我一直在使用this tutorial来了解JSON，PHP和MySQL如何协同工作。我已经很好了，因为我可以向数据库添加行，我可以从我的LogCat中看到我也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AllProductsActitivy.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那里得到了这个，不知道它意味着什么：
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
我无法弄清楚它为什么不起作用。正如我上面所说，我可以看到JSON正在工作，因为它在LogCat中显示，但没有任何显示。
对你们来说显而易见的事情？
谢谢！
答案 0 :(得分：2)
您错误地在代码中定义了private static final String TAG_PRODUCTS = "products";的密钥。
在您的JSON响应中，它将数组作为product而不是products发送。这就是解析响应时抛出错误的原因。 org.json.JSONException: No value for products
<强>编辑：
更改您的密钥如下：
// 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";
答案 1 :(得分：0)
尝试在setListAdapter之后调用adapter.notifyDataSetChanged（）。
来自Android文档：
<强> notifyDataSetChanged（）
通知附加的观察者基础数据已被更改，反映数据集的任何视图都应自行刷新。