我的应用在启动后立即崩溃。我不知道为什么。我在此应用程序中遇到其他问题，这些问题已在另一个线程中解决，但是，我现在遇到的问题完全不同。我知道我的代码/结构不是最优雅，但是在涉及Android和XML时我仍然是一个新手。
这是日志错误stacktrace:
11-30 15:42:46.970: W/dalvikvm(10028): threadid=1: thread exiting with uncaught exception (group=0x40d04210)
11-30 15:42:46.970: E/AndroidRuntime(10028): FATAL EXCEPTION: main
11-30 15:42:46.970: E/AndroidRuntime(10028): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.defsoftsol.db.check/com.defsoftsol.db.check.MainActivity}: java.lang.NullPointerException
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1880)
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.app.ActivityThread.access$600(ActivityThread.java:123)
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.os.Handler.dispatchMessage(Handler.java:99)
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.os.Looper.loop(Looper.java:137)
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.app.ActivityThread.main(ActivityThread.java:4428)
11-30 15:42:46.970: E/AndroidRuntime(10028): at java.lang.reflect.Method.invokeNative(Native Method)
11-30 15:42:46.970: E/AndroidRuntime(10028): at java.lang.reflect.Method.invoke(Method.java:511)
11-30 15:42:46.970: E/AndroidRuntime(10028): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:787)
11-30 15:42:46.970: E/AndroidRuntime(10028): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554)
11-30 15:42:46.970: E/AndroidRuntime(10028): at dalvik.system.NativeStart.main(Native Method)
11-30 15:42:46.970: E/AndroidRuntime(10028): Caused by: java.lang.NullPointerException
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.app.Activity.findViewById(Activity.java:1794)
11-30 15:42:46.970: E/AndroidRuntime(10028): at com.defsoftsol.db.check.MainActivity.<init>(MainActivity.java:43)
11-30 15:42:46.970: E/AndroidRuntime(10028): at java.lang.Class.newInstanceImpl(Native Method)
11-30 15:42:46.970: E/AndroidRuntime(10028): at java.lang.Class.newInstance(Class.java:1319)
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
11-30 15:42:46.970: E/AndroidRuntime(10028): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1871)
11-30 15:42:46.970: E/AndroidRuntime(10028): ... 11 more
这是我完整的代码:
public class MainActivity extends Activity {
String deviceID="",dateStamp="",buff="",db_id="",db_device_id="",db_install_date="";
byte[] data;
HttpPost httppost;
StringBuffer buffer;
HttpResponse response;
HttpClient httpclient;
InputStream inputStream;
List<NameValuePair> nameValuePairs;
int ID,activeinstalls;
long diff;
TableLayout tl=(TableLayout)findViewById(R.id.db_data);
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button refresh = (Button)findViewById(R.id.btnrefresh);
refresh.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
new MyAsyncTask(MainActivity.this).execute();
}
});
}
@SuppressWarnings("unused")
public class MyAsyncTask extends AsyncTask<Void, Void, Void>
{
ProgressDialog mProgressDialog;
private Context context;
public MyAsyncTask(Context context) {
this.context = context;
}
@Override
protected void onPostExecute(Void result) {
mProgressDialog.dismiss();
}
@Override
protected void onPreExecute() {
mProgressDialog = ProgressDialog.show(MainActivity.this, "Loading...", "Data is Loading...");
}
@Override
protected Void doInBackground(Void... params) {
update();
return null;
}
}
private final SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
private final long ONE_DAY = 24 * 60 * 60 * 1000;
@SuppressWarnings("unused")
public void update()
{
int activeinstalls = 0;
Date now = new Date();
dateStamp = formatter.format(now);
runOnUiThread(new Runnable(){
@Override
public void run(){
UISetup();
}
});
ID = 1;
try
{
do
{
try
{
httpclient = new DefaultHttpClient();
httppost = new HttpPost("http://#.#.#.#/***.php"); //Address hidden for server security.
