I am new to android world and just started with some examples to gain understanding. In this example I am trying to display image from url but when i start the emulator and click on app icon it force closes.
the java file is:-
import java.io.InputStream;
import java.net.URL;
import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.widget.ImageView;
public class Lab1Activity extends Activity{
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ImageView imgView =(ImageView)findViewById(R.id.ImageView01);
Drawable drawable = LoadImageFromWebOperations("http://www.androidpeople.com/wp-content/uploads/2010/03/android.png");
imgView.setImageDrawable(drawable);
}
private Drawable LoadImageFromWebOperations(String url)
{
try
{
InputStream is = (InputStream) new URL(url).getContent();
Drawable d = Drawable.createFromStream(is, "src name");
return d;
}catch (Exception e) {
System.out.println("Exc="+e);
return null;
}
}
}
android manifest:-
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="cmpe235.lab1"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<application android:icon="#drawable/icon" android:label="#string/app_name">
<activity android:name=".Lab1Activity"
android:label="#string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
main.xml :-
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:id="#+id/LinearLayout01"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android">
<ImageView android:id="#+id/ImageView01"
android:layout_height="wrap_content" android:layout_width="wrap_content"/>
</LinearLayout>
at console DDMS i get this error:-
[2011-10-23 12:13:51 - ddms]null
java.lang.NullPointerException
at com.android.ddmlib.JdwpPacket.writeAndConsume(JdwpPacket.java:213)
at com.android.ddmlib.Client.sendAndConsume(Client.java:574)
at com.android.ddmlib.HandleHello.sendHELO(HandleHello.java:142)
at com.android.ddmlib.HandleHello.sendHelloCommands(HandleHello.java:65)
at com.android.ddmlib.Client.getJdwpPacket(Client.java:671)
at com.android.ddmlib.MonitorThread.processClientActivity(MonitorThread.java:317)
at com.android.ddmlib.MonitorThread.run(MonitorThread.java:263)
So how to handle this nullpointer access? Thanks
I would not download the image when the app starts, proberly that causes the exception:
Drawable drawable = LoadImageFromWebOperations("http://www.androidpeople.com/wp-content/uploads/2010/03/android.png");
imgView.setImageDrawable(drawable);
Save the image to your 3 res/drawable folders and load it like this, if you want it as a background:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:id="#+id/LinearLayout01"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#drawable/youresavedfile"
</LinearLayout>
Both of the possible locations for NullPointerException I can see are in the line where you set the drawable into the image. They might be either because your image view is null, or because the drawable is null. I suggest you to check if the image view is null before operating it, and check if an exception was thrown in your downloading method.
Related
I am new to android development and learning listview from WSCube. I have seen several other youtube videos also but cannot find the solution to it. Please check and advise.
I have attached all the codes than i have worked on my system through watching from the videos of WsCube youtube channel.
enter image description here
Android Manifest
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<application
android:allowBackup="true"
android:dataExtractionRules="#xml/data_extraction_rules"
android:fullBackupContent="#xml/backup_rules"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/Theme.ListView"
tools:targetApi="31">
<activity
android:name=".MainActivity"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MAIN"></action>
<category android:name="android.intent.category.LAUNCHER"></category>
</intent-filter>
</activity>
</application>
</manifest>
Activity_Main
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<ListView
android:id="#+id/listView"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
Main Activity
package com.example.listview;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
ListView listView;
ArrayList<String> arrNames = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView.findViewById(R.id.listView);
arrNames.add("Daniel01");
arrNames.add("Daniel02");
arrNames.add("Daniel03");
arrNames.add("Daniel04");
arrNames.add("Daniel05");
arrNames.add("Daniel06");
arrNames.add("Daniel07");
arrNames.add("Daniel08");
arrNames.add("Daniel09");
arrNames.add("Daniel10");
arrNames.add("Daniel11");
arrNames.add("Daniel12");
arrNames.add("Daniel13");
arrNames.add("Daniel14");
arrNames.add("Daniel15");
arrNames.add("Daniel16");
arrNames.add("Daniel17");
arrNames.add("Daniel18");
arrNames.add("Daniel19");
arrNames.add("Daniel20");
ArrayAdapter<String> adapter = new ArrayAdapter<>(getApplicationContext(), android.R.layout.simple_list_item_1, arrNames);
listView.setAdapter(adapter);
}
}
You made a mistake here.
listView.findViewById(R.id.listView);
That is wrong. Because you use a dot . between listView and findViewById(R.id.listView);.
You need to initialize the listView variable. You can do that with equal to = See the example I gave here.
Solution
listView = findViewById(R.id.listView);
Whenever i try to make any app even simple hello world app every time i get this type of error, even in android virtual devices and android phone also, so i want to know that what are mistakes that i made every time in made, and can any one please make this code correct. So that i can run this app on my mobile phone.
this is my MainActivity_hello.java file
package com.example.helloapp1;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity_hello extends Activity {
TextView tb;
Button b;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_activity_hello);
addListenerOnButton();
tb= (TextView) findViewById(R.id.Tbox);
}
private void addListenerOnButton() {
// TODO Auto-generated method stub
b = (Button)findViewById(R.id.button1);
b.setOnClickListener(new OnClickListener()
{
public void onClick(View arg0)
{
tb.setText( String.format( " Hi ") );
}
});
}
#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_activity_hello, menu);
return true;
}
}
activity_main_activity_hello.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/button1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity_hello" >
<TextView
android:id="#+id/Tbox"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world" />
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/Tbox"
android:layout_centerHorizontal="true"
android:layout_marginTop="44dp"
android:text="Hit Me" />
</RelativeLayout>
Androidmanifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.helloapp1"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.helloapp1.MainActivity_hello"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
There could be many reasons, You have to be sure that:
The R. import is not R.android, which references to the Android System Resources. If it is, Your Button b is referred to the system framework button. This System Framework Button is identified with "button1".
