Android

Question

我在网上找到了这段代码，如果适用，我决定在我的应用程序上试用一下。单击该按钮时，当数据库中的所有数据都显示在列表视图中时，它应该显示 activity。

代码如下：

MainActivity.java

public class MainActivity extends ListActivity {

private ProgressDialog pDialog;

// URL to get contacts JSON
private static String url = "http://api.androidhive.info/contacts/";

// JSON Node names
private static final String TAG_CONTACTS = "contacts";
private static final String TAG_ID = "id";
private static final String TAG_NAME = "name";
private static final String TAG_EMAIL = "email";
private static final String TAG_ADDRESS = "address";
private static final String TAG_GENDER = "gender";
private static final String TAG_PHONE = "phone";
private static final String TAG_PHONE_MOBILE = "mobile";
private static final String TAG_PHONE_HOME = "home";
private static final String TAG_PHONE_OFFICE = "office";

// contacts JSONArray
JSONArray contacts = null;

// Hashmap for ListView
ArrayList<HashMap<String, String>> contactList;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main5);

    contactList = new ArrayList<HashMap<String, String>>();

    ListView lv = getListView();

    // Listview on item click listener
    lv.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            // getting values from selected ListItem
            String name = ((TextView) view.findViewById(R.id.name))
                    .getText().toString();
            String cost = ((TextView) view.findViewById(R.id.email))
                    .getText().toString();
            String description = ((TextView) view.findViewById(R.id.mobile))
                    .getText().toString();

            // Starting single contact activity
            Intent in = new Intent(getApplicationContext(),
                    SingleContactActivity.class);
            in.putExtra(TAG_NAME, name);
            in.putExtra(TAG_EMAIL, cost);
            in.putExtra(TAG_PHONE_MOBILE, description);
            startActivity(in);

        }
    });

    // Calling async task to get json
    new GetContacts().execute();
}

/**
 * Async task class to get json by making HTTP call
 * */
private class GetContacts extends AsyncTask<Void, Void, Void> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Showing progress dialog
        pDialog = new ProgressDialog(MainActivity5.this);
        pDialog.setMessage("Please wait...");
        pDialog.setCancelable(false);
        pDialog.show();

    }

    @Override
    protected Void doInBackground(Void... arg0) {
        // Creating service handler class instance
        ServiceHandler sh = new ServiceHandler();

        // Making a request to url and getting response
        String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);

        Log.d("Response: ", "> " + jsonStr);

        if (jsonStr != null) {
            try {
                JSONObject jsonObj = new JSONObject(jsonStr);

                // Getting JSON Array node
                contacts = jsonObj.getJSONArray(TAG_CONTACTS);

                // looping through All Contacts
                for (int i = 0; i < contacts.length(); i++) {
                    JSONObject c = contacts.getJSONObject(i);

                    String id = c.getString(TAG_ID);
                    String name = c.getString(TAG_NAME);
                    String email = c.getString(TAG_EMAIL);
                    String address = c.getString(TAG_ADDRESS);
                    String gender = c.getString(TAG_GENDER);

                    // Phone node is JSON Object
                    JSONObject phone = c.getJSONObject(TAG_PHONE);
                    String mobile = phone.getString(TAG_PHONE_MOBILE);
                    String home = phone.getString(TAG_PHONE_HOME);
                    String office = phone.getString(TAG_PHONE_OFFICE);

                    // tmp hashmap for single contact
                    HashMap<String, String> contact = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    contact.put(TAG_ID, id);
                    contact.put(TAG_NAME, name);
                    contact.put(TAG_EMAIL, email);
                    contact.put(TAG_PHONE_MOBILE, mobile);

                    // adding contact to contact list
                    contactList.add(contact);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        } else {
            Log.e("ServiceHandler", "Couldn't get any data from the url");
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        // Dismiss the progress dialog
        if (pDialog.isShowing())
            pDialog.dismiss();
        /**
         * Updating parsed JSON data into ListView
         * */
        ListAdapter adapter = new SimpleAdapter(
                MainActivity5.this, contactList,
                R.layout.list_item, new String[] { TAG_NAME, TAG_EMAIL,
                        TAG_PHONE_MOBILE }, new int[] { R.id.name,
                        R.id.email, R.id.mobile });

        setListAdapter(adapter);
    }

}

}

然后是按钮所在的class：

public class MainActivity3Activity extends Activity implements OnClickListener {

Button ViewGradesActivity;
Button ClassScheduleActivity;
Button CalendarOfActivitiesActivity;
Button AccountBalanceActivity;
Button StudentProfileActivity;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_activity3);


   ShowMainActivity= (Button) findViewById(R.id.mainactbutton);
   ShowMainActivity.setOnClickListener(this);

   ClassScheduleActivity = (Button) findViewById(R.id.classSched);
   ClassScheduleActivity.setOnClickListener(this);

    CalendarOfActivitiesActivity = (Button)   findViewById(R.id.activities);
    CalendarOfActivitiesActivity.setOnClickListener(this);

    AccountBalanceActivity = (Button) findViewById(R.id.balance);
    AccountBalanceActivity.setOnClickListener(this);

    StudentProfileActivity = (Button) findViewById(R.id.profile);
    StudentProfileActivity.setOnClickListener(this);

}

@Override
public void onClick(View view) {
    switch(view.getId()) {
        //this is to show the activity with the list view
        case R.id.mainactbutton:
            startActivity(new Intent(this,MainActivity5.class));
            break;
        case R.id.classSched:
            startActivity(new Intent(this,classSchedule.class));
            break;
        case R.id.activities:
            startActivity(new Intent(this,CalendarOfActivities.class));
            break;
        case R.id.balance:
            startActivity(new Intent(this,AccountBalance.class));
            break;
        case R.id.profile:
            startActivity(new Intent(this,StudentProfile.class));
            break;
    }
}

}

所以每当我点击 mainactbutton 应用程序崩溃。我应该怎么办？列表视图的 activity 有问题吗？

感谢您的帮助。

编辑：现在我已经编辑了清单文件并添加了 MainActivity5 应用程序仍然崩溃，这是日志：

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
        at android.app.ListActivity.onContentChanged(ListActivity.java:243)
        at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:277)
        at android.app.Activity.setContentView(Activity.java:1881)
        at com.example.kreshiathea.myfirstapp.MainActivity5.onCreate(MainActivity5.java:52)
        at android.app.Activity.performCreate(Activity.java:5122)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)

这是我的列表视图：

activity_main5.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<!-- Main ListView 
     Always give id value as list(@android:id/list)
-->
<ListView
    android:id="@android:id/list"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"/>

</LinearLayout>

Answer 1

将您的代码更改为

this.startActivity(new Intent(this,MainActivity5.class));

& 你在你的 AndroidManifest.xml 中声明了这个 activity 了吗？

Answer 2

您必须在 AdnroidManifest.xml 文件

中声明 MainActivity5 class

如果您从 ListActivity 扩展，则不要使用 setContentView()。您需要通过 getListView() 获取默认列表视图。

Listview listview=getListView();

<ListView
 android:id="@android:id/list" 
 android:layout_width="match_parent" 
 android:layout_height="match_parent"/>

Answer 3

have you declared this activity in your AndroidManifest.xml?

您使用的每个 activity 都必须在清单中声明

      <activity
        android:name="com.example.kreshiathea.myfirstapp.MainActivity5"
        android:label="@string/app_name"
        android:id="@android:id/list"
        >
      </activity>

Android - 单击按钮以使用列表视图显示 activity 时应用程序崩溃

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