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);
}
}
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