我正在构建一个带有列表视图的 android 应用程序，当单击一个项目时，它会打开另一个列表视图。我已经通过存储在应用程序资源的 strings.xml 文件中的几个字符串数组完成了这项工作。
但是现在我想通过我创建的 API 获取数据项，并给出 JSON 对象。我不确定如何获取 JSON 对象并将课程名称作为列表视图中的列表项查看。
当单击“化学”（在 MainActivity 中）和“ http://alvideobackend.azurewebsites.net/lesson/Physics时，我想从 SecondActivity 中的“ http://alvideobackend.azurewebsites.net/lesson/Chemistry ”获取课程名称单击“Physics”（在 MainActivity 中）时在 SecondActivity 中
以下是我尝试过的 MainActivity.java 和 SecondActivity.java
主活动.java
package com.example.acer.videoapp;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.support.v7.widget.Toolbar;
public class MainActivity extends AppCompatActivity {
Toolbar toolbar;
ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = (Toolbar) findViewById(R.id.toolbar);
toolbar.setTitle(getResources().getString(R.string.app_name));
listView = (ListView) findViewById(R.id.listView);
ArrayAdapter<String> mAdapter = new ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_expandable_list_item_1,getResources().getStringArray(R.array.subjects));
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int i, long id) {
Intent intent = new Intent(MainActivity.this,SecondActivity.class);
intent.putExtra("Subject",listView.getItemAtPosition(i).toString());
startActivity(intent);
}
});
listView.setAdapter(mAdapter);
}
}
第二个Activity.java
package com.example.acer.videoapp;
import android.content.Intent;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class SecondActivity extends AppCompatActivity {
Toolbar toolbar1;
ListView listView1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
toolbar1 = (Toolbar) findViewById(R.id.toolbar1);
listView1 = (ListView) findViewById(R.id.listView1);
Bundle bundle = getIntent().getExtras();
if(bundle!=null){
toolbar1.setTitle(bundle.getString("Subject"));
if(toolbar1.getTitle().toString().equalsIgnoreCase("Chemistry")){
//new JSONTask().execute("http://alvideobackend.azurewebsites.net/lesson/Chemistry");
ArrayAdapter<String> mAdapter = new ArrayAdapter<String>(SecondActivity.this,android.R.layout.simple_expandable_list_item_1,getResources().getStringArray(R.array.Chemistry));
listView1.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int i, long id) {
Intent intent1 = new Intent(SecondActivity.this, ThirdActivity.class);
intent1.putExtra("Lesson", listView1.getItemAtPosition(i).toString());
startActivity(intent1);
}
});
listView1.setAdapter(mAdapter);
}
else if(toolbar1.getTitle().toString().equalsIgnoreCase("Physics")){
ArrayAdapter<String> mAdapter = new ArrayAdapter<String>(SecondActivity.this,android.R.layout.simple_expandable_list_item_1,getResources().getStringArray(R.array.Physics));
listView1.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int i, long id) {
Intent intent1 = new Intent(SecondActivity.this, ThirdActivity.class);
intent1.putExtra("Lesson", listView1.getItemAtPosition(i).toString());
startActivity(intent1);
}
});
listView1.setAdapter(mAdapter);
}
}
}
public class JSONTask extends AsyncTask<String,String,String> {
@Override
protected String doInBackground(String... params) {
HttpURLConnection connection = null;
BufferedReader reader = null;
try {
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(stream));
StringBuffer buffer = new StringBuffer();
String line = "";
while ((line = reader.readLine()) != null) {
buffer.append(line);
}
String finalJson = buffer.toString();
JSONObject ParentObject = new JSONObject(finalJson);
JSONArray ParentArray = ParentObject.getJSONArray("");
for(int i=0; i<ParentArray.length();i++) {
JSONObject finalObject = ParentArray.getJSONObject(i);
String subject = finalObject.getString("subject");
Integer lessonNo = finalObject.getInt("lessonNo");
String lessonName = finalObject.getString("lessonName");
}
//return lessonName;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
}
}
}
字符串.xml
<resources>
<string name="app_name">VideoApp</string>
<string name="action_settings">Settings</string>
<string name="title_activity_second">SecondActivity</string>
<string name="title_activity_third">ThirdActivity</string>
<string-array name="subjects">
<item>Chemistry</item>
<item>Physics</item>
</string-array>
<string-array name="Physics">
<item>1. Measurement</item>
<item>2. Mechanics</item>
<item>3. Oscillations and Waves</item>
<item>4. Thermal Physics</item>
<item>5. Gravitational Field</item>
<item>6. Electrostatic Field</item>
<item>7. Magnetic Field</item>
<item>8. Current Electricity</item>
<item>9. Electronics</item>
<item>10. Mechanical Properties of Matter</item>
<item>11. Matter and Radiation</item>
</string-array>
<string-array name="Chemistry">
<item>1. Atomic structure</item>
<item>2. Structure and bonding</item>
<item>3. Chemical calculations</item>
<item>4. Gaseous state of matter</item>
<item>5. Energetics</item>
<item>6. Chemistry of s,p and d block elements</item>
<item>7. Basic concepts of organic chemistry</item>
<item>8. Hydrocarbons and halohydrocarbons</item>
<item>9. Oxygen containing organic compounds</item>
<item>10. Chemical kinetics</item>
<item>11. Equilibrium</item>
<item>12. Electro chemistry</item>
<item>13. Industrial chemistry and Environmental pollution</item>
</string-array>
</resources>
根据您的网址“ http://alvideobackend.azurewebsites.net/lesson/Chemistry ”中的内容，您应该创建一个带有 4 个参数（_id、subject、lessonNo、lessonName）的 Lesson 类。然后你可以调用你的 API 并使用 Gson 解析结果，如下所示：
ArrayList<Lesson> lessonList = new ArrayList<>();
Gson gson = new Gson();
Type type = new TypeToken<ArrayList<Lesson>>(){}.getType();
lessonList = gson.fromJson(json, type);
然后，您可以创建一个自定义适配器，该适配器采用完整的课程数组列表或从您的课程数组列表中创建一个字符串数组列表，并使用您在示例中所做的通用 ArrayAdapter。
我希望这有帮助！
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