用于从onClickListener类显示Toast的上下文

Question

I have a MainActivity that handles the UIs and buttons, but I have a separate class that handles the onClickListener portion of the code. My Main class is defined as: public class MainActivity extends Activity and my buttons in the class are defined like:

MyButtonListener l = new MyButtonListener();
b1 = (Button) findViewById(R.id.button1);
b1.setOnClickListener(l);

The MyButtonListener class is defined as public class MyButtonListener extends MainActivity implements View.OnClickListener . The problem comes in, is when I try to make a toast in MyButtonListener . I do not know what context to put for the toast. I have tried: MainActivity.this, MyButtonListener.this, getContextApplication(). None of them seemed to work. This is how I am trying to show my toast:

Toast.makeText(MyButtonListener.this, message, Toast.LENGTH_LONG).show();

Does anyone what context to put in order to show the toast from the MyButtonListener class?

Answer 1

Create Global variable

Context context;

in MainActivity and set

context = this;

in onCreate Method of main activity

now pass the context in MyButtonListener Constructor like this

MyButtonListener l = new MyButtonListener(context);
    b1 = (Button) findViewById(R.id.button1);
    b1.setOnClickListener(l);

and in MyButtonListener add constructor

private Context context;

public MyButtonListener(Context context) {
    this.context = context;
}

and use that context in toast

Answer 2

add a Context to your MyButtonListener 's constructor and use it to show the Toast .

  public MyButtonListener(Context c);

from MainActivity :

 MyButtonListener l = new MyButtonListener(this);

Answer 3

Use View.getContext() from the parameters.

Eg:

...
void onClick(View v){
    Context ctx = v.getContext();
}
...

This saves you from passing a context manually.

Answer 4

It is not the context you are getting but a different context of a different reference, instead you can pass the reference of the main activity to your constructor of the MyButtonListener and use the context that was passed on it.

What you are doing is actually inheriting the mainactivity but not its reference by the time it is created so using the MyButtonListene.this wont bring the toast on front . so extending mainactivity is completely useless/pointless.

Answer 5

I do not see any reason to have MyButtonListener extend MainActivity.

Do something like this:

public class MyButtonListener implements View.OnClickListener {

    private Context context;

    public MyButtonListener(Context context) {
        this.context = context;
    }

    ...

}

And pass the context from MainActivity:

MyButtonListener l = new MyButtonListener(this.getApplicationContext());

Answer 6

MyButtonListener l = new MyButtonListener(getApplicationContext());
and create parameterize constructor  in 
MyButtonListener

and use that Context