为什么我们使用界面在主活动中设置回收器视图的视图持有人

Question

我正在学习一个教程，该教程使用回收器视图显示一周内每天的天气列表。 我困惑于两类：

预测适配器和主活动

下面是上述两个类的代码：

预测适配器.java

public class ForecastAdapter extends RecyclerView.Adapter<ForecastAdapter.ForecastAdapterViewHolder> {
private String[] mWeatherData;
final private ForecastAdapterOnClickListener mClickHandler;
//Why do we need to create an interface here.
public interface ForecastAdapterOnClickListener {
void onClick(String weatherForDay);
}
public ForecastAdapter(ForecastAdapterOnClickListener forecastAdapterOnClickListener) {
mClickHandler = forecastAdapterOnClickListener;
}

public class ForecastAdapterViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{
public final TextView mWeatherTextView;
public ForecastAdapterViewHolder(View view) {
super(view);
mWeatherTextView = (TextView) view.findViewById(R.id.tv_weather_data);
view.setOnClickListener(this);
}
@Override
public void onClick(View v) {
int adapterPosition = getAdapterPosition();
String weatherForDay = mWeatherData[adapterPosition];
//Why are we calling onClick from mClickHandler here. Why can't we just display Toast here. 
mClickHandler.onClick(weatherForDay); 
/*Why can't we just display the Toast from here like this:
Toast.makeText(v.getContext(), weatherForDay, Toast.LENGTH_SHORT).show()
*/
}
}

@Override
public ForecastAdapterViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
Context context = viewGroup.getContext();
int layoutIdForListItem = R.layout.forecast_list_item;
LayoutInflater inflater = LayoutInflater.from(context);
boolean shouldAttachToParentImmediately = false;
View view = inflater.inflate(layoutIdForListItem, viewGroup, shouldAttachToParentImmediately);
return new ForecastAdapterViewHolder(view);
}

@Override
public void onBindViewHolder(ForecastAdapterViewHolder forecastAdapterViewHolder, int position) {
String weatherForThisDay = mWeatherData[position];
forecastAdapterViewHolder.mWeatherTextView.setText(weatherForThisDay);
}

@Override
public int getItemCount() {
if (null == mWeatherData) return 0;
return mWeatherData.length;
}

public void setWeatherData(String[] weatherData) {
mWeatherData = weatherData;
notifyDataSetChanged();
}
}

主要活动.java

//Why are implementing ForecastAdapterOnClickListener here?
public class MainActivity extends AppCompatActivity implements ForecastAdapter.ForecastAdapterOnClickListener{
private RecyclerView mRecyclerView;
private ForecastAdapter mForecastAdapter;
private TextView mErrorMessageDisplay;
private ProgressBar mLoadingIndicator;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_forecast);
mRecyclerView = (RecyclerView) findViewById(R.id.recyclerview_forecast);
mErrorMessageDisplay = (TextView) findViewById(R.id.tv_error_message_display);
LinearLayoutManager layoutManager
= new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
mRecyclerView.setLayoutManager(layoutManager);

mRecyclerView.setHasFixedSize(true);

mForecastAdapter = new ForecastAdapter(this);
mRecyclerView.setAdapter(mForecastAdapter);

mLoadingIndicator = (ProgressBar) findViewById(R.id.pb_loading_indicator);
loadWeatherData();
}

private void loadWeatherData() {
showWeatherDataView();
String location = SunshinePreferences.getPreferredWeatherLocation(this);
new FetchWeatherTask().execute(location);
}

@Override
public void onClick(String weatherForDay) {
Context context = this;
Toast.makeText(context, weatherForDay, Toast.LENGTH_SHORT)
.show();
}

private void showWeatherDataView() {
mErrorMessageDisplay.setVisibility(View.INVISIBLE);
mRecyclerView.setVisibility(View.VISIBLE);
}

private void showErrorMessage() {
mRecyclerView.setVisibility(View.INVISIBLE);
mErrorMessageDisplay.setVisibility(View.VISIBLE);
}
public class FetchWeatherTask extends AsyncTask<String, Void, String[]> {
@Override
protected void onPreExecute() {
super.onPreExecute();
mLoadingIndicator.setVisibility(View.VISIBLE);
}
@Override
protected String[] doInBackground(String... params) {
if (params.length == 0) {
return null;
}
String location = params[0];
URL weatherRequestUrl = NetworkUtils.buildUrl(location);
try {
String jsonWeatherResponse = NetworkUtils
.getResponseFromHttpUrl(weatherRequestUrl);
String[] simpleJsonWeatherData = OpenWeatherJsonUtils
.getSimpleWeatherStringsFromJson(MainActivity.this, jsonWeatherResponse);
return simpleJsonWeatherData;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
@Override
protected void onPostExecute(String[] weatherData) {
mLoadingIndicator.setVisibility(View.INVISIBLE);
if (weatherData != null) {
showWeatherDataView();
mForecastAdapter.setWeatherData(weatherData);
} else {
showErrorMessage();
}
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.forecast, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_refresh) {
mForecastAdapter.setWeatherData(null);
loadWeatherData();
return true;
}
return super.onOptionsItemSelected(item);
}

}

适配器、视图持有人和回收器视图按预期工作。我们现在应该在回收器视图的行上实现单击处理。每当单击特定行时，我们都应该显示一个 Toast。

如您所见，我们正在 ForecastAdapterViewHolder 中实现 OnClickListener，而在 onClick 函数中，我们调用接口的 onClick "ForecastAdapterOnClickListener"。 在 MainActivity.java 中，我们正在实现这个"ForecastAdapterOnClickListener"，然后显示 toast。

为什么我们不能只在为"ForecastAdapterViewHolder"类定义的onClick中显示Toast。我已经尝试过了，它有效。执行代码中正在执行的操作有什么意义？ 这样设置点击侦听器有什么好处吗？

Answer 1

因为之后您必须显示信息，并且不是 ViewHolder 的角色，也不是适配器。活动/片段必须这样做。 这是为了让你的代码井井有条。