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。