Java 无法调用方法
我正在尝试在我的程序中实现ZXing条形码扫描仪。在获得扫描结果后,我想将结果解析为一个名为Java 无法调用方法,java,android,eclipse,Java,Android,Eclipse,我正在尝试在我的程序中实现ZXing条形码扫描仪。在获得扫描结果后,我想将结果解析为一个名为getData()的方法,该方法属于另一个Java类。IDE上没有语法错误,但是无论发生什么情况,mysql.getData(contents)都不会调用该方法。请告知 如果我将此代码置于onCreate下,则整个程序强制关闭: package com.posQR.ip; import com.posQR.ip.MySQL; import android.app.Activity; import an
getData()
的方法,该方法属于另一个Java类。IDE上没有语法错误,但是无论发生什么情况,mysql.getData(contents)
都不会调用该方法。请告知
如果我将此代码置于onCreate
下,则整个程序强制关闭:
package com.posQR.ip;
import com.posQR.ip.MySQL;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class PosQRActivity extends Activity{
MySQL mysql;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mysql.getData("productID");
Button button = (Button)findViewById(R.id.button1);
button.setOnClickListener(scanListener);
}
public void onActivityResult(int requestCode, int resultCode, Intent intent) {
TextView textView = (TextView)findViewById(R.id.textView1);
if (requestCode == 0) {
if (resultCode == RESULT_OK) {
try {
String contents = intent.getStringExtra("SCAN_RESULT");
Toast.makeText(getApplicationContext(), contents + "from main", Toast.LENGTH_LONG).show();
mysql.getData(contents);
String string = Double.toString(mysql.getPrice());
textView.setText(string);
}
catch (Exception e) {
Toast.makeText(getApplicationContext(), "Please scan on the product's QR Code.", Toast.LENGTH_LONG).show();
}
} else if (resultCode == RESULT_CANCELED) {
// Handle cancel
}
}
}
private OnClickListener scanListener = new OnClickListener() {
public void onClick(View v) {
try{
Intent intent = new Intent("com.google.zxing.client.android.SCAN");
intent.putExtra("SCAN_MODE", "QR_CODE_MODE");
startActivityForResult(intent, 0);
}
catch (Exception e){
Toast.makeText(getApplicationContext(), "error opening scanner.", Toast.LENGTH_SHORT).show();
}
}
};
}
package com.posQR.ip;
导入java.io.BufferedReader;
导入java.io.InputStream;
导入java.io.InputStreamReader;
导入java.util.ArrayList;
导入org.apache.http.HttpEntity;
导入org.apache.http.HttpResponse;
导入org.apache.http.NameValuePair;
导入org.apache.http.client.HttpClient;
导入org.apache.http.client.entity.UrlEncodedFormEntity;
导入org.apache.http.client.methods.HttpPost;
导入org.apache.http.impl.client.DefaultHttpClient;
导入org.apache.http.message.BasicNameValuePair;
导入org.json.JSONArray;
导入org.json.JSONException;
导入org.json.JSONObject;
导入android.content.Context;
导入android.net.ParseException;
导入android.util.Log;
导入android.widget.Toast;
公共类MySQL{
双倍价格;
私有上下文localContext;
public void getData(字符串productID){
InputStream=null;
字符串结果=”;
Toast.makeText(localContext.getApplicationContext(),productID,Toast.LENGTH_LONG.show();
ArrayList nameValuePairs=新的ArrayList();
添加(新的BasicNameValuePair(“id”,productID));
//http post
试一试{
HttpClient HttpClient=新的DefaultHttpClient();
HttpPost HttpPost=新的HttpPost(“http://dl.dropbox.com/u/11233767/mysqlRequest.php");
setEntity(新的UrlEncodedFormEntity(nameValuePairs));
HttpResponse response=httpclient.execute(httppost);
HttpEntity=response.getEntity();
is=entity.getContent();
}捕获(例外e){
e(“Log_标记”,“http连接错误”+e.toString());
}
//将响应转换为字符串
试一试{
BufferedReader br=新的BufferedReader(新的InputStreamReader(is,“iso-8859-1”),8;
StringBuilder sb=新的StringBuilder();
字符串行=null;
而((line=br.readLine())!=null){
sb.追加(第+行“\n”);
}
is.close();
结果=sb.toString();
}捕获(例外e){
//TODO:处理异常
Toast.makeText(localContext.getApplicationContext(),“错误转换结果”,Toast.LENGTH\u LONG.show();
}
//配对数据
试一试{
JSONArray jArray=新JSONArray(结果);
JSONObject json_data=null;
json_data=jArray.getJSONObject(0);
Price=json_data.getDouble(“Price”);
}
捕获(JSONException e1){
Toast.makeText(localContext.getApplicationContext(),“找不到城市”,Toast.LENGTH\u LONG.show();
}捕获(解析异常e1){
e1.printStackTrace();
}
}
公开双价{
退货价格;
}
}
这里有很多问题,例如:
onCreate
中使用mysql
变量时,该变量为空,您必须声明它localContext
对象从未初始化,这将在调用getData()
时导致另一个NullPointerException
。您应该为MySql类创建一个接受上下文
对象的构造函数,并在解决第一个问题时使用该构造函数。或者,您可以将上下文对象传递给getData()
getData()
方法访问主/UI线程中的网络,这将导致另一个异常。在不同的线程中调用此方法,或者在方法本身中派生一个新线程。您可能希望使用异步任务logcat里有什么吗?你试过使用调试器吗?看起来你正在使用Android。如果是,请相应地标记它。我是否遗漏了什么,或者您甚至没有初始化您的
mysql
-字段?由于类中的方法不是静态的,因此需要类的对象。MySQL;嗨,我了解前两个,但不太了解数字3。从另一个类调用方法到底有什么问题?您是从同一个线程调用getData方法,该线程是负责UI的主线程。这不仅是一种糟糕的做法,而且Android实际上不会让你这么做。阅读这篇关于Android中线程的文章:
package com.posQR.ip;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.content.Context;
import android.net.ParseException;
import android.util.Log;
import android.widget.Toast;
public class MySQL{
double Price;
private Context localContext;
public void getData(String productID) {
InputStream is = null;
String result = "";
Toast.makeText(localContext.getApplicationContext(), productID, Toast.LENGTH_LONG).show();
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("id",productID));
//http post
try{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://dl.dropbox.com/u/11233767/mysqlRequest.php");
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
Log.e("log_tag", "Error in http connection"+e.toString());
}
//convert response to string
try {
BufferedReader br = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = br.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
} catch (Exception e) {
// TODO: handle exception
Toast.makeText(localContext.getApplicationContext(), "Error converting result.", Toast.LENGTH_LONG).show();
}
//paring data
try{
JSONArray jArray = new JSONArray(result);
JSONObject json_data=null;
json_data = jArray.getJSONObject(0);
Price=json_data.getDouble("price");
}
catch(JSONException e1){
Toast.makeText(localContext.getApplicationContext(), "No City Found" ,Toast.LENGTH_LONG).show();
} catch (ParseException e1) {
e1.printStackTrace();
}
}
public double getPrice(){
return Price;
}
}