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visual studio android import cant resolved after update

I updated Visual Studio, then my Android project had errors such as import could not be resolved. It could not be resolved to a text type. The type could not be resolved. Then I created a new project with the same settings. However, it had the same errors. It does not work because of the code, but maybe it knows who knows the code here.
package com.Android2;
import android.app.Activity;
import android.widget.TextView;
import android.os.Bundle;
public class Android2 extends Activity
{
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
/* Create a TextView and set its text to "Hello world" */
TextView tv = new TextView(this);
tv.setText("Hello World!");
setContentView(tv);
}
}

There is no problem with your code or imports...
I know it is hard work and a serious change when it comes to shortcuts, menus, overview, etc., but i would suggest to use android studio instead of visual studio if you only write android apps in java. I used visual studio too and switched to android studio.
Android Studio will give you more comfort than every other ide in programming android apps in java!
I know this problems you wrote about very well and had the same. Sry that this isnt a really answer of your problem and does not solves your concrete problem.
Tips for solving, you probably already know:
reboot your pc and visual studio if you not already did
delete caches or other from visual studio
rebuilt/clean your project
not easy, but reinstall visual studio
I hope i could help anyway!

Is Androids new Jack compiler really that slow?

On some of my Android projects I see that building got quite slow since using the new Jack compiler. I need it to use Java 8 features like lambdas.
But the long building time is a bit disturbing. So I set up a new Android project. It contains just a MainActivity with one button which reacts on your click.
package de.xappo.myapplication;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
Button button;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(final View view) {
Toast.makeText(MainActivity.this, "Button clicked!", Toast.LENGTH_LONG).show();
}
});
}
}
There is nothing else except from the layout file which just contains a a TextView and a Button within a RelativeLayout.
As you can see in the picture all the jack gradle tasks together take about 75 seconds. Is this normal? This hole example app builds in less than 22 seconds without jack. So is this big difference normal?
I already managed Java heap size within my gradle.properties file:
org.gradle.jvmargs=-Xmx2048m -XX:MaxPermSize=512m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8
Is there still any thing to do to improve jack compiling performance? Or do you know about any updates planned on jack to improve building time?

As per this announcement, the Jack toolchain on Android is deprecated and java8 support will be directly integrated into Android's standard javac and dx toolchain. I switched to Jack for java8 support, but then transitioned to retrolambda because Jack was so slow.

Android activity & import issue

Trying out some android programming that has gone fine up until this point. I'm getting the following errors:
Activity cannot be resolved to a type
The import Activity cannot be resolved
on the top two imports (activity and bundle) of the following class:
package com.example.sqlite;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.EditText;
public class Input extends Activity {
private EditText txtTitle;
private EditText txtURL;
private Button btnOK;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.input);
txtTitle = (EditText) findViewById(R.id.editText1);
txtURL = (EditText) findViewById(R.id.editText2);
btnOK = (Button) findViewById(R.id.button1);
}
}
I've done the standard ctrl + shift + O, which does automatically add these imports but the errors remain. I've also rebuilt it over and over with no effect.
Ca anyone see were I'm going wrong here?

Do right click on the project node in Eclipse and select Android Tools->Fix Project Properties. It looks like you are missing link to your Android libraries. Good way to check on that is to open properties-> Java build path -> Libraries and verify that Android link is there. If not - do Properties->Android and select project target you would like to use

You may occasionally see strange erros if any of your XML files fail to build. Check your console to see if any of your layout or resources have errors. Do the following:
Project > Clean
If this does not fix it, verify that pour souce actually exists in the project path:
com.example.sqlite

Check your manifest xml if the activity is included.. This can sometimes cause the error.

OnClickListener Error

I am new to Android and tried to run the sample code of the SDK using eclipse. I created the project (via File → New → Project → Android → Android Sample Project), but when I run the project it shows the following error for all the sample projects:
Multiple markers at this line
The method onClick(View) of type new View.OnClickListener(){} must override a superclass method
implements android.view.View.OnClickListener.onClick
Then I refered to this forum. Here they mentioned a "compiler compliance level". But my compiler compliance level is on 1.7, and I am using Android 4.0.3 with an API level of 15.
So please help me to rectify this error.

Make sure that above your OnClick method you have the annotation #Override like so
#Override
public void OnClick(View v) {
//Code goes here
}
By having #Override, Java knows that you are not creating a new method, in this situation you are letting Java know that you are utilizing that listener.
If you have already done this, check this website http://androidcodemonkey.blogspot.com/2011/10/how-to-solve-must-override-superclass.html

Remove the #Override annotation tag.
For some situation. the eclipse can't recognize.

I just had the same issue.I fixed it by following change of code
Button button = (Button) findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
Use View.OnClickListener(){} instead of just OnClickListener(){};
I think this might due to various OnClickListener are there. May be we need to specify which is the relevant one. I would really love to know the real reason if any one knows.

Missing Something Easy (Button OnClick Causing Null Pointer)

Suddenly my buttons cause null pointer exceptions. I have not changed any code in this activity class. I have been up most of the weekend trying to pin this down. I get null pointer exceptions in both the emulator and on device.
This is a simple screen with buttons. I could easily scrap this and write new code, but would like to know what has caused this issue. If not, I will just write new code.
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
Button b1 = (Button) findViewById(R.id.MainActBtn);
b1.setOnClickListener(new View.OnClickListener() { //Error is here
public void onClick(View v) {
Intent intent = new Intent(StartScreen.this, MainActivity.class);
startActivity(intent);
}
});
Any help?

Try a fresh clean and build of your project. I got this error too in the past, caused by a changed R.class Resource class, but the static references in the using classes weren't properly replaced by the incremental java compiler, so the resources are no longer found.

I think You are not getting Null Pointer Exception because of the Button click just because of the declaration of the button..
You can check before writting the onClickListener..
if(b1==null)
Log.i("Null","Null");
The Problem is may be in setting the XML view or also check the button you are using is defined in the same xml you are using in setContentView.
After this all, also Clean and Build your project.