Multiple SeekBar activity fatal crash-Collection of common programming errors
I have this MainActivity class in Android with multiple SeekBars:
package com.simplemathgame;
import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;
import android.widget.TextView;
public class MainActivity extends Activity implements OnSeekBarChangeListener {
private TextView numberOfAddDrills = (TextView) findViewById(R.id.add_drills_number);
private TextView numberOfSubDrills = (TextView) findViewById(R.id.sub_drills_number);
private TextView numberOfMulDrills = (TextView) findViewById(R.id.mul_drills_number);
private TextView numberOfDivDrills = (TextView) findViewById(R.id.div_drills_number);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SeekBar addSeekBar = (SeekBar) findViewById(R.id.add_seek_bar);
SeekBar subSeekBar = (SeekBar) findViewById(R.id.sub_seek_bar);
SeekBar mulSeekBar = (SeekBar) findViewById(R.id.mul_seek_bar);
SeekBar divSeekBar = (SeekBar) findViewById(R.id.div_seek_bar);
addSeekBar.setOnSeekBarChangeListener(this);
subSeekBar.setOnSeekBarChangeListener(this);
mulSeekBar.setOnSeekBarChangeListener(this);
divSeekBar.setOnSeekBarChangeListener(this);
Log.w("here","2");
}
@Override
public void onProgressChanged(SeekBar arg0, int arg1, boolean arg2){
Log.w("here","3");
switch (arg0.getId())
{
case R.id.add_seek_bar:
numberOfAddDrills.setText(""+arg1);
break;
case R.id.sub_seek_bar:
numberOfSubDrills.setText(""+arg1);
break;
case R.id.mul_seek_bar:
numberOfMulDrills.setText(""+arg1);
break;
case R.id.div_seek_bar:
numberOfDivDrills.setText(""+arg1);
break;
}
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
}
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
}
}
Here is the LogCat:
12-20 08:58:49.402: D/dalvikvm(668): GC_EXTERNAL_ALLOC freed 43K, 53% free 2546K/5379K, external 1917K/2137K, paused 43ms
12-20 08:58:52.563: D/AndroidRuntime(668): Shutting down VM
12-20 08:58:52.563: W/dalvikvm(668): threadid=1: thread exiting with uncaught exception (group=0x40015560)
12-20 08:58:52.582: E/AndroidRuntime(668): FATAL EXCEPTION: main
12-20 08:58:52.582: E/AndroidRuntime(668): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.simplemathgame/com.simplemathgame.MainActivity}: java.lang.NullPointerException
12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569)
12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
12-20 08:58:52.582: E/AndroidRuntime(668): at android.os.Handler.dispatchMessage(Handler.java:99)
12-20 08:58:52.582: E/AndroidRuntime(668): at android.os.Looper.loop(Looper.java:123)
12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.ActivityThread.main(ActivityThread.java:3683)
12-20 08:58:52.582: E/AndroidRuntime(668): at java.lang.reflect.Method.invokeNative(Native Method)
12-20 08:58:52.582: E/AndroidRuntime(668): at java.lang.reflect.Method.invoke(Method.java:507)
12-20 08:58:52.582: E/AndroidRuntime(668): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
12-20 08:58:52.582: E/AndroidRuntime(668): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
12-20 08:58:52.582: E/AndroidRuntime(668): at dalvik.system.NativeStart.main(Native Method)
12-20 08:58:52.582: E/AndroidRuntime(668): Caused by: java.lang.NullPointerException
12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.Activity.findViewById(Activity.java:1647)
12-20 08:58:52.582: E/AndroidRuntime(668): at com.simplemathgame.MainActivity.(MainActivity.java:11)
12-20 08:58:52.582: E/AndroidRuntime(668): at java.lang.Class.newInstanceImpl(Native Method)
12-20 08:58:52.582: E/AndroidRuntime(668): at java.lang.Class.newInstance(Class.java:1409)
12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561)
12-20 08:58:52.582: E/AndroidRuntime(668): ... 11 more
12-20 08:58:54.923: I/Process(668): Sending signal. PID: 668 SIG: 9
I don’t know where is this java.lang.RuntimeException. Thanks
-
You should take a look here, and see what’s null at that point:
12-20 08:58:52.582: E/AndroidRuntime(668): Caused by: java.lang.NullPointerException 12-20 08:58:52.582: E/AndroidRuntime(668): at android.app.Activity.findViewById(Activity.java:1647) 12-20 08:58:52.582: E/AndroidRuntime(668): at com.simplemathgame.MainActivity.(MainActivity.java:11)So line 11 is where the crash is.
The problem is you cannot call findViewById from there, call them inside the OnCreate method, after the setContentView.
Hope that helps.
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You have to include all the
findViewById()for TextView’s insideonCreate()because withoutsetContentView()it will returnnull.private TextView numberOfAddDrills; private TextView numberOfSubDrills; private TextView numberOfMulDrills; private TextView numberOfDivDrills; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); numberOfAddDrills = (TextView) findViewById(R.id.add_drills_number); numberOfSubDrills = (TextView) findViewById(R.id.sub_drills_number); numberOfMulDrills = (TextView) findViewById(R.id.mul_drills_number); numberOfDivDrills = (TextView) findViewById(R.id.div_drills_number); ..... }