I am new to Android Development, and I can't for the life of me, figure out why this is giving me an error. The error is occurring on this line: 'bu.setOnClickListener(new OnClickListener() {'
I am following the Android Development Fundamental tutorials on Lynda.com; and my code is identical to that of the teachers; or so I think.
package com.lynda.lyndaproject;
import android.os.Bundle;
import android.app.Activity;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
public class Main extends Activity {
Button bu = (Button) findViewById(R.id.button1);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bu.setOnClickListener(new OnClickListener() {
public void onClick(View v){
}
});
}
}
By the way, Eclipse doesn't seem to be allowing me to import anything; and I do believe importing 'android.view.View' should have imported everything necessary.
First, you need to fix your import. You are using the wrong OnClickListener. Change the line
import android.content.DialogInterface.OnClickListener;
to
import android.view.View.OnClickListener;
Next, You need to move the line
Button bu = (Button) findViewById(R.id.button1);
To after the call to setContentView(...). So your onCreate method would look like:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button bu = (Button) findViewById(R.id.button1);
bu.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v){
}
});
}
This is because findViewById(...) looks for a View in the current layout. Since this has not been set by setContentView, it will always return null.
Related
I recently use android studio instead of eclipse.
but somthing is wrong!
these are main java code that run currectly in eclipse but now get errors!
package com.example.amir.myapplicationeeee;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.view.View.OnClickListener;
public class MainActivity extends Activity {
Button button=(Button)findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
startActivity(new Intent(getApplicationContext(),Main2Activity.class));
finish();
}
});
setOnClickListener is hilighed red and error ";" excepted showed when want to runnin app in virtual device
If the code you provide here is exactly the same as you have in your project, then you should just add '}' on the end of your code - it closes the MainActivity class.
You should also have evertyhing implemented inside onCreate() method.
So it should look like:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button=(Button)findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
startActivity(new
Intent(this,Main2Activity.class));
finish();
}
});
}
}
I caught the error message
"5-14 12:39:13.104 2518-2518/com.example.fdai3744.neueleereapp E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.fdai3744.neueleereapp, PID: 2518 java.lang.RuntimeException: Unable to instantiate activity ..."
and here's my Java Code
package com.example.fdai3744.neueleereapp;
import android.net.wifi.p2p.WifiP2pManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
public Button button_1 = (Button) findViewById(R.id.button1); //Button
public TextView text1 = (TextView)findViewById(R.id.text1); // Textview
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button_1.setOnClickListener(new View.OnClickListener() { // Here I add the ActionListener for my button
#Override
public void onClick(View v) {
text1.setText("Button 1 wurde geklickt!");
}
});
}
}
If I start my App the emulator throws an error message "App has stopped". How should I prevent this error?
Well, your view hierarchy needs to be alive before your retrieve individual Views from it and the method setContentView() brings it to life(or instantiates it).
How?
setContentView(View) is a method exclusively available for Activity.
Internally it calls the setContentView(View) of Window. This method
sets the activity content to an explicit view. This view is placed
directly into the activity's view hierarchy. Calling this function
"locks in" various characteristics of the window that can not, from
this point forward, be changed. Hence it is called only once.
So, instead of initializing the Views as instance variables, instantiate them inside onCreate() after setContentView().
Also read: Android: setContentView and LayoutInflater
caused by
public Button button_1 = (Button) findViewById(R.id.button1); //Button
public TextView text1 = (TextView)findViewById(R.id.text1); // Textview
never assign view before setContentView() is called
your modified code
package com.example.fdai3744.neueleereapp;
import android.net.wifi.p2p.WifiP2pManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
public Button button_1;
public TextView text1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button_1 = (Button) findViewById(R.id.button1); //Button
text1 = (TextView)findViewById(R.id.text1); // Textview
button_1.setOnClickListener(new View.OnClickListener() { // Here I add the ActionListener for my button
#Override
public void onClick(View v) {
text1.setText("Button 1 wurde geklickt!");
}
});
}
}
I'm trying to implement onclicklistener but it isn't working on my phone or emulator.
here is the code:
package com.slaps.guess;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity implements OnClickListener {
TextView tv;
Button one;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
one = (Button) findViewById(R.id.button1);
tv = (TextView) findViewById(R.id.tvd);
}
public void onClick(View v) {
switch (v.getId()) {
case R.id.button1:
tv.setText("Anything");
break;
}
}
}
the text view is not changing to anything it is still.
note: button1 exists, and their is nothing wrong with my xml.
i want to implement because i have alot of button.
