custom grid view, with image and checkbox crashing - android-gridview

Question

in MainActivity.java I am reading a list from a txt file then on a show list button I am able to display the list, with list items, images and checkbox using custom grid view. Now with another button click I am trying to get checked item's position so as I can use these selected items. the code I have is giving me a null pointer exception error on . view.getCheckedItemPositions();
MainActivity.java
if(v.getId()==R.id.toast)
{
Toast.makeText(this,"positions" + adapter.getCheckedItemPositions(view), Toast.LENGTH_SHORT).show();
}
}
public class CustomAdapter extends BaseAdapter {
#Override
public View getView(int position, View view, ViewGroup parent) {
LinearLayout layout = new LinearLayout(getApplicationContext());
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
view = new View(getApplicationContext());
TextView text=new TextView(getApplicationContext());
text.setTextColor(Color.BLACK);
text.setText(content.get(position));
CheckBox checkBox = new CheckBox(getApplicationContext());
checkBox.setChecked(!checkBox.isChecked());
checkBox.setChecked(true);
layout.addView(checkBox);
layout.addView(text);
return layout;
}
public List<Integer> getCheckedItemPositions(GridView view){
SparseBooleanArray checked = new SparseBooleanArray();
checked = view.getCheckedItemPositions();
List<Integer> positions = new ArrayList<>();
int checksize=checked.size();
for(int i=0; i<checksize; i++) {
if (checked.valueAt(i)) {
positions.add(checked.keyAt(i));
}
}
return positions;
}
}
}
Activity_main.xml
<GridView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/gridView"
android:layout_below="#+id/button"
android:layout_alignParentStart="true"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Toast"
android:id="#+id/toast"
android:layout_alignParentTop="true"
android:layout_alignEnd="#+id/gridView"
android:layout_marginEnd="49dp" />
</RelativeLayout>
logcat
--------- beginning of crash
09-18 18:31:49.144 31751-31751/com.example.administrator.myapplication E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.administrator.myapplication, PID: 31751
java.lang.NullPointerException: Attempt to invoke virtual method 'int android.util.SparseBooleanArray.size()' on a null object reference
at com.example.administrator.myapplication.MainActivity$CustomAdapter.getCheckedItemPositions(MainActivity.java:158)
at com.example.administrator.myapplication.MainActivity.onClick(MainActivity.java:96)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
09-18 18:32:26.135 31751-31758/com.example.administrator.myapplication W/art﹕ Suspending all threads took: 102.748ms
09-18 18:32:27.078 31751-31758/com.example.administrator.myapplication W/art﹕ Suspending all threads took: 78.288ms

Answer 1

I got the answer..
I created a link hash map with string as position of the check box and value as the boolean value at that position. Like
LinkedHashMap mylist = new LinkedHashMap<>();
Now in order to get the status of the checked item and monitor it in runntime we have to set a Listener on checkbox either using
checkBox.setOnCheckedChangeListener();
or //
checkbox.setOnClickListener()
either of these two works.
Earlier I was just setting up the checkbox but not setting up a listener on the check box as above
checkBox.setChecked(!checkBox.isChecked());
checkBox.setChecked(true);
Now with setOnClickListener all I have to do is store the position and boolean value of the checkbox to the LinkHashmap.
checkBox.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
if (((CheckBox) v).isChecked()) {
saveValues("check" + position, true);
Toast.makeText(MainActivity.this,"position: "+getValues("check"+position), Toast.LENGTH_SHORT).show();
}
else {
saveValues("check"+position,false);
}
}
});
Later on I can see the checked items using
public Boolean getValues(String a){
return mylist.get(a).booleanValue();
}
I am really thankful to the contributors of the below post
Android: checkbox listener