How Do I Start Another Activity When A Button Defined In Main.xml Is Clicked

I have two classes. One is Main and the other is HelloWorld. When I click a button which is defined in main.xml I want it to display a message defined in HelloWorld class to start.

Solution 1:

Your second activity HelloWorld doesn't have set a content view so it doesn't find the Button and you throw a NullPointerException. You have to set a contentView with setContentView containing the Button with the id R.id.button1 like you did in the MainActivity.

Your HelloWorld activity:

publicclassHelloWorld<AlertDialogActivity> extendsActivity{

             protectedvoidonCreate(Bundle icicle) {
             super.onCreate(icicle);
             setContentView(R.layout.layout_hello);

             finalButtonbutton= (Button) findViewById(R.id.button1);
             button.setOnClickListener(newView.OnClickListener() {
                 publicvoidonClick(View view) {
      Toast.makeText(getApplicationContext(), "You clicked on OK", Toast.LENGTH_SHORT).show();
                 }
             });
    }
}

Where R.layout.layout_hello represents a xml file in the res/layout folder (named layout_hello.xml):

<?xml version="1.0" encoding="utf-8"?><LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="fill_parent"android:layout_height="fill_parent" ><Buttonandroid:id="@+id/button1"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Button1" /></LinearLayout>

It's the same thing like you did in the MainActivity.

Solution 2:

simple way

inlude android:onClick="onClickMyButton" as a attribute of Button in main.xml

remove onClickListener from this Button

now define this mathod in your Main Activity

publicvoidonClickMyButton(View view){

Intent intent = newIntent(Main.this, HelloWorld.class);
        startActivity(intent);


}

now start your application it should work fine

Solution 3:

Why did you comment that line? //setContentView(R.layout.content_layout_id);

The activity is looking for the button R.id.button1 is a null view.

Solution 4:

ya you must need to use setContentView()

un comment that code and try again