What the actual meaning `Caused by: java.lang.Runt

Question

Please inform me if knowing whats tag that wanted.

Caused by: java.lang.RuntimeException: view must have a tag

__BaseActivity.java

    @Override
    public void setContentView(int layoutResID) {

        mBinding.contentParent.removeAllViews();
        DataBindingUtil.inflate(LayoutInflater.from(this), layoutResID, mBinding.contentParent, true);
        super.setContentView(mBinding.getRoot());
    }

__ChildActivity.java

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mBinding = DataBindingUtil.setContentView(this, R.layout.my_wallet);
}

ERROR logcat

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mydev}: java.lang.RuntimeException: view must have a tag
        at <more...>
     Caused by: java.lang.RuntimeException: view must have a tag
        at android.databinding.DataBinderMapperImpl.getDataBinder(DataBinderMapperImpl.java:121)

Answer 1

Another scenario where this error occurs is in a RecyclerView's ViewHolder.

Avoid initialising a binding instance in the ViewHolder's bind method

class BindingAdapter(private val items: List<Any>): RecyclerView.Adapter<BindingHolder>() {
      override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): BindingHolder {}

      override fun onBindViewHolder(holder: BindingHolder, position: Int) {
           holder.bindItem(items[position])
      }
 }

class BindingHolder(view: View): RecyclerView.ViewHolder(view) {
    fun bindItem(item: Any) {
        //Don't do this
        val binding = ItemSampleBinding.bind(itemView)
    }
}

The databinding instance should be initialised outside the bind method because ViewHolders could be recycled and in the code above we could be trying to create a binding instance from a view that's already bound.

Instead create the binding instance in initialisation block of the ViewHolder (this can be in init{} block or just after the class declaration as shown below)

class BindingHolder(view: View): RecyclerView.ViewHolder(view) {
    val binding = ItemSampleBinding.bind(view)

    fun bindItem(item: Any) {
        //Rest of ViewHolder logic
        //binding.textView.text = "Something nice"
    }
}

Answer 2

This usually happens when attempting to use DataBindingUtil.inflate() to inflate a layout that does not support data binding. In other words, the layout you're attempting to inflate does not have its root element as <layout>.

I have run into this problem when refactoring an Activity to use data binding, and the Activity has multiple layouts. I successfully refactored one of the layouts to include the <layout> element at its root, but I didn't refactor all the other layouts (layouts for other screen densities, languages, modules, etc.).

Check to make sure ALL the possible matching layouts are configured with <layout> as their root element.

See this developer doc Layouts and binding expressions