What is different between MainActivity.this vs getApplicationContext()
I am trying ProgressDialog.But I am confuse.
1. pd=ProgressDialog.show(MainActivity.this, "", "Fething data");
when I do use (MainActivity.this) then it is ok. But
2. pd=ProgressDialog.show(getApplicationContext(), "", "Fething data");
When I do use (getApplicationContext()) it is ERROR.
What is problem for this progressDialog?
What is different between ( MainActivity.this ) vs ( getApplicationContext() )
and when I use it perfect time?
For getApplicationContext() Error is:
04-09 15:05:37.453: E/AndroidRuntime(9980): FATAL EXCEPTION: main
04-09 15:05:37.453: E/AndroidRuntime(9980): android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.view.ViewRootImpl.setView(ViewRootImpl.java:571)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:246)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.app.Dialog.show(Dialog.java:281)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.app.ProgressDialog.show(ProgressDialog.java:116)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.app.ProgressDialog.show(ProgressDialog.java:99)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.app.ProgressDialog.show(ProgressDialog.java:94)
04-09 15:05:37.453: E/AndroidRuntime(9980): at com.example.shikkok_services.MainActivity$2.onClick(MainActivity.java:27)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.view.View.performClick(View.java:4204)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.view.View$PerformClick.run(View.java:17355)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.os.Handler.handleCallback(Handler.java:725)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.os.Handler.dispatchMessage(Handler.java:92)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.os.Looper.loop(Looper.java:137)
04-09 15:05:37.453: E/AndroidRuntime(9980): at android.app.ActivityThread.main(ActivityThread.java:5041)
04-09 15:05:37.453: E/AndroidRuntime(9980): at java.lang.reflect.Method.invokeNative(Native Method)
04-09 15:05:37.453: E/AndroidRuntime(9980): at java.lang.reflect.Method.invoke(Method.java:511)
04-09 15:05:37.453: E/AndroidRuntime(9980): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-09 15:05:37.453: E/AndroidRuntime(9980): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-09 15:05:37.453: E/AndroidRuntime(9980): at dalvik.system.NativeStart.main(Native Method)
Which context to use?
There are two types of Context:
Application context is associated with the application and will always be same throughout the life of application -- it does not change. So if you are using Toast, you can use application context or even activity context (both) because toast can be displayed from anywhere with in your application and is not attached to a specific window. But there are many exceptions, one exception is when you need to use or pass the activity context.
Activity context is associated with to the activity and can be destroyed if the activity is destroyed -- there may be multiple activities (more than likely) with a single application. And sometimes you absolutely need the activity context handle. For example, should you launch a new activity, you need to use activity context in its Intent so that the new launching activity is connected to the current activity in terms of activity stack. However, you may use application's context too to launch a new activity but then you need to set flag Intent.FLAG_ACTIVITY_NEW_TASK in intent to treat it as a new task.
Let's consider some cases:
MainActivity.this refers to the MainActivity context which extends Activity class but the base class (activity) also extends Context class, so it can be used to offer activity context.
getBaseContext() offers activity context.
getApplication() offers application context.
getApplicationContext() also offers application context.
For more information please check this link.
This explanation is probably missing some subtle nuances but it should give you a better understanding of why one works but the other doesn't.
The difference is that MainActivity.this refers to the the current activity (context) where as the getApplicationContext() refers to the Application class.
The important differences between the 2 is that the Application class never has any UI associations and as such has no window token.
Long story short: For UI items that need context use the Activity.
MainActivity.this refers to the the current activity (context) where the getApplicationContext() refers to the Application class.
The getApplicationContext() method return the context of the single, global Application object of the current process. This generally should only be used if you need a Context whose lifecycle is separate from the current context, that is tied to the lifetime of the process rather than the current component.
MainActivity.this will change when activity destroyed and re-created, getApplicationContext() will change when the application killed and re-started.
链接地址: http://www.djcxy.com/p/24244.html上一篇: 如何以编程方式创建FAB？