android - 从 mysql 检索数据到 ListView 时应用程序崩溃

Question

我正在尝试从 mysql 检索数据并加载到 ListView 中。但是当我尝试运行它时应用程序崩溃了。我无法解决错误。JSON 响应工作正常并且结果显示在浏览器中.请帮助。这是 MainActivity 文件

    package com.example.triallistview;

    import java.io.BufferedReader;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import org.apache.http.HttpEntity;
    import org.apache.http.HttpResponse;
    import org.apache.http.client.HttpClient;
    import org.apache.http.client.entity.UrlEncodedFormEntity;
    import org.apache.http.client.methods.HttpPost;
    import org.apache.http.impl.client.DefaultHttpClient;
    import org.json.JSONArray;
    import org.json.JSONException;
    import org.json.JSONObject;

    import android.app.ListActivity;
    import android.net.ParseException;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.AdapterView.OnItemClickListener;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.Toast;

    public class MainActivity extends ListActivity {
int ct_id;
String[] ct_name = null;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    String result = null;
    InputStream is = null;
    StringBuilder sb = null;
    ListView lv;
    lv = (ListView)findViewById(R.id.list);
    // http post
    try {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost("http://127.0.0.1/example/city.php");
       // httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
        HttpResponse response = httpclient.execute(httppost);
        HttpEntity entity = response.getEntity();
        is = entity.getContent();
    } catch (Exception e) {
        Log.e("log_tag", "Error in http connection" + e.toString());
    }
    // convert response to string
    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        sb = new StringBuilder();
        sb.append(reader.readLine() + "\n");
        String line = "0";
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        result = sb.toString();
    } catch (Exception e) {
        Log.e("log_tag", "Error converting result " + e.toString());
    }
    // paring data
    JSONArray jArray;
    try {
        jArray = new JSONArray(result);
        JSONObject json_data = null;
        ct_name = new String[jArray.length()];
        for (int i = 0; i < jArray.length(); i++) {
            json_data = jArray.getJSONObject(i);
            ct_id = json_data.getInt("CITY_ID");
            ct_name[i] = json_data.getString("CITY_NAME");
        }
    } catch (JSONException e1) {
        Toast.makeText(getBaseContext(), "No City Found", Toast.LENGTH_LONG)
                .show();
    } catch (ParseException e1) {
        e1.printStackTrace();
    }


    lv = getListView();
    lv.setAdapter(new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, ct_name));
    lv.setTextFilterEnabled(true);
    lv.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(int  position, long id) {
            // When clicked, show a toast with the TextView text
            Toast.makeText(getApplicationContext(),
                    ct_name[position] + " wasClicked", Toast.LENGTH_SHORT)
                    .show();
        }

        @Override
        public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
                long arg3) {
            // TODO Auto-generated method stub

        }


    });
    }
     }

logcat 看起来像这样

    03-25 02:42:03.195: E/AndroidRuntime(2380): FATAL EXCEPTION: main
    03-25 02:42:03.195: E/AndroidRuntime(2380): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.triallistview/com.example.triallistview.MainActivity}: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.os.Handler.dispatchMessage(Handler.java:99)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.os.Looper.loop(Looper.java:137)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.ActivityThread.main(ActivityThread.java:5103)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at java.lang.reflect.Method.invokeNative(Native Method)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at java.lang.reflect.Method.invoke(Method.java:525)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at dalvik.system.NativeStart.main(Native Method)
    03-25 02:42:03.195: E/AndroidRuntime(2380): Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at  android.app.ListActivity.onContentChanged(ListActivity.java:243)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:270)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.Activity.setContentView(Activity.java:1895)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at com.example.triallistview.MainActivity.onCreate(MainActivity.java:34)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.Activity.performCreate(Activity.java:5133)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
    03-25 02:42:03.195: E/AndroidRuntime(2380):     ... 11 more

请建议我应该做什么更改。

Answer 1

Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'

你有

public class MainActivity extends ListActivity {

然后

setContentView(R.layout.activity_main);

所以你需要在 activity_main.xml 中有一个 ListView，其 id 如下所示

<ListView
android:id="@android:id/list"

同时移除

lv = (ListView)findViewById(R.id.list);

您可以使用lv = getListView()

引用文档

ListActivity has a default layout that consists of a single, full-screen list in the center of the screen. However, if you desire, you can customize the screen layout by setting your own view layout with setContentView() in onCreate(). To do this, your own view MUST contain a ListView object with the id "@android:id/list" (or list if it's in code)

除此之外，您还在主 ui 线程上执行网络操作。您需要使用 Thread 或 AsyncTask。

 HttpClient httpclient = new DefaultHttpClient();
 HttpPost httppost = new HttpPost("http://127.0.0.1/example/city.php");
 // httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
 HttpResponse response = httpclient.execute(httppost); // must be in a thread

您将得到 NetworkOnMainThreadException。

The exception that is thrown when an application attempts to perform a networking operation on its main thread.

This is only thrown for applications targeting the Honeycomb SDK or higher. Applications targeting earlier SDK versions are allowed to do networking on their main event loop threads, but it's heavily discouraged

编辑:

似乎有很多困惑。人们想要更准确的答案。所以我会发布一个例子

例子:

在下面我们有一个 TextView 和一个 ListView

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.testall.MainActivity"
    tools:ignore="MergeRootFrame" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="150dp"
        android:layout_marginTop="22dp"
        android:text="Static TextView" />

    <ListView
        android:id="@android:id/list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/textView1"
        android:layout_marginLeft="12dp"
        android:layout_marginTop="12dp" >
    </ListView>

</RelativeLayout>

主 Activity .java

此处 MainActivity 扩展了 ListActivity 并且您有 setContentView(R.layout.activity_main);。 activity_main.xml 除了 listview 之外还有其他 View 。

所以你需要一个在你的 xml 中带有 id android:id="@android:id/list" 的 ListView

public class MainActivity extends ListActivity {

    String[] array ={"A","B","C","D","E"};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView lv = getListView();
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,array);
        lv.setAdapter(adapter);

    }

}

快照

查看快照，它有一个静态 TextView 。

现在我更改了 id，如下所示。我的布局中仍然有 TextView 没有其他改变

<ListView
    android:id="@+id/list"

应用崩溃

 03-25 04:16:02.022: E/AndroidRuntime(1275): Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'

好吧，如果人们仍然不理解并说不清楚并投反对票，他们应该在评论中说明原因。我很乐意编辑。

如果您不希望显示默认列表以外的任何其他 View ，则无需 setContentView(R.layout.activity_main);。例如。

public class MainActivity extends ListActivity {

    String[] array ={"A","B","C","D","E"};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,array);
        setListAdapter(adapter);

    }

}

上面除了显示默认列表外，没有其他 View 。