为什么我的应用程序由于ImageView而崩溃？

Question

I am trying to get a FloatingButton in a fragment.

XML:

<?xml version="1.0" encoding="utf-8"?>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Demand"
    android:id="@+id/frag_demand"
    android:layout_gravity="center_horizontal|top"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />

<ImageView
    android:layout_width="65dp"
    android:layout_height="65dp"
    android:id="@+id/imageButton"
    android:background="@drawable/oval"
    android:elevation="10dp"
    android:layout_alignParentBottom="true"
    android:layout_alignParentEnd="true"
    android:layout_marginBottom="20dp"
    android:layout_marginRight="15dp"
    android:src="@drawable/ic_menu_add"/>

JAVA:

public class DemandFragment extends Fragment {

    MenuItem fav;

    ImageButton floatButton;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_demand, container, false);

        floatButton = (ImageButton) rootView.findViewById(R.id.imageButton);
        floatButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Snackbar.make(v, "Replace with your own action", Snackbar.LENGTH_LONG);
            }
        });

        return rootView;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setHasOptionsMenu(true);

    }
}

logcat gives:

java.lang.ClassCastException: android.widget.ImageView cannot be cast to android.widget.ImageButton

Why is this not working?

help

Answer 1

From the given exception

java.lang.ClassCastException: android.widget.ImageView cannot be cast to android.widget.ImageButton

It is very clear that you are trying to Cast ImageView into an ImageButton. In your case, in your xml you have defined ImageView with id imageButton

<ImageView
android:layout_width="65dp"
android:layout_height="65dp"
android:id="@+id/imageButton"
android:background="@drawable/oval"
android:elevation="10dp"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:layout_marginBottom="20dp"
android:layout_marginRight="15dp"
android:src="@drawable/ic_menu_add"/>

but in your Fragment code, you are doing this

floatButton = (ImageButton) rootView.findViewById(R.id.imageButton);

where floatButton is an ImageButton not ImageView as you defined in your xml and hence the exception.

Try changing ImageView to ImageButton in your xml or ImageButton to ImageView in your Fragment Code. Doing it any way will work

Answer 2

Why is it crashing? ImageViews do not extend from ImageButtons . And your java code expects this to not be the case.

To fix, You have two options.

1 - Since one can always call setOnClickListener on any view, Change your reference of floatButton to a View.

View floatButton;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_demand, container, false);

    floatButton = rootView.findViewById(R.id.imageButton);
    floatButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Snackbar.make(v, "Replace with your own action", Snackbar.LENGTH_LONG);
        }
    });

    return rootView;
}

2 - Or, should you actually want an ImageButton, change your xml layout to use an ImageButton (instead of ImageView) and don't change any Java code:

<?xml version="1.0" encoding="utf-8"?>
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Demand"
    android:id="@+id/frag_demand"
    android:layout_gravity="center_horizontal|top"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />

<ImageButton
    android:layout_width="65dp"
    android:layout_height="65dp"
    android:id="@+id/imageButton"
    android:background="@drawable/oval"
    android:elevation="10dp"
    android:layout_alignParentBottom="true"
    android:layout_alignParentEnd="true"
    android:layout_marginBottom="20dp"
    android:layout_marginRight="15dp"
    android:src="@drawable/ic_menu_add"/>

Answer 3

floatButton = (ImageButton) rootView.findViewById(R.id.imageButton);

but in your xml it is an ImageView . You have to change that to ImageButton in xml or vice versa.

You can not cast ImageView in your xml to ImageButton.