Android Popup Window vs Android Dialog

问题:

I am trying to implement a simple logic in my application where the user is shown a popup (after sometime of application launch). The popup simply shows a TextView with some info message. This message is refreshed every time the application is launched and a new message is shown. The UI of the popup matches my application UI - here maybe just popup background images is needed. Also one close button (X) is shown at the top right corner of the popup - to close this popup.

Logic of Showing Message: I have a String array having some 100 strings stored in it. I randomly pick one string from this array and populate the popup TextView showing the message. Please suggest if there is any better approach than what I am doing already here. Also is it possible to logic that if one message is picked then the same message is not picked until the other messages are shown at least once?

Logic of Showing Popup: This is what I am not able to implement. I do not want to anchor the popup with any user Event or Button click. I simply wants to show the message after some time - say

Thread.sleep(3000);

Now I have tried to use PopupWindow for this using the below code.

PopupWindow infoPopup;    
LinearLayout infoLayout;
TextView infoTextView;
Button infoButton;
infoTextView = new TextView(this);
infoTextView.setText("Testing Popup Text");
infoTextView.setPadding(10,10,10,10);
infoButton = new Button(this);
infoButton.setText("Close");    
infoLayout = new LinearLayout(this);
infoLayout.setOrientation(LinearLayout.VERTICAL);
infoLayout.addView(infoTextView);
infoLayout.addView(infoButton);    
infoPopup = new PopupWindow(infoLayout,LinearLayout.LayoutParams.MATCH_PARENT,LinearLayout.LayoutParams.WRAP_CONTENT);
infoPopup.setContentView(infoLayout);    
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}    
infoPopup.showAtLocation((CoordinatorLayout)findViewById(R.id.main_content),Gravity.CENTER,100,100);

But this popup is showing error at the last line giving null pointer on my

(CoordinatorLayout)findViewById(R.id.main_content)

parameter.

The issue that I am getting are:

1. First of all, I am not sure if this is the right approach of showing a custom UI popup. I am aware of AlertDialog but not sure which is the best option to go in this case - Please suggest.

2. Why the CoordinatorLayout is showing null pointer?

3. How to implement the top right (X) button logic in this Popup ?

回答1:

1. Yes there are so many options for showing a custom UI popup in Android. You might select one from PopupWindow, AlertDialog or Dialog Activity. You need to decide which suits you best.

If you need to customize your UI a lot and have to show a list or some complex GUI then I would suggest you launch an Activity with theme.Dialog. Just set the theme of the Activity to something like this android:theme="@android:style/Theme.Holo.Light.Dialog". There's a plenty of tutorials for implementing a dialog Activity.

PopupWindow is another tool to customize your custom pop up anywhere in the screen. If you're showing this popup always in the middle of the screen, then I would like to suggest not to use this. The AlertDialog should work fine.

AlertDialog has many variants and as far as I can assume your problem, this one suits you best. You can have a cross button too in the top-right corner of the dialog (You can set the icons anywhere, as you can provide a custom layout to an AlertDialog). Personally I use this library to provide a custom layout to my AlertDialog. You can have a look at this too.

2. The NullPointerException is simple. Your layout doesn't have any id named main_content. Post your logcat if this doesn't solve your problem. Post the layout too.

3. As I've told you earlier, I use the library to provide a custom layout to an AlertDialog and you can have a look at it too. So after implementing this library you can easily design your own layout with a cross button and implement the onClick functionalities easily.

Hope this helps.

回答2:

1. Activity with theme Dialog.
   This is not a good idea. It looks like a pop-up, but you can't click outside the pop-up to close it.

2. PopupWindow
   It will stop the application. When the user finish clicking the pop-up, the application can work again.

3. AlertDialog
   The best one, it will not stop the application and can be closed by clicking outside the dialog.