在Java中如果要使用全局變量,一般定義public static類型的變量。但是這種方法不符合Android的框架架構,Android中要使用Application context。
Application是一個基類,這個基類的作用是獲取整個App的狀態,我們需要自己定義一個類來繼承這個基類。代碼如下:
[java]
package com.tianjf;
import android.app.Application;
public class MyApplication extends Application {
private boolean mHasPassword;
public boolean ismHasPassword() {
return mHasPassword;
}
public void setmHasPassword(boolean mHasPassword) {
this.mHasPassword = mHasPassword;
}
@Override
public void onCreate() {
mHasPassword = true;
super.onCreate();
}
}
package com.tianjf;
import android.app.Application;
public class MyApplication extends Application {
private boolean mHasPassword;
public boolean ismHasPassword() {
return mHasPassword;
}
public void setmHasPassword(boolean mHasPassword) {
this.mHasPassword = mHasPassword;
}
@Override
public void onCreate() {
mHasPassword = true;
super.onCreate();
}
}
我們定義瞭一個MyApplication繼承自Application,並定義瞭一個全局變量mHasPassword,然後復寫基類的onCreate方法,onCreate負責對所有全局變量賦初期值。
我們還需要把自定義的Application類添加到AndroidManifest.xml裡面,代碼如下:
[html] view plaincopyprint?<application
android:name="MyApplication"
。。。。。。。。。。。。。。。。。。。。。。。。。。。
。。。。。。。。。。。。。。。。。。。。。。。。。。。
</application>
<application
android:name="MyApplication"
。。。。。。。。。。。。。。。。。。。。。。。。。。。
。。。。。。。。。。。。。。。。。。。。。。。。。。。
</application>
這樣做的目的:App的進程被創建的時候,這個類就會被實例化,onCreate方法就會被執行,給所有全局變量賦初期值。
這樣,所有的Activity就共同擁有這個類裡面的變量瞭。
下面用兩個Activity來測試一下,當一個Activity改變瞭全局變量的值之後,看看另一個Activity能不能取到改變後的值。
ApplicationDemoActivity.java
[java]
package com.tianjf;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
public class ApplicationDemoActivity extends Activity implements
OnClickListener {
private static final String TAG = "ApplicationDemoActivity";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
findViewById(R.id.button).setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.button:
MyApplication myApplication = (MyApplication) getApplication();
Log.i(TAG, String.valueOf(myApplication.ismHasPassword()));
myApplication.setmHasPassword(false);
Intent intent = new Intent(this, AnotherActivity.class);
startActivity(intent);
break;
default:
break;
}
}
}
package com.tianjf;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
public class ApplicationDemoActivity extends Activity implements
OnClickListener {
private static final String TAG = "ApplicationDemoActivity";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
findViewById(R.id.button).setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.button:
MyApplication myApplication = (MyApplication) getApplication();
Log.i(TAG, String.valueOf(myApplication.ismHasPassword()));
myApplication.setmHasPassword(false);
Intent intent = new Intent(this, AnotherActivity.class);
startActivity(intent);
break;
default:
break;
}
}
}
AnotherActivity.java
[java]
package com.tianjf;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
public class AnotherActivity extends Activity {
private static final String TAG = "AnotherActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.another);
MyApplication myApplication = (MyApplication) getApplication();
Log.i(TAG, String.valueOf(myApplication.ismHasPassword()));
}
}
package com.tianjf;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
public class AnotherActivity extends Activity {
private static final String TAG = "AnotherActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.another);
MyApplication myApplication = (MyApplication) getApplication();
Log.i(TAG, String.valueOf(myApplication.ismHasPassword()));
}
}
main.xml[html]
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
<Button
android:id="@+id/button"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Start another activity" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
<Button
android:id="@+id/button"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Start another activity" />
</LinearLayout>
another.xml[html] view plaincopyprint?<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
</LinearLayout>
運行一下看看結果。
作者:tianjf0514