Android：ListView的问题（使用意图从另一个活动中将值更新/传递给它）

Question

I have an activity and upon a certain condition, it will pass an integer value to the activity that contains the ListView. However, I am running into several problems:

1. There is an initial value of 0 and when the activity is performed and the condition is met another 0 gets passed in, instead of the actual value.

2. The ListView is reset every time it is run from the main activity. I would like it to keep the results from previous runs (until a user hits a reset button on the ListView activity itself).

**EDIT 3. I have noticed behavior that I did not notice before and that is that every time the ListView activity is opened from the main activity, another 0 is added to the ListView.

Here is the relevant code -

Activity Passing Value to Activity Containing ListView:

if(condition) {
    textview.setText("String1");
    Intent intent = new Intent(this, ListViewActivity.class);
    intent.putExtra("numCounter", numCounter);
}

Activity with ListView:

ListView numListView;
ArrayAdapter<Integer> listAdapter; 

static ArrayList<Integer> numArrayList = new ArrayList<Integer>();

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_name);

    Intent intent = getIntent();
    int intentNum = intent.getIntExtra("numCounter", 0);
    addNumArrayList(intentNum);

    numListView = (ListView) findViewById(R.id.numberListView);

    listAdapter = new ArrayAdapter<Integer>(this, R.layout.listview_row, numArrayList);

    numListView.setAdapter(listAdapter); 
}

// Keep ArrayList to size of 10, while keeping it sorted 
// (displaying only the 10 lowest)

public static void addNumArrayList(int val) {
    numArrayList.add(val);
    Collections.sort(numArrayList);
    if(numArrayList.size() > 10) {
        for(int i = 10; i < numArrayList.size(); i++) {
            numArrayList.remove(i);
        }
    }
}

I basically would like it so that only the other activity or activities can alter it, except when the reset button is hit on the ListView activity itself (simply opening the activity from the main activity should do nothing).

How do I fix it?

Answer 1

Add below condition for addnumArrayList

Bundle mBundle = intent.getExtras();
if(mBundle != null && mBundle.containsKey(¨numCounter¨)){
    int intentNum = intent.getIntExtra("numCounter", 0);
    addNumArrayList(intentNum);
}

You are getting the default value of 0 even if the key is not present. So do check if the key is present

As far as the listView getting reset, you should store values in a file rather than in a static variable, the values will be reset if the process is killed.

Edit: Try this

   int intentNum = intent.getIntExtra("numCounter", -1); // -1 or any number that you do not pass
   if(intentNum != -1)
    addNumArrayList(intentNum);