Java接口回调机制解析与应用-优快云博客

本文链接：https://blog.youkuaiyun.com/wangzunkuan/article/details/79232224

Java接口回调在adapter和事件监听中发挥关键作用。通过定义接口，由Activity实现并处理点击事件，adapter则利用接口对象进行交互。回调机制包括定义接口、注册回调引用和在特定条件下调用接口方法来响应事件。

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java中的接口回调比较简单，但是很重要，也很实用。它经常运用于各种adapter中，可以监听adapter中的点击事件，也运用于很多其他的需要监听某些事件的场合。
稍微举一个小例子，展示一下接口回调在adapter中的应用。
1）先定义一个接口

public interface OnItemClickListener {
    void onItemClick(int position,View view);
}

2）activity实现这个接口，并覆写其中的方法（用于处理点击事件）

public class CallbackActivity extends Activity implements OnItemClickListener {
    private ListView mListView;
    private CallbackAdapter mCallbackAdapter;
    private ArrayList<String> mArrayList = new ArrayList<>();

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_call_back);
        mArrayList.add("harry");
        mArrayList.add("mike");
        mArrayList.add("lucy");
        mListView = (ListView) findViewById(R.id.lsv);
        mCallbackAdapter = new CallbackAdapter(CallbackActivity.this, mArrayList, CallbackActivity.this);
        mListView.setAdapter(mCallbackAdapter);
    }

    @Override
    public void onItemClick(int position, View view) {
        Toast.makeText(CallbackActivity.this, "点击了第 " + position + " 项", Toast.LENGTH_SHORT).show();
    }
}

写得随意了点，领会要旨即可。
3）adapter中使用接口对象

public class CallbackAdapter extends BaseAdapter {
    private Context mContext;
    private ArrayList<String> mList;
    private LayoutInflater mLayoutInflater;
    private OnItemClickListener mOnItemClickListener;

    public CallbackAdapter(Context context, ArrayList<String> list, OnItemClickListener onItemClickListener) {
        this.mContext = context;
        this.mList = list;
        this.mOnItemClickListener = onItemClickListener;
        this.mLayoutInflater = LayoutInflater.from(context);
    }

    public final class ViewHolder {
        TextView mTittle;
    }

    @Override
    public int getCount() {
        return mList.size();
    }

    @Override
    public Object getItem(int i) {
        return mList.get(i);
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public View getView(final int position, View convertView, ViewGroup viewGroup) {
        final ViewHolder viewHolder;
        if (convertView == null) {
            viewHolder = new ViewHolder();
            convertView = mLayoutInflater.inflate(R.layout.item_callback, null);
            viewHolder.mTittle = (TextView) convertView.findViewById(R.id.tv_tittle);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        viewHolder.mTittle.setText(mList.get(position));
        viewHolder.mTittle.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mOnItemClickListener.onItemClick(position,view);
            }
        });
        return convertView;
    }
}