我想获取位于id外部存储中的数据库中列中的数据，并将其与id来自 Internet 的数据库中的列进行比较。从互联网下载数据库已经完成。我唯一的问题是我无法比较这两个值。我创建了从数据库中获取数据的代码：
try {
int ct_id;
String ct_name;
try{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://10.0.2.2/city.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 reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line="0";
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
//paring data
int max = 0;
try{
jArray = new JSONArray(result);
JSONObject json_data=null;
for(int i=0;i<jArray.length();i++){
json_data = jArray.getJSONObject(i);
ct_id=json_data.getInt("max(id)");
ct_name=json_data.getString("date");
max = ct_id;
}
}catch(JSONException e1){
} catch (ParseException e1) {
e1.printStackTrace();
}
URL url2 = new URL("http://10.0.2.2/xampp/uindictionaryse/images/kamus.db");
final HttpURLConnection urlConnect = (HttpURLConnection) url2.openConnection();
HttpURLConnection urlConnection2 = urlConnect;
urlConnection2.setRequestMethod("GET");
urlConnection2.setDoOutput(true);
urlConnection2.connect();
final File file = new File("/data/data/com.raj.dse/databases/dse");
//and connect!
int idex = 0;
Cursor c = db.query("person", new String[] {"_id", "date"}, "max(id)", null, null, null, null);
startManagingCursor(c);
idex = c.getColumnIndex("_id");
if(idex>=max){
handler.post(new Runnable() {
@Override
public void run() {
state.setText("Database uptodate...");
}
});
}else{
Builder builder = new Builder(null);
builder.setTitle("Update"); // kalo ambil dari resources
builder.setMessage("Your Database is out of date, do you want update?"); //disini yang ditambahkan
//builder.setMessage("Exit Application?"); // ini yg di commentkan
builder.setPositiveButton("Yes", new DialogInterface.OnClickListener({
public void onClick(DialogInterface dialog, int which){
file.delete();
//this will be used to write the downloaded data into the file we created
FileOutputStream fileOutput = null;
try {
fileOutput = new FileOutputStream(file);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
//this will be used in reading the data from the internet
InputStream inputStream = null;
try {
inputStream = urlConnect.getInputStream();
} catch (IOException e) {
e.printStackTrace();
}
//this is the total size of the file
int totalSize = urlConnect.getContentLength();
//variable to store total downloaded bytes
int downloadedSize = 0;
//create a buffer...
byte[] buffer = new byte[1024];
int bufferLength = 0; //used to store a temporary size of the buffer
//now, read through the input buffer and write the contents to the file
try {
while ((bufferLength = inputStream.read(buffer)) > 0 ) {
//add the data in the buffer to the file in the file output stream (the file on the sd card
fileOutput.write(buffer, 0, bufferLength);
//add up the size so we know how much is downloaded
downloadedSize += bufferLength;
//this is where you would do something to report the prgress, like this maybe
// updateProgress(downloadedSize, totalSize);
}
} catch (IOException e) {
e.printStackTrace();
}
handler.post(new Runnable() {
@Override
public void run() {
state.setText("Database uptdated...");
}
});
try {
fileOutput.close();
} catch (IOException e) {
e.printStackTrace();
}
});
builder.setNegativeButton("No", null);
builder.create().show();
}
} catch (MalformedURLException e) {
Toast.makeText(SplashScreen.this, "Error incorrect specification", Toast.LENGTH_SHORT).show();
e.printStackTrace();
} catch (IOException e) {
Toast.makeText(SplashScreen.this, "Error occur", Toast.LENGTH_SHORT).show();
e.printStackTrace();
}
这是 LogCat 中的输出：
07-01 10:27:07.275: ERROR/AndroidRuntime(1024): FATAL EXCEPTION: Thread-10
07-01 10:27:07.275: ERROR/AndroidRuntime(1024): java.lang.NullPointerException
07-01 10:27:07.275: ERROR/AndroidRuntime(1024): at com.raj.dse.SplashScreen$1.run(SplashScreen.java:177)
07-01 10:27:07.275: ERROR/AndroidRuntime(1024): at java.lang.Thread.run(Thread.java:1019)
根据 LogCat，我在这里遇到了问题：
db.compileStatement(query);
我认为该陈述是正确的，但我不明白问题出在哪里。关于如何解决这个问题的任何建议？