nameValuePairs = new ArrayList<NameValuePair>(1);
nameValuePairs.add(new BasicNameValuePair("_id", String.valueOf(ID)));
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
response = httpclient.execute(httppost);
inputStream = response.getEntity().getContent();
data = new byte[256];
buffer = new StringBuffer();
int len = 0;
while (-1 != (len = inputStream.read(data)) )
{
buffer.append(new String(data, 0, len));
}
inputStream.close();
} catch (Exception e) {
Toast.makeText(MainActivity.this, "error"+e.toString(), Toast.LENGTH_LONG).show();
e.printStackTrace();
}
if(buffer.charAt(0)=='Y')
{
ID++;
buff = buffer.toString();
db_id = buff.substring(1, buff.indexOf("."));
db_device_id = buff.substring(buff.indexOf(".")+1, buff.indexOf(","));
db_install_date = buff.substring(buff.indexOf(",")+1, buff.length());
Date before = null;
try {
before = (Date)formatter.parse(db_install_date);
} catch (ParseException e) {
e.printStackTrace();
}
diff = now.getTime() - before.getTime();
runOnUiThread(new Runnable(){
@Override
public void run(){
UIAdd(diff,db_id,db_device_id,db_install_date);
}
});
} else { //IF buffer returns N
// TODO: Fill in
}
} while(buffer.charAt(0)=='Y');
UIFinish();
} catch(Exception err) {
err.printStackTrace();
}
}
@SuppressWarnings("deprecation")
public void UISetup()
{
tl.removeAllViews();
dbline();
TableRow titr = new TableRow(this);
titr.setLayoutParams(new LayoutParams( LayoutParams.FILL_PARENT,LayoutParams.WRAP_CONTENT));
TextView dbid0 = new TextView(this);
TextView dbdevid0 = new TextView(this);
TextView dbindate0 = new TextView(this);
dbid0.setText("| " + "_id");
dbdevid0.setText("| " + "device_id");
dbindate0.setText("| "+ "install_date"+" |");
titr.addView(dbid0);
titr.addView(dbdevid0);
titr.addView(dbindate0);
tl.addView(titr, new TableLayout.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT));
dbline();
}
@SuppressWarnings("deprecation")
public void UIAdd(long diffr, String dbidn,String did,String idate)
{
long days;
days = diffr / ONE_DAY;
TableRow tr = new TableRow(this);
tr.setLayoutParams(new LayoutParams( LayoutParams.FILL_PARENT,LayoutParams.WRAP_CONTENT));
TextView dbid = new TextView(this);
TextView dbdevid = new TextView(this);
TextView dbindate = new TextView(this);
dbid.setText("| " + dbidn);
dbdevid.setText("| " + did);
dbindate.setText("| " + idate+" |");
if(days <= 7)
{
activeinstalls++;
if(days <= 3)
{
dbid.setTextColor(Color.GREEN);
dbdevid.setTextColor(Color.GREEN);
dbindate.setTextColor(Color.GREEN);
} else {
dbid.setTextColor(Color.MAGENTA);
dbdevid.setTextColor(Color.MAGENTA);
dbindate.setTextColor(Color.MAGENTA);
}
} else {
dbid.setTextColor(Color.RED);
dbdevid.setTextColor(Color.RED);
dbindate.setTextColor(Color.RED);
}
tr.addView(dbid);
tr.addView(dbdevid);
tr.addView(dbindate);
tl.addView(tr, new TableLayout.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT));
}
public void UIFinish()
{
dbline();
TextView te = (TextView)findViewById(R.id.totalentries);
te.setText(String.valueOf(ID-1));
TextView au = (TextView)findViewById(R.id.activeusers);
au.setText(String.valueOf(activeinstalls));
}
@SuppressWarnings("deprecation")
public void dbline()
{
TableLayout tl=(TableLayout)findViewById(R.id.db_data);
TableRow tr = new TableRow(this);
tr.setLayoutParams(new LayoutParams( LayoutParams.FILL_PARENT,LayoutParams.WRAP_CONTENT));
TextView dbid = new TextView(this);
TextView dbdevid = new TextView(this);
TextView dbindate = new TextView(this);
dbid.setText("+---------");
dbdevid.setText("+-------------------------------");
dbindate.setText("+--------------------+");
tr.addView(dbid);
tr.addView(dbdevid);
tr.addView(dbindate);
tl.addView(tr, new TableLayout.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT));
}
}
最佳答案
移动这个
TableLayout tl=(TableLayout)findViewById(R.id.db_data);
到
onCreate()，因为在调用setContentView()之前必须先findViewById。