如果您按下返回按钮，则会返回活动状态，但是您已经将按钮的可见性设置为“消失”，这就是为什么您看不到这些按钮的原因。您必须处理后退按钮，并将按钮的可见性再次设置为“可见”。
public class MainActivity extends AppCompatActivity { Button btn, btn1, btn2; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); btn = findViewById(R.id.btn); btn1 = findViewById(R.id.btn1); btn2 = findViewById(R.id.btn2); btn.setonClickListener(new View.onClickListener() { @Override public void onClick(View v) { btn.setVisibility(GONE); btn1.setVisibility(GONE); btn2.setVisibility(GONE); FragmentManager fm = getSupportFragmentManager(); TestFragment fragment = new TestFragment(); fm.beginTransaction().add(R.id.fragment_container, fragment).addToBackStack(null).commit(); } }); } //Handle your Back Button with onKeyDown method. @Override public boolean onKeyDown(int keyCode, KeyEvent event) { //Check for if Back Button is pressed. If pressed do below: if (keyCode == KeyEvent.KEYCODE_BACK) { onBackPressed(); //Return your activity back. btn.setVisibility(View.VISIBLE); //Set your btn's visibility as Visible. btn1.setVisibility(View.VISIBLE); //Set your btn1's visibility as Visible. btn2.setVisibility(View.VISIBLE); //Set your btn2's visibility as Visible. return true; } return super.onKeyDown(keyCode, event); }}
