How Do I Resolve Nullpointerexception When Calling Methods?

I'm a noob to android and i am having an issue calling a method from another class. The method works works fine when called from within its own class, but i get a nullpointerexcep

Solution 1:

If your 2 classes are 2 separated Activities, your case will cause Null Pointer Exception, because when 2nd activity is running, 1st activity is stopped (terminated) -> this is Android OS mechanism, you can not change.

Solutions for your case:

• (1) Activity 1 is parent of others, this case is suitable for Application class or TabHost (complicated).

• (2) Create static method like @Zapl's answer; But it's still not quite nice because this static method should be in common use instead of inside Class 1 -> modify: Create a common Class like following:

This is utility class:

publicclassGlobalUtil
{
    publicstaticvoidstartUrlActivity(Context context, String url) {
    try {
        Intent callIntent = newIntent(Intent.ACTION_CALL);
        callIntent.setData(Uri.parse(url));
        context.startActivity(callIntent); //<-- pass current activity or context
        } catch (ActivityNotFoundException activityException) {
        Log.e("dialing-example", "Call failed", activityException);
        }
    }
}

And inside any other activity class you can call it:

GlobalUtil.startUrlActivity(this, "tel:1234567890"/*+phonenumber0*/");

OR

GlobalUtil.startUrlActivity(getBaseContext().getApplicationContext(), "your_url");

Solution 2:

This will work if call0() is a method of the same activity class.

publicvoidcall0() {
    try {
        Intent callIntent = new Intent(Intent.ACTION_CALL,Uri.parse("tel:1234567890"));
        startActivity(callIntent); 
    } catch (ActivityNotFoundException activityException) {
        Log.e("dialing-example", "Call failed", activityException);
    }
}

And dont forget to add this in your manifest file:

<uses-permissionandroid:name="android.permission.CALL_PHONE"></uses-permission>

And I dont think this a good thing:

BottlesActivityinst=newBottlesActivity();
inst.call0();

Instead when the button is clicked, call call0() like below:

publicvoidonClick(View v) {
     switch(v.getId()){
          case R.id.idButton:
                call0();
                break;

      }
}

Solution 3:

You can't create an Activity yourself. You could use a static method in another Activity class.

from any Activity:

BottlesActivity.call0(this);

in BottlesActivity

publicstaticvoidcall0(Context context) {
    try {
        IntentcallIntent=newIntent(Intent.ACTION_CALL);
        callIntent.setData(Uri.parse("tel:1234567890"/*+phonenumber0*/));
        context.startActivity(callIntent); //<--This line causes nullpointerexception
    } catch (ActivityNotFoundException activityException) {
        Log.e("dialing-example", "Call failed", activityException);
    }
}