How do I tell if Intent extras exist in Android?

问题:

I have this code that checks for a value of an extra in an Intent on an Activity that is called from many places in my app:

getIntent().getExtras().getBoolean("isNewItem")

If isNewItem isn't set, will my code crash? Is there any way to tell if it's been set or not before I call it?

What is the proper way to handle this?

回答1:

As others have said, both getIntent() and getExtras() may return null. Because of this, you don't want to chain the calls together, otherwise you might end up calling null.getBoolean("isNewItem"); which will throw a NullPointerException and cause your application to crash.

Here's how I would accomplish this. I think it's formatted in the nicest way and is very easily understood by someone else who might be reading your code.

// You can be pretty confident that the intent will not be null here.
Intent intent = getIntent();

// Get the extras (if there are any)
Bundle extras = intent.getExtras();
if (extras != null) {
    if (extras.containsKey("isNewItem")) {
        boolean isNew = extras.getBoolean("isNewItem", false);

        // TODO: Do something with the value of isNew.
    }
}

You don't actually need the call to containsKey("isNewItem") as getBoolean("isNewItem", false) will return false if the extra does not exist. You could condense the above to something like this:

Bundle extras = getIntent().getExtras();
if (extras != null) {
    boolean isNew = extras.getBoolean("isNewItem", false);
    if (isNew) {
        // Do something
    } else {
        // Do something else
    }
}

You can also use the Intent methods to access your extras directly. This is probably the cleanest way to do so:

boolean isNew = getIntent().getBooleanExtra("isNewItem", false);

Really any of the methods here are acceptable. Pick one that makes sense to you and do it that way.

回答2:

The problem is not the getBoolean() but the getIntent().getExtras()

Test this way:

if(getIntent() != null && getIntent().getExtras() != null)
  myBoolean = getIntent().getExtras().getBoolean("isNewItem");

by the way, if isNewItem doesn't exist, it returns de default vaule false.

Regards.

回答3:

You can do this:

Intent intent = getIntent();
if(intent.hasExtra("isNewItem")) {
   intent.getExtras().getBoolean("isNewItem");
}

回答4:

getIntent() will return null if there is no Intent so use...

boolean isNewItem = false;
Intent i = getIntent();
if (i != null)
    isNewItem = i.getBooleanExtra("isNewItem", false);

回答5:

It will not crash unless until you use it! You don't have to get it if it exists but if you try, for some reason, to use a an "extra" which doesn' exists your system will crash.

So, try o do something like:

final Bundle bundle = getIntent().getExtras();

boolean myBool=false;

if(bundle != null) {
    myBool = bundle.getBoolean("isNewItem");
}

This way you make sure your app won't crash. (and make sure you have a valid Intent :))