Error creating relative layout using Java code
I am new to android development and was trying to create a RelativeLayout using Java code. Below is my MainActivty.java
package com.rt.droid.rellayoutjava;
import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.RelativeLayout.LayoutParams;
public class MainActivity extends Activity {
RelativeLayout r;
public static LayoutParams msgDim;
EditText userNameVal, passwordVal;
TextView message, userName, password;
Button login;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
init();
createMessage();
r.addView(message,msgDim);
setContentView(r);
}
public void init() {
r = new RelativeLayout(this);
LayoutParams dimensions = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
r.setLayoutParams(dimensions);
userNameVal = new EditText(this);
passwordVal = new EditText(this);
message=new TextView(this);
userName = new TextView(this);
password = new TextView(this);
login = new Button(this);
}
public void createMessage(){
LayoutParams msgDim = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
msgDim.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
message.setLayoutParams(msgDim);
message.setText("Please login first");
message.setTextColor(Color.rgb(0,0,0));
}
}
However I am getting a null pointer exception (below from Logcat)
Process: com.rt.droid.rellayoutjava, PID: 2471
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.rt.droid.rellayoutjava/com.rt.droid.rellayoutjava.MainActivity}: java.lang.NullPointerException: Attempt to read from field 'int android.view.ViewGroup$LayoutParams.width' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to read from field 'int android.view.ViewGroup$LayoutParams.width' on a null object reference
at android.view.ViewGroup$LayoutParams.<init>(ViewGroup.java:6403)
at android.view.ViewGroup$MarginLayoutParams.<init>(ViewGroup.java:6685)
at android.widget.RelativeLayout$LayoutParams.<init>(RelativeLayout.java:1345)
at android.widget.RelativeLayout.generateLayoutParams(RelativeLayout.java:1104)
at android.view.ViewGroup.addViewInner(ViewGroup.java:3889)
at android.view.ViewGroup.addView(ViewGroup.java:3733)
at android.view.ViewGroup.addView(ViewGroup.java:3709)
at com.rt.droid.rellayoutjava.MainActivity.onCreate(MainActivity.java:24)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Any pointers would be appreciated.
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2 answers
First of all, I suggest you use XML files to define your layout instead of programmatically programming them (you can search for any example and tutorial).
Anyway, your particular problem is with the msgDim variable not being initialized . Change onCreate () to this:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
init();
createMessage();
msgDim = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
r.addView(message,msgDim);
setContentView(r);
}
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Try using this:
r = new RelativeLayout(this);
RelativeLayout.LayoutParams dimensions = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.MATCH_PARENT,
RelativeLayout.LayoutParams.MATCH_PARENT);
r.setLayoutParams(dimensions);
The first answer on this question has more complete code: Programmatically Create a RelativeLayout in Android
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