Android中用Application类实现全局变量
在Java中如果要使用全局变量，一般定义public static类型的变量。但是这种方法不符合Android的框架架构，Android中要使用Application context。
Application是一个基类，这个基类的作用是获取整个App的状态，我们需要自己定义一个类来继承这个基类。代码如下：
[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();
}
}
我们定义了一个MyApplication继承自Application，并定义了一个全局变量mHasPassword，然后复写基类的onCreate方法，onCreate负责对所有全局变量赋初期值。
我们还需要把自定义的Application类添加到AndroidManifest.xml里面，代码如下：
[html] view plaincopyprint?<application
android:name="MyApplication"
。。。。。。。。。。。。。。。。。。。。。。。。。。。
。。。。。。。。。。。。。。。。。。。。。。。。。。。
</application>
<application
android:name="MyApplication"
。。。。。。。。。。。。。。。。。。。。。。。。。。。
。。。。。。。。。。。。。。。。。。。。。。。。。。。
</application>
这样做的目的：App的进程被创建的时候，这个类就会被实例化，onCreate方法就会被执行，给所有全局变量赋初期值。
这样，所有的Activity就共同拥有这个类里面的变量了。
下面用两个Activity来测试一下，当一个Activity改变了全局变量的值之后，看看另一个Activity能不能取到改变后的值。
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(savedInsta
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