【发布时间】：2016-07-07 15:18:22
【问题描述】：
我对创建 Android 应用程序非常陌生，我正在使用 Android Studio 来处理我的项目。我正在从我的数据库中获取 json 结果，并且获取的结果是我想要的，但我不知道如何让 asynctask 在 onCreate 之前完成。我的 ListView 是空的，但我通过调试器确认我的 asynctask 结果值存在。
更新：我跟踪错误到这里：
public void populatedata(){
/**get back result from pref**/
SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", MODE_PRIVATE);
String result =pref.getString("result", "null");
try{
Log.d("ADebugTag", "Value: "+result);
JSONObject person = new JSONObject(result);
JSONArray jsonMainNode = person.getJSONArray("result");
final int n = jsonMainNode.length();
ListView lv= (ListView)findViewById(R.id.listView1);
String[] from = new String[] {"id", "time"};
int[] to = new int[] {android.R.id.text1};
List<Map<String,String>> classList = new ArrayList<Map<String,String>>();
// for(int i = 0; i< n; i++){
//HashMap<String, String> map = new HashMap<String, String>();
// JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);
// String id = jsonChildNode.getString("id");
// String schedule = jsonChildNode.getString("schedule");
// String time = jsonChildNode.getString("time");
// String output = schedule + time;
// classList.add(createchild(id,output));
// Log.d("ADebugTag", "Value before loop: "+classList);
// }
// Log.d("ADebugTag", "Value after loop: "+classList);
Log.d("ADebugTag", "Hi, Im here5");
for(int i = 0; i < 10; i++){
HashMap<String, String> map = new HashMap<String, String>();
map.put("id", "time" + i);
map.put("col_1", "col_1_item_" + i);
map.put("col_2", "col_2_item_" + i);
map.put("col_3", "col_3_item_" + i);
classList.add(map);
}
SimpleAdapter simpleAdapter = new SimpleAdapter(this,classList, android.R.layout.simple_list_item_1, from, to);
lv.setAdapter(simpleAdapter);
}
catch(JSONException e){
Toast.makeText(getApplicationContext(), "Error"+e.toString(), Toast.LENGTH_SHORT).show();
}
}
private HashMap<String, String>createchild(String id,String output){
HashMap<String,String> childNo = new HashMap<String,String>();
childNo.put(id,output);
Log.d("ADebugTag", "Hi, Im here4");
return childNo;
}
the // for loop is the one i wanna work it out, and my string result `is{"result":[{"id":"00000000001","schedule":"000001","time":"10:21:37"}]}`
updated: It's my mistake, I did not create a R.layout and textview for it, I learned to use custom adapter and create an external layout.
public class ViewClassActivity extends AppCompatActivity{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_view_class);
/**prepare list**/
SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", MODE_PRIVATE);
String id =pref.getString("userid", "null");
Log.d("ADebugTag", "Hi, Im here");
new fetchclass(this,id).execute(id);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
public void getdata(String result){
//save preferences
SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", MODE_PRIVATE);
SharedPreferences.Editor editor = pref.edit();
editor.putString("result", result); // Saving result string
Log.d("ADebugTag", "Hi, Im here3");
// Save the changes in SharedPreferences
editor.apply(); // apply changes
populatedata();
Log.d("ADebugTag", "Hi, Im here6");
}
public void populatedata(){
/**get back result from pref**/
SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", MODE_PRIVATE);
String result =pref.getString("result", "null");
Log.d("ADebugTag",result);
try{
Log.d("ADebugTag", "Value: "+result);
JSONObject person = new JSONObject(result);
JSONArray jsonMainNode = person.getJSONArray("result");
final int n = jsonMainNode.length();
ListView lv= (ListView)findViewById(R.id.listView1);
String[] from = new String[] {"id", "schedule"};
int[] to = new int[] {R.id.textView20,R.id.textView21};
//List<Map<String,String>> classList = new ArrayList<Map<String,String>>();
ArrayList<HashMap<String,String>> classList = new ArrayList<>();
for(int i = 0; i< n; i++){
HashMap<String, String> hashMap = new HashMap<>();
JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);
String id = jsonChildNode.getString("id");
String schedule = jsonChildNode.getString("schedule");
String time = jsonChildNode.getString("time");
String output = schedule + time;
hashMap.put("id", id);
hashMap.put("schedule", output);
classList.add(hashMap);
//classList.add(createchild(id,output));
Log.d("ADebugTag", "Value before loop: "+classList);
}
CustomAdapter simpleAdapter = new CustomAdapter(this,classList, R.layout.list_view_item, from, to);
lv.setAdapter(simpleAdapter);
}
catch(JSONException e){
Toast.makeText(getApplicationContext(), "Error"+e.toString(), Toast.LENGTH_SHORT).show();
}
}
private HashMap<String, String>createchild(String id,String output){
HashMap<String,String> childNo = new HashMap<String,String>();
childNo.put(id,output);
Log.d("ADebugTag", "Hi, Im here4");
return childNo;
}
list_view_item.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin">
<TextView
android:id="@+id/textView20"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:padding="@dimen/activity_horizontal_margin"
android:text="Demo1"
android:textColor="#000" />
<TextView
android:id="@+id/textView21"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:padding="@dimen/activity_horizontal_margin"
android:text="Demo2"
android:textColor="#000"
android:layout_alignParentTop="true"
android:layout_toRightOf="@+id/textView20"
android:layout_toEndOf="@+id/textView20" />
</RelativeLayout>
自定义适配器
public class CustomAdapter extends SimpleAdapter {
LayoutInflater inflater;
Context context;
ArrayList<HashMap<String, String>> arrayList;
public CustomAdapter(Context context, ArrayList<HashMap<String, String>> data, int resource, String[] from, int[] to) {
super(context, data, resource, from, to);
this.context = context;
this.arrayList = data;
inflater.from(context);
}
}
在使用这个网站时发现了我的问题，感谢大家的帮助：
【问题讨论】：
-
因为当执行异步时，后台线程启动（使用 onPost() 发布结果）并且程序移至下一行......而且我可以看到您的列表视图甚至在后台任务之前填充了适配器已完成...我建议的一个解决方案是在您的任务完成后设置适配器，即在您的
getdata(String result)中的populatedata();之后调用SimpleAdapter simpleAdapter = new SimpleAdapter(this,classList, android.R.layout.simple_list_item_1, new String[] {"result"}, new int[] {android.R.id.text1}); listView.setAdapter(simpleAdapter);并检查结果 -
@Mohit 你的推荐作品！我的调试器现在告诉我代码运行我想要的序列！但我仍然面临空列表视图！可能是生成hasmap的原因吗？我获得的字符串值为 {"result":[{"id":"00000000001","schedule":"000001","time":"10:21:37"}]}但是在 hasmap 之后它是 [{00000000001=00000110:21:37}] 并且顺便说一下在下面发布您的答案，以便我可以将其标记为勾号，尽管我的列表视图仍然存在，但您解决了我最基本的问题空白
-
第一：请更新代码以便分析...... 第二：是，你是对的，每次你在循环中调用
createchild()时，你都在初始化hashmap，你会得到新的空hashmap..只需声明全局hashmap变量并初始化一次（比如在onCreate（）或某个地方但不在循环中）并在方法中调用它......希望它有帮助 -
但我认为我的 hasmap 方法不在循环中？还是您的意思是这部分？
String time = jsonChildNode.getString("time"); String output = schedule + time; classList.add(createchild(id,output)); Log.d("ADebugTag", "Value: "+classList); }将 createchild(id,output)); 带出循环？但是，怎么做？ -
只需从
createchild()中删除HashMap<String,String> childNo = new HashMap<String,String>();并将其放在班级顶部，即低于List<Map<String,String>> classList = new ArrayList<Map<String,String>>();
标签： android listview android-asynctask simpleadapter