivity extends Activity {
2. @Override
3. protectedvoid onCreate(Bundle savedInstanceState) {
4. super.onCreate(savedInstanceState);
5. setContentView(R.layout.main);
6. Button btn = (Button) this.findViewById(R.id.button1);
7. final TextView txtview = (TextView) this.findViewById(R.id.main);
8. txtview.setText(Data.getA());
9. btn.setOnClickListener(new View.OnClickListener() {
10. @Override
11. publicvoid onClick(View v) {
12. // TODO Auto-generated method stub
13. Data.setA("no_feiyangxiaomi");
14. Intent intent = new Intent(MainActivity.this, secondActivity.class);
15. startActivity(intent);
16. }
17. });
18. }
19. }

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

1. publicclass secondActivity extends Activity{
2. @Override
3. protectedvoid onCreate(Bundle savedInstanceState){
4. super.onCreate(savedInstanceState);
5. setContentView(R.layout.second);
6. Button btn = (Button) this.findViewById(R.id.button2);
7. final TextView txtview = (TextView) this.findViewById(R.id.second);
8. txtview.setText(Data.getA());
9. btn.setOnClickListener(new View.OnClickListener() {
10. @Override
11. publicvoid onClick(View v) {
12. // TODO Auto-generated method stub
13. Data.setA("feiyangxiaomi");
14. Intent intent = new Intent(secondActivity.this, MainActivity.class);
15. startActivity(intent);
16. }
17. });
18. }
19. }

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。