Well, in Your case, I think You have the wright import, because You have no problem by using the id for the textView.
You gave Your RelativeLayout the same Id like the button:
android:id="#+id/button1"
The best way would be, give both another, different id.
I don´t know why You are using String.format(), just use tb.setText("Hi");
You are declaring the same id button1 twice, once in the layout and once for the button.
Change it to something else for your layout, like:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/holder1"
...
>
Since it seems like you are getting started with Android development I would recommend switching over to using Android Studio.
I'm trying to second an array of 1000000 ints from one Activity to another. It works fine with smaller numbers, but when I try 1000000, startActivity does nothing, and causes this to show in logcat:
E/JavaBinder(2239): !!! FAILED BINDER TRANSACTION !!!
Why?
Here's some code demonstrating the issue:
MainActivity.java
package com.example.a;
import android.os.Bundle;
import android.view.View;
import android.app.Activity;
import android.content.Intent;
public class MainActivity extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void startSecond(View v) {
startActivity(new Intent(this, SecondActivity.class).putExtra(
"a", new int[1000000]));
}
}
SecondActivity.java
package com.example.a;
import android.os.Bundle;
import android.app.Activity;
public class SecondActivity extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
}
}
activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="56dp"
android:layout_marginTop="31dp"
android:onClick="startSecond"
android:text="click clack" />
</RelativeLayout>
activity_second.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" >
</LinearLayout>
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.a"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.a.MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name="com.example.a.SecondActivity"></activity>
</application>
</manifest>
Why?
Because you are limited to 1MB per Binder transaction, and Binder underlies the Intent system. The size of your Intent, including all extras, needs to be under 1MB.
Okay, this is really ticking me off. I ran it on both my emulator and on an android device. The code does NOT display "Helloworld, Android -mykong.com". I start the app, find it on the emulator, click on it, and it goes to interface of the app. However, it is just a blank screen! This error is not an issue of me finding the app, its not with the emulator or the android phone, the issue has to lie either in the code or in the way the code is structured/built. I know the the helloworld code is 100% correct because its from a reputable tutorial site. These are my three pairs of code. Please help, I am in desperate need!
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.test123"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.test123.MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
MainActivity.java
package com.example.test123;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void activity()
{
Intent helloWorld = new Intent(getApplicationContext(), HelloWorldjavaactivity.class );
startActivity( helloWorld );
}
#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;
}
}
HelloWorldjavaactivity.java
package com.example.test123;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class HelloWorldjavaactivity extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView text = new TextView(this);
text.setText("Hello World, Android - mkyong.com");
setContentView(text);
}
}
Activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="35dp"
android:layout_marginTop="57dp"
android:text=""
/>
</RelativeLayout>
You're not starting the HelloWorldjavaactivity.java activity. You need something like the following in your MainActivity:
Intent helloWorld = new Intent(getApplicationContext(), HelloWorldjavaactivity.class );
startActivity( helloWorld );
Of course, you need that code to be triggered by some even, a button press for example.
It would be easier to just eliminate the second activity (since your MainActivity isn't doing anything anyway) and put the code in your MainActivity instead. You'll also need to edit the layout for your MainActivity so that it includes the appropriate views.
I tried to run first example from "Beginning Android Games" book (by Mario Zechner, Apress.com):
I copied this code to my project (MainActivity.java file):
HelloWorldActivity.java
package com.helloworld;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity implements View.OnClickListener {
Button button;
int touchCount;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
button = new Button(this);
button.setText( "Touch me!" );
button.setOnClickListener(this);
setContentView(button);
}
public void onClick(View v) {
touchCount++;
button.setText("Touched me " + touchCount + " time(s)");
}
}
but when I have run this simple application, I didn't see any button on the emulator (I have seen only an "Android" label. I tried "project-->clean..": no result. (and "project-->Build Automatically is swiched on). Where do I need to declare and describe this button? But I followed all steps described in the book. And at the end, I removed xml-file from layout folder at all.
Thanks.
________________Edited: Added xml-files___________
res-->layout-->activity_main.xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
</RelativeLayout>
AndroidManifest.xml:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.firstbuttontest2"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="4"
android:targetSdkVersion="11" />
<application
android:allowBackup="true"
android:debuggable="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.firstbuttontest2.MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
Try this it might help you.
Add button to particular layout. Like this
LinearLayout linearLayout=(LinearLayout)findViewById(R.id.linearLayout);
linearLayout.addView(button);
I know that there is a addContentView method which may be more what you are looking for as opposed to setContentView.
Try
setContentView(R.layout.activity_main)
then
button = (Button) findviewbyid(R.id.Button1);
this may solve your problem