我正在学习AsyncTask类和下面的例子来练习。我有一个UI有一个EditText(用于数据输入),一个有5个单选按钮的radiogroup和一个按钮(提交)。这个想法是当用户选择单选按钮并为EDITTEXT输入一个值时。按下按钮后,信息将转到数据库表。数据库表被创建并且整个代码工作。但是我想用AsyncTask在后台运行数据库操作函数。应用AsyncTask类后出现问题。请帮帮我。SQlite数据库操作和AsyncTask
这里是代码工作没有的AsyncTask:
package jhapps.com.myspending;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Toast;
public class Child extends AppCompatActivity {
private static Button btnsubmit;
private static RadioGroup rgChild;
private static RadioButton rbChild;
private static EditText dollarAmount;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_child);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
DataSubmitChild();
}
private void DataSubmitChild(){
btnsubmit=(Button)findViewById(R.id.btnSubmitChild);
btnsubmit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
rgChild = (RadioGroup) findViewById(R.id.rgChildren);
int selectedRbChild = rgChild.getCheckedRadioButtonId();
rbChild = (RadioButton) findViewById(selectedRbChild);
String rbChildF = rbChild.getText().toString();
dollarAmount = (EditText) findViewById(R.id.amountEnterChild);
String dollarAmountF = dollarAmount.getText().toString();
float dollarAmountFloat = Float.parseFloat(dollarAmountF);
DataBaseHelper dataBaseHelper = new DataBaseHelper(Child.this);
if (dollarAmountFloat != 0 & rbChildF != "") {
int itemID;
switch (rbChildF) {
case "Daycare":itemID=53;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
case "Lessons and Activities": itemID=54;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
case "Allowance":itemID=55;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
case "School Supplies and Fees" :itemID=56;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
case "Babysitting":itemID=57;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
}
Toast.makeText(Child.this,"Your spending is recorded!",Toast.LENGTH_LONG).show();
dollarAmount.setText("");
rgChild.clearCheck();
}else
Toast.makeText(Child.this,"Please choose an Item",Toast.LENGTH_LONG).show();
}
});
}
}
这里是用的AsyncTask代码没有工作:
package jhapps.com.myspending;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Toast;
public class Child extends AppCompatActivity {
private static Button btnsubmit;
private static RadioGroup rgChild;
private static RadioButton rbChild;
private EditText dollarAmount;
Context ctx;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_child);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
//DataSubmitChild();
rgChild = (RadioGroup) findViewById(R.id.rgChildren);
int selectedRbChild = rgChild.getCheckedRadioButtonId();
rbChild = (RadioButton) findViewById(selectedRbChild);
dollarAmount = (EditText) findViewById(R.id.amountEnterChild);
btnsubmit=(Button)findViewById(R.id.btnSubmitChild);
btnsubmit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
BackgroundTask backgroundTask=new BackgroundTask();
backgroundTask.execute();
}
});
dollarAmount.setText("");
rgChild.clearCheck();
}
private class BackgroundTask extends AsyncTask<Void,Void,Void>{
String rbChildF = rbChild.getText().toString();
String dollarAmountF = dollarAmount.getText().toString();
float dollarAmountFloat = Float.parseFloat(dollarAmountF);
@Override
protected Void doInBackground(Void... params) {
DataBaseHelper dataBaseHelper = new DataBaseHelper(getBaseContext());
if (dollarAmountFloat != 0 & rbChildF != "") {
int itemID;
switch (rbChildF) {
case "Daycare":itemID=53;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
case "Lessons and Activities": itemID=54;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
case "Allowance":itemID=55;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
case "School Supplies and Fees" :itemID=56;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
case "Babysitting":itemID=57;
dataBaseHelper.insertDataSpending(itemID, dollarAmountFloat);
break;
}
Toast.makeText(Child.this,"Your spending is recorded!",Toast.LENGTH_LONG).show();
}else
Toast.makeText(Child.this,"Please choose an Item",Toast.LENGTH_LONG).show();
return null;
}
} }
这里是错误信息:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: jhapps.com.myspending, PID: 27613
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.widget.RadioButton.getText()' on a null object reference
at jhapps.com.myspending.Child$BackgroundTask.<init>(Child.java:62)
at jhapps.com.myspending.Child$BackgroundTask.<init>(Child.java:0)
at jhapps.com.myspending.Child$2.onClick(Child.java:54)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
很多很多谢谢!这是一个很大的帮助!它有助于我理解这个概念。 –