The specified child already has a parent. You must call removeView() on the child's parent first

Question

I am doing a little exercise about a application you that put your name, and it returns "hello (the name you put)". But after i push the button i get the error "The specified child already has a parent. You must call removeView() on the child's parent first"

MainActivity.java

package com.example.holaamigos;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.*;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity {
    public final static String EXTRA_SALUDO = "com.example.holaamigos.SALUDO";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        final EditText txtNombre = (EditText)findViewById(R.id.TxtNombre);
        final Button btnHola = (Button)findViewById(R.id.BtnHola);
            
            btnHola.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(MainActivity.this, ActivitySaludo.class);
                    String saludo = txtNombre.getText().toString();
                    intent.putExtra(EXTRA_SALUDO, saludo);
                    startActivity(intent);
        }
                
    });
            
    }
                    
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

ActivitySaludo.java

package com.example.holaamigos;


import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;

public class ActivitySaludo extends Activity {
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_saludo);
        
        Intent intent = getIntent();
        String saludo = intent.getStringExtra(MainActivity.EXTRA_SALUDO);
        
        //TextView txt = new TextView(this);
        //txt.setText(20);
        //txt.setText(saludo);
        
        TextView txtCambiado = (TextView) findViewById(R.id.TxtSaludo);
        txtCambiado.setText(saludo);
        setContentView(txtCambiado);
    }

}

activity_saludo.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    
    <TextView 
        android:id="@+id/TxtSaludo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="" />
    

</LinearLayout>

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/LblNombre"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/nombre" />
    
    <EditText
        android:id="@+id/TxtNombre"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="text" />
    
    <Button 
        android:id="@+id/BtnHola"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hola_apy"
        android:onClick="enviarSaludo"/>

</LinearLayout>

LogCat

10-10 16:12:18.470: D/AndroidRuntime(810): Shutting down VM
10-10 16:12:18.470: W/dalvikvm(810): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
10-10 16:12:18.586: E/AndroidRuntime(810): FATAL EXCEPTION: main
10-10 16:12:18.586: E/AndroidRuntime(810): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.holaamigos/com.example.holaamigos.ActivitySaludo}: java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.os.Looper.loop(Looper.java:137)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.ActivityThread.main(ActivityThread.java:5041)
10-10 16:12:18.586: E/AndroidRuntime(810):  at java.lang.reflect.Method.invokeNative(Native Method)
10-10 16:12:18.586: E/AndroidRuntime(810):  at java.lang.reflect.Method.invoke(Method.java:511)
10-10 16:12:18.586: E/AndroidRuntime(810):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
10-10 16:12:18.586: E/AndroidRuntime(810):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
10-10 16:12:18.586: E/AndroidRuntime(810):  at dalvik.system.NativeStart.main(Native Method)
10-10 16:12:18.586: E/AndroidRuntime(810): Caused by: java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.view.ViewGroup.addViewInner(ViewGroup.java:3339)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.view.ViewGroup.addView(ViewGroup.java:3210)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.view.ViewGroup.addView(ViewGroup.java:3186)
10-10 16:12:18.586: E/AndroidRuntime(810):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:289)
10-10 16:12:18.586: E/AndroidRuntime(810):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:279)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.Activity.setContentView(Activity.java:1901)
10-10 16:12:18.586: E/AndroidRuntime(810):  at com.example.holaamigos.ActivitySaludo.onCreate(ActivitySaludo.java:25)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.Activity.performCreate(Activity.java:5104)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
10-10 16:12:18.586: E/AndroidRuntime(810):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
10-10 16:12:18.586: E/AndroidRuntime(810):  ... 11 more
10-10 16:12:18.856: D/dalvikvm(810): GC_CONCURRENT freed 134K, 10% free 2630K/2908K, paused 73ms+83ms, total 237ms

Answer 1

I encountered this error whenever I omitted a parameter while inflating the view for a fragment in the onCreateView() method like so:

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view=inflater.inflate(R.layout.fragment_reject, container);
    return view;
}

The solution is to change the view inflation line to:

View view=inflater.inflate(R.layout.fragment_reject, container,false);

The explanation can be found at the Android guide for fragments

Quoting from the guide, the final parameter in the view initialization statement is false because:

"the system is already inserting the inflated layout into the container—passing true would create a redundant view group in the final layout"

Answer 2

In onCreate with activity or onCreateView with fragment

 if (view != null) {
    ViewGroup parent = (ViewGroup) view.getParent();
    if (parent != null) {
        parent.removeView(view);
    }
}
try {
    view = inflater.inflate(R.layout.fragment_main, container, false);
} catch (InflateException e) {
    e.printStackTrace();
}

Answer 3

in ActivitySaludo, this line,

    setContentView(txtCambiado);

you must set the content view for the activity only once.

Answer 4

You dont need this line: setContentView(txtCambiado);