返回监听加双击退出

   @Override
    public void onBackPressed() {
        //super.onBackPressed();
        L.d("返回");
        View inflate = View.inflate(Dingdanshenhe.this, R.layout.tssm, null);
        final AlertDialog alertDialog = new AlertDialog.Builder(Dingdanshenhe.this).setView(inflate).show();
        TextView tv_msg = inflate.findViewById(R.id.tv_msg);
        tv_msg.setText("是否返回");
        inflate.findViewById(R.id.cancel).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                alertDialog.dismiss();
            }
        });
        inflate.findViewById(R.id.ok).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                alertDialog.dismiss();
                finish();
            }
        });
    }

双击退出

// 双击退出
long backTime;
@Override
public void onBackPressed() {

    if (System.currentTimeMillis() - backTime > 2000){
        Toast.makeText(MainActivity.this,"再按一次退出",Toast.LENGTH_SHORT).show();
        backTime = System.currentTimeMillis();
        return;
    }
    super.onBackPressed();
}