You are missing one.setOnClickListener(this) in your code.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
one = (Button) findViewById(R.id.button1);
one.setOnClickListener(this);
tv = (TextView) findViewById(R.id.tvd);
}
Before using listener you will have to add it in the object for which you want it.
I guess you want for the Button one here.
Use one.setOnClickListener(this) after one = (Button) findViewById(R.id.button1);
It looks like you're missing the required XML attribute in res/layout/activity_main.xml. Ensure it looks like:
<Button
android:id="#+id/button1"
onClick="onClick"
/>
The key being you have supplied the onClick attribute with the name of your method to invoke.
But if you want to set the click listener programmatically than you will need to use the Button.setOnClickListener method. If you do this your method signature will need to change to:
one.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Perform action on click
}
});
I used samples from similar code to make this, unfortunately I'm not to sure what I did wrong.
The purpose of this app is to output text entered in a field to a TextView, where I changed the color, when a button is pressed.
package edu.wmich.project3
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.view.View.OnClickListener;
public class Main extends Activity {
String txtResult;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button text =(Button) findViewById(R.id.btnColor0);
final TextView result = ((TextView) findViewById(R.id.txtResult));
text.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
txtResult= getText(R.id.txtField0).toString();
result.setText(txtResult);
}
});
}
}
txtResult = (findViewById(R.id.txtField0)).toString();
will solve...
the problem is that you're using the method getText() from the Activity which has nothing to do with the TextField you're dealing with.
...what is the type of view of R.id.txtField0? I guess with this you can take it from here.
This code to change text when the user presses a button doesn't work. i tried to change it in some ways but i can't figure out why won't it change... please give me a bit help
package com.cookbook.simple_activity;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class activity extends Activity {
private TextView txt = (TextView) findViewById(R.id.hello_text);
Button startButton = (Button) findViewById(R.id.trigger);
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
startButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
txt.setText(R.string.pressthisbutton);
}
});
}
}
Change it to
public class activity extends Activity {
private TextView txt;
Button startButton;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
txt = (TextView) findViewById(R.id.hello_text);
startButton = (Button) findViewById(R.id.trigger);
You need to initialize your Views after inflating your layout with setContentView(). Since your Views exist in your layout, they will return null if you haven't inflated your layout first. You can declare them before your setContentView() but you can't initialize them until after.
Also, since you are trying to access txt inside your listener it must either be final or declared as a member variable as above.
This was a rather easy one to spot but they aren't always. When you post a question try to describe what isn't working and how. Here it would be a NPE I'm guessing when you try to set the listener on your Button so it crashes. When it does crash, please provide the logcat so it is easier for us to spot the problem.
package com.cookbook.simple_activity;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class activity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
final TextView txt = (TextView) findViewById(R.id.hello_text);
Button startButton = (Button) findViewById(R.id.trigger);
startButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
txt.setText("your text");
}
});
}
}
try this, I moved your button and textview declaring to the body of the activity.
android life cycle always starts with onCreate() method assign the id inside the onCreate
don't use private modifer for the TextView
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class activity extends Activity {
TextView txt;
Button startButton;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
txt = (TextView) findViewById(R.id.hello_text);
startButton = (Button) findViewById(R.id.trigger);
startButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
txt.setText(R.string.pressthisbutton);
}
});
}
}
Always initialize your textview and other widgets in oncreate method other wise youll get NullPointerException
Try this way
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
txt = (TextView) findViewById(R.id.hello_text);
startButton = (Button) findViewById(R.id.trigger);
txt.setText("It Working Now!!");