Summary of the use of global variables and local variables in Android

As the name implies, global variables are variables that can be called in the entire class or in multiple functions. They are also called external variables. Local variables are variables that can be accessed in a specific procedure or function. It is easy to declare a variable, but when it comes to using it, it is not as simple as imagined. As for me, I often define global variables for use, but because of this, I define global variables. It also takes a lot of detours.

When using Adapter, it is usually used with listView, because a listView basically has a layout of listView items. The following scenario is: there is an ImageView in each item. When I click on an item, I need to change the background color of the ImageView of the item or change it to another background image. At this time, a situation may occur that you clearly click on the first item, but you will find that the image of the third or second item has also changed. This is because you define a global variable. The code part is as follows:

 public class Adapter extends BaseAdapter {
 private ImageView img; 
 
 public   View getView( int position, View convertView, ViewGroup parent) {
 convertView = mInflater.inflate(R.layout.group_listview_item, null );
 img = (ImageView) convertView.findViewById(R.id.logo); 
 
 return convertView; 
 
 } }

In the above part, ImageView is a global variable. At this time, we need to define ImageView as a local variable.

 public class Adapter extends BaseAdapter { 
 
 public   View getView( int position, View convertView, ViewGroup parent) {
     convertView = mInflater.inflate(R.layout.group_listview_item, null );
     ImageView img = (ImageView) convertView.findViewById(R.id.logo); 
 
 return convertView; 
 
 } }

This means that each Item has an ImageView. Another case is when you are making a shopping cart, you can click the plus and minus icons to change the number of items in the shopping cart. When you define the number num, you must also define it as a local variable. It would be better if you can use ViewHolder.