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我一直在使用本教程来学习 JSON、PHP 和 MySQL 如何协同工作。我做得很好，因为我可以向数据库中添加行，而且我可以从我的 LogCat 中看到我还可以显示数据库中的所有行。问题是 ListView 根本没有显示任何内容。只是黑色。

这是我的 all_products.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>

这是我的 list_item.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="wrap_content"
android:orientation="vertical">

<!-- Product id (pid) - will be HIDDEN - used to pass to other activity -->
<TextView
    android:id="@+id/pid"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:visibility="gone" />

<!-- Name Label -->
<TextView
    android:id="@+id/name"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:paddingTop="6dp"
    android:paddingLeft="6dp"
    android:textSize="17sp"
    android:textStyle="bold"/>

</LinearLayout>

这是我的 AllProductsActivity.java：

public class AllProductsActivity extends ListActivity {
 
// Progress Dialog
private ProgressDialog pDialog;

// Creating JSON Parser object
JSONParser jParser = new JSONParser();

ArrayList<HashMap<String, String>> productsList;

// url to get all products list
private static String url_all_products = "http://81.xxx.xxx.xxx/get_all_products.php";

// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCTS = "products";
private static final String TAG_PID = "pid";
private static final String TAG_NAME = "name";

// products JSONArray
JSONArray products = null;

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

    // Hashmap for ListView
    productsList = new ArrayList<HashMap<String, String>>();

    // Loading products in Background Thread
    new LoadAllProducts().execute();

    // Get listview
    ListView lv = getListView();

    // on seleting single product
    // launching Edit Product Screen
    lv.setOnItemClickListener(new OnItemClickListener() {

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

            // Starting new intent
            Intent in = new Intent(getApplicationContext(),
                    EditProductActivity.class);
            // sending pid to next activity
            in.putExtra(TAG_PID, pid);

            // starting new activity and expecting some response back
            startActivityForResult(in, 100);
        }
    });

}

// Response from Edit Product Activity
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    // if result code 100
    if (resultCode == 100) {
        // if result code 100 is received
        // means user edited/deleted product
        // reload this screen again
        Intent intent = getIntent();
        finish();
        startActivity(intent);
    }

}

/**
 * Background Async Task to Load all product by making HTTP Request
 * */
class LoadAllProducts extends AsyncTask<String, String, String> {

    /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(AllProductsActivity.this);
        pDialog.setMessage("Loading products. Please wait...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();
    }

    /**
     * getting All products from url
     * */
    protected String doInBackground(String... args) {
        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        // getting JSON string from URL
        JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);

        // Check your log cat for JSON reponse
        Log.d("All Products: ", json.toString());

        try {
            // Checking for SUCCESS TAG
            int success = json.getInt(TAG_SUCCESS);

            if (success == 1) {
                // products found
                // Getting Array of Products
                products = json.getJSONArray(TAG_PRODUCTS);

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

                    // Storing each json item in variable
                    String id = c.getString(TAG_PID);
                    String name = c.getString(TAG_NAME);

                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    map.put(TAG_PID, id);
                    map.put(TAG_NAME, name);

                    // adding HashList to ArrayList
                    productsList.add(map);
                }
            } else {
                // no products found
                // Launch Add New product Activity
                Intent i = new Intent(getApplicationContext(),
                        NewProductActivity.class);
                // Closing all previous activities
                i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(i);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }

        return null;
    }

    /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute(String file_url) {
        // dismiss the dialog after getting all products
        pDialog.dismiss();
        // updating UI from Background Thread
        runOnUiThread(new Runnable() {
            public void run() {
                /**
                 * Updating parsed JSON data into ListView
                 * */
                ListAdapter adapter = new SimpleAdapter(
                        AllProductsActivity.this, productsList,
                        R.layout.list_item, new String[] { TAG_PID,
                                TAG_NAME},
                        new int[] { R.id.pid, R.id.name });
                // updating listview
                setListAdapter(adapter);
            }
        });

    }

}
}

我也从 LogCat 得到这个，不知道它是什么意思：

10-10 17:09:00.235: W/System.err(20177): org.json.JSONException: No value for products
10-10 17:09:00.255: W/System.err(20177): at org.json.JSONObject.get(JSONObject.java:354)
10-10 17:09:00.255: W/System.err(20177): at org.json.JSONObject.getJSONArray(JSONObject.java:544)
10-10 17:09:00.255: W/System.err(20177): at com.sandtdevelopment.testjson.AllProductsActivity$LoadAllProducts.doInBackground(AllProduct    sActivity.java:139)
10-10 17:09:00.255: W/System.err(20177): at com.sandtdevelopment.testjson.AllProductsActivity$LoadAllProducts.doInBackground(AllProduct    sActivity.java:1)
10-10 17:09:00.255: W/System.err(20177): at android.os.AsyncTask$2.call(AsyncTask.java:287)
10-10 17:09:00.255: W/System.err(20177): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
10-10 17:09:00.255: W/System.err(20177): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
10-10 17:09:00.255: W/System.err(20177): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
10-10 17:09:00.255: W/System.err(20177): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
10-10 17:09:00.255: W/System.err(20177): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
10-10 17:09:00.260: W/System.err(20177): at java.lang.Thread.run(Thread.java:856)
10-10 17:09:00.570: E/SpannableStringBuilder(20177): SPAN_EXCLUSIVE_EXCLUSIVE spans   cannot have a zero length
10-10 17:09:00.570: E/SpannableStringBuilder(20177): SPAN_EXCLUSIVE_EXCLUSIVE spans   cannot have a zero length

我真的不知道为什么它不起作用。正如我上面所说，我可以看到 JSON 正在工作，因为它显示在 LogCat 中，但没有显示任何内容。

你们有什么明显的吗？

谢谢！

4

2 回答 2

2

您在代码中错误地定义了键private static final String TAG_PRODUCTS = "products";。

在您的 JSON 响应中，它将数组发送为 productnot products。这就是为什么在解析响应时抛出错误。org.json.JSONException: No value for products

编辑：

如下更改您的密钥：

// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCTS = "test1";
private static final String TAG_PID = "PID";
private static final String TAG_NAME = "name";
于 2013-10-10T15:20:22.957 回答
0

尝试在 setListAdapter 之后调用 adapter.notifyDataSetChanged()。

来自 Android 文档：

notifyDataSetChanged()

通知附加的观察者底层数据已更改，任何反映数据集的视图都应自行刷新。

于 2013-10-10T15:16:27.280 回答