Android cannot find method from button's onCli

问题:

I have a ListView populated from a custom adapter. Each row has 1 button in it. In the xml the button has the onClick attribute passed. I have only the xml, not any OnClickListeners set. Also note that the public void myMethod (View v) exists in my CustomActivity. I get the following exception

10-02 03:01:46.463: E/AndroidRuntime(26857): java.lang.IllegalStateException: Could not find a method myClickHandler(View) in the activity class **android.app.Application** for onClick handler on view class android.widget.Button with id 'myButton'

Method in Activity:

public void myClickHandler(View v) {
    ... do stuff here...
}

Button XML:

        <Button 
            android:id="@+id/myButton"
            android:layout_width="44dp"
            android:layout_height="44dp"
            android:background="@drawable/eye_icon"
            android:onClick="myClickHandler"
            />

One Interesting note in the Exception is that the app tries to find the method in android.app.Application and not in my custom Activity.

Any suggestions?

回答1:

It’s important that MyActivity and getContext() of CustomAdapter must be the same instance. Compare yours with mine.

My codes:

MyActivity.java

public class MyActivity extends Activity {
    public static final String TAG = "MyActivity";
    private ListView mListView;
    private CustomAdapter mAdapter;
    private ArrayList<String> mData;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);

        mListView = (ListView) findViewById(R.id.listView);

        mData = new ArrayList<String>();
        mData.add("111");
        mData.add("222");
        mData.add("333");
        mData.add("444");
        mData.add("555");

        mAdapter = new CustomAdapter(this, R.layout.list_item_view, mData);
        mListView.setAdapter(mAdapter);
    }

    public void onClickHandler(View view) {
        Log.i(TAG, "onClickHandler()");
    }
}

CustomAdapter.java

public class CustomAdapter extends ArrayAdapter<String> {

    public CustomAdapter(Context context, int resource, ArrayList<String> objects) {
        super(context, resource, objects);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.list_item_view, null);
        }

        return convertView;
    }
}

activity_my.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MyActivity">

    <ListView
        android:id="@+id/listView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />

</RelativeLayout>

list_item_view.xml

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

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="match_parent"
              android:layout_height="match_parent">
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button"
        android:id="@+id/button"
        android:onClick="onClickHandler"/>
</LinearLayout>

回答2:

When creating the custom Adapter, I was passing as the Context the result of the getApplicationContext() method. This was wrong. I should pass this (my custom Activity) as the Context. It works like a charm now.

回答3:

I'm assuming you wrote a custom adapter for this view so in your adapter when you call getView simply findElementById on the button and set the onClickListener there.

回答4:

This is one example of why the onClick attribute is considered broken. It is probably best to create a custom Adapter and in the getView() method, set the OnClickListener manually.