Question

我正在关注本教程http://javatechig.com/android/android-recyclerview-example

完成编码后，我得到一个错误android.view.View无法转换为android.support.v7.widget.RecyclerView。提前谢谢

我的MainActivity.java

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "RecyclerViewExample";
    private List<FeedItem> feedsList;
    private RecyclerView mRecyclerView;
    private MyRecyclerAdapter adapter;
    private ProgressBar progressBar;

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

        // Initialize recycler view
        mRecyclerView = (RecyclerView) findViewById(R.id.recyclerd_view);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));

        progressBar = (ProgressBar) findViewById(R.id.progress_bar);
        progressBar.setVisibility(View.VISIBLE);

        // Downloading data from below url
        final String url = "http://javatechig.com/?json=get_recent_posts&count=45";
        new AsyncHttpTask().execute(url);
    }

    public class AsyncHttpTask extends AsyncTask<String, Void, Integer> {

        @Override
        protected void onPreExecute() {
            setProgressBarIndeterminateVisibility(true);
        }

        @Override
        protected Integer doInBackground(String... params) {
            Integer result = 0;
            HttpURLConnection urlConnection;
            try {
                URL url = new URL(params[0]);
                urlConnection = (HttpURLConnection) url.openConnection();
                int statusCode = urlConnection.getResponseCode();

                // 200 represents HTTP OK
                if (statusCode == 200) {
                    BufferedReader r = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = r.readLine()) != null) {
                        response.append(line);
                    }
                    parseResult(response.toString());
                    result = 1; // Successful
                } else {
                    result = 0; //"Failed to fetch data!";
                }
            } catch (Exception e) {
                Log.d(TAG, e.getLocalizedMessage());
            }
            return result; //"Failed to fetch data!";
        }

        @Override
        protected void onPostExecute(Integer result) {
            // Download complete. Let us update UI
            progressBar.setVisibility(View.GONE);

            if (result == 1) {
                adapter = new MyRecyclerAdapter(MainActivity.this, feedsList);
                mRecyclerView.setAdapter(adapter);
            } else {
                Toast.makeText(MainActivity.this, "Failed to fetch data!", Toast.LENGTH_SHORT).show();
            }
        }
    }

    private void parseResult(String result) {
        try {
            JSONObject response = new JSONObject(result);
            JSONArray posts = response.optJSONArray("posts");
            feedsList = new ArrayList<>();

            for (int i = 0; i < posts.length(); i++) {
                JSONObject post = posts.optJSONObject(i);
                FeedItem item = new FeedItem();
                item.setTitle(post.optString("title"));
                item.setThumbnail(post.optString("thumbnail"));

                feedsList.add(item);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
}

activity_main.xml中

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:class="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:id="@+id/relativ"
    tools:context="com.example.ict4.recyclerviewasyntask.MainActivity">

 <View
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:id="@+id/recyclerd_view"
     android:layout_centerInParent="true"
     class="android.support.v7.widget.RecyclerView"/>
    <ProgressBar
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/progress_bar"
        android:layout_centerInParent="true"
        />
</RelativeLayout>

Answer 1

在 XML 布局中，更改

<View
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:id="@+id/recyclerd_view"
 android:layout_centerInParent="true"
 class="android.support.v7.widget.RecyclerView"/>

到

<android.support.v7.widget.RecyclerView
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:id="@+id/recyclerd_view"
 android:layout_centerInParent="true" />

android.view.View无法强制转换为android.support.v7.widget.RecyclerView

1 个答案: