android 公共變量使用

在我們使用Android編寫程序的時候，少不了想利用全局變量，但是面嚮對象語言和過程語言區別很大，不再是include就可以的。這裏我寫了使用全局變量的兩種方法：

 

1.使用application來保存全局變量                                                             

這裏沒有太多理論性的東西，無非就是一些實際操作。

1.1定義Data類繼承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中聲明application

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

1.3創建兩個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運行程序
    

說明：程序首先進入MainActivity.class中，獲取Data中變量b的值，顯示圖1所示的界面hello，單擊button後app.setB("no_hello")， 修改變量b的值。

           跳轉到secondActivity.class，獲取Data中變量b的值，顯示圖2所示的界面no_hello，單擊button後app.setB("hello")， 修改變量b的值。

           跳轉回MainActivity.class……  循環

2.使用普通的類Data.class來保存全局變量                                                             

方法和上面差不多。

1.1 定義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創建兩個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運行程序
                      

說明：程序首先進入MainActivity.class中，獲取Data中變量b的值，顯示圖1所示的界面feiyangxiaomi，單擊button後app.setB("no_feiyangxiaomi")， 修改變量b的值。

           跳轉到secondActivity.class，獲取Data中變量b的值，顯示圖2所示的界面no_feiyangxiaomi，單擊button後app.setB("feiyangxiaomi")， 修改變量b的值。

           跳轉回MainActivity.class……  循環

3.總結                                                                                        

    兩種方法我測試的都可以的，大多數人應該更會偏向於第一種，畢竟Application是android專門提供的應用入口，並且運行週期貫穿整個程序運行。