When user hits the BACK-Button on his android device, the keyboard disappears. How can I catch that event? In order to track softkeyboard is open or not, this tutorial is helpfull for you, and you will easily dissmiss the softkeyboard by pressing back button.

Create a class BackAwareEdittext that extends the EditText, just override the method onKeyPreIme to catch the KEYCODE_BACK event and ACTION_UP event.

private BackPressedListener mOnImeBack;

public BackAwareEdittext(Context context) {
    super(context);
}

public BackAwareEdittext(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public BackAwareEdittext(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
}

@Override
public boolean onKeyPreIme(int keyCode, KeyEvent event) {
    if(event.getKeyCode() == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_UP){
        if (mOnImeBack != null) mOnImeBack.onImeBack(this);
    }
    return super.dispatchKeyEvent(event);
}

public void setBackPressedListener(BackPressedListener listener) {
    mOnImeBack = listener;
}

public interface BackPressedListener {
    void onImeBack(BackAwareEdittext etWrite);
}

MainActivity.java

When user selects the EditText softkeyboard appear, and setBackPressedListener will dismisses the keyboard by pressing the BACK key.

 BackAwareEdittext etWrite=(BackAwareEdittext)findViewById(R.id.etWrite);

    etWrite.setBackPressedListener(new BackAwareEdittext.BackPressedListener() {
           @Override
           public void onImeBack(BackAwareEdittext etWrite) {
               isKeyboardOpen=false;
                   Toast.makeText(MainActivity.this,"Keyboard close",Toast.LENGTH_SHORT).show();
           }
       });

       etWrite.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               isKeyboardOpen=true;
               Toast.makeText(MainActivity.this,"Keyboard open",Toast.LENGTH_SHORT).show();
           }
       });

Make android:windowSoftInputMode="stateHidden" in **AndroidManifest.xml** to make sure that keyboard is closed(by default).