Question

我正在尝试保存碎片数据。因此，当我更改手机和互联网的方向时，片段中的数据并没有消失

public class MainActivity extends AppCompatActivity {

public static final String KEY_TITLE = "title";
public static final String KEY_FRAGMENT = "fragment";

private String title= null;

Fragment fragment = new MovieFragment() ;

private BottomNavigationView.OnNavigationItemSelectedListener onNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
        switch (menuItem.getItemId()){
            case R.id.nav_movie:
                 fragment = new MovieFragment();
                 title = getString(R.string.movie);
                 getSupportActionBar().setTitle(title);
                 break;
            case R.id.nav_tv:
                fragment = new TvFragment();
                title = getString(R.string.tv);
                getSupportActionBar().setTitle(title);
                break;
        }
        return setFragment(fragment);
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    setFragment(new MovieFragment());
    title = getString(R.string.movie);
    getSupportActionBar().setTitle(title);

    BottomNavigationView bottomