java - 无法从适配器调用 Activity 函数

Question

我想从适配器调用 Activity 函数。我正在尝试这样的事情:

 ((MainActivity)mCtx).SampleVoid(); 

但我收到错误:java.lang.ClassCastException:android.app.Application 无法转换为

public void SampleVoid(){

    Toast.makeText(this,"Testowa metoda",Toast.LENGTH_LONG).show();
}

Answer 1

发生该错误是因为您尝试将应用程序上下文转换为 Activity 上下文。首先，我不建议您在适配器内发送和存储上下文。我建议您创建一个接口(interface)，以便在适配器执行特定操作时与 Activity 进行通信。例如:

Activity 代码:

SomeAdapter adapter = new SomeAdapter();
    adapter.setOnAdapterActionListener(new OnAdapterActionListener() {
        @Override
        public void onSomeAdapterAction() {
            Toast.makeText(this,"Testowa metoda",Toast.LENGTH_LONG).show();
        }
    });

适配器代码:

public class SomeAdapter extends ArrayAdapter<String> { // extend from the same adapter that you are extending now.
    private OnAdapterActionListener onAdapterActionListener;

    public SomeAdapter(@NonNull Context context, int resource, @NonNull List<String> objects) {
        super(context, resource, objects);
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        View view = super.getView(position, convertView, parent);
        view.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(onAdapterActionListener != null) {
                    onAdapterActionListener.onSomeAdapterAction();
                }
            }
        });
        return view;
    }

    public void setOnAdapterActionListener(OnAdapterActionListener onAdapterActionListener) {
        this.onAdapterActionListener = onAdapterActionListener;
    }
}

interface OnAdapterActionListener {
    void onSomeAdapterAction();
}