Android AsyncTaskLoader Example with ListView and BaseAdapter
July 09, 2015
AsyncTaskLoader
android.content.AsyncTaskLoader<D> is a loader that usesAsyncTask to perform the task. It is an abstract class and to use it we need to extend and override its methods. In our example we will iterate a list using ListView. Find some methods that need to be overridden.
loadInBackground() : Performs actual task in background and returns the result.
onCanceled(D data) : This method is called if task is cancelled before completion. It is used to clean up data post cancellation.
cancelLoadInBackground() : We override this method to cancel the background process. If there is no process in background, it is not going to be called.
ListView
android.widget.ListView is a view which shows items in a vertically scrolling list. To achieve it we need to add ListView in layout.
<ListView
android:id="@+id/employees"
android:layout_height="match_parent"
android:layout_width="match_parent"/>
ListView employeeListView = (ListView) findViewById(R.id.employees); employeeListView.setAdapter(empAdapter);
BaseAdapter
android.widget.BaseAdapter is common implementation of adapters like ArrayAdapter<T>, CursorAdapter and SimpleAdapter.BaseAdapter can be used with ListView. To use BaseAdapter , we need to extend it in our class and override required methods. Some of them are given below.
View getView(int position, View view, ViewGroup parent) : Returns a view that displays data at specified position.
Object getItem(int position): Returns the data item for a given position.
long getItemId(int position): Returns the row id associated with the given position.
int getCount() : Count of data items represented by adapter.
Finally to display data, we need to call
notifyDataSetChanged().
Complete Example
Employee.java
package com.concretepage;
public class Employee {
public String empid;
public String name;
public Employee(String id, String name) {
this.empid = id;
this.name = name;
}
}
EmployeeLoader.java
package com.concretepage;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.support.v4.content.AsyncTaskLoader;
public class EmployeeLoader extends AsyncTaskLoader<List<Employee>> {
public EmployeeLoader(Context context) {
super(context);
}
@Override
public List<Employee> loadInBackground() {
List<Employee> list = new ArrayList<Employee>();
list.add(new Employee("emp1", "Brahma"));
list.add(new Employee("emp2", "Vishnu"));
list.add(new Employee("emp3", "Mahesh"));
return list;
}
}
EmployeeAdapter.java
package com.concretepage;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
public class EmployeeAdapter extends BaseAdapter {
private LayoutInflater inflater;
private List<Employee> employees = new ArrayList<Employee>();
public EmployeeAdapter(Context context, List<Employee> employees) {
this.employees = employees;
inflater = LayoutInflater.from(context);
}
@Override
public View getView(int position, View view, ViewGroup parent) {
Employee emp = (Employee) getItem(position);
if (view == null) {
view = inflater.inflate(R.layout.employeedata, null);
}
TextView empid = (TextView) view.findViewById(R.id.empid);
empid.setText(emp.empid);
TextView empname = (TextView) view.findViewById(R.id.empname);
empname.setText(emp.name);
return view;
}
@Override
public Object getItem(int position) {
return employees.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public int getCount() {
return employees.size();
}
public void setEmployees(List<Employee> data) {
employees.addAll(data);
notifyDataSetChanged();
}
}
MainActivity.java
package com.concretepage;
import java.util.ArrayList;
import java.util.List;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.Loader;
import android.widget.ListView;
public class MainActivity extends FragmentActivity implements LoaderManager.LoaderCallbacks<List<Employee>> {
EmployeeAdapter empAdapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
empAdapter = new EmployeeAdapter(this, new ArrayList<Employee>());
ListView employeeListView = (ListView) findViewById(R.id.employees);
employeeListView.setAdapter(empAdapter);
getSupportLoaderManager().initLoader(1, null, this).forceLoad();
}
@Override
public Loader<List<Employee>> onCreateLoader(int id, Bundle args) {
return new EmployeeLoader(MainActivity.this);
}
@Override
public void onLoadFinished(Loader<List<Employee>> loader, List<Employee> data) {
empAdapter.setEmployees(data);
}
@Override
public void onLoaderReset(Loader<List<Employee>> loader) {
empAdapter.setEmployees(new ArrayList<Employee>());
}
}
employeedata.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:background="#D1C4E9">
<TextView
android:id="@+id/empid"
android:textSize="25sp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="#FF8A80"
android:layout_weight="2"/>
<TextView
android:id="@+id/empname"
android:textSize="25sp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="#FF8A80"
android:layout_weight="2"/>
</LinearLayout>
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#C98C00">
<ListView
android:id="@+id/employees"
android:layout_height="match_parent"
android:layout_width="match_parent"/>
</LinearLayout>
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.concretepage"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk android:minSdkVersion="11"/>
<application
android:allowBackup ="false"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name" >
<activity android:name=".MainActivity" android:theme="@android:style/Theme.NoTitleBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
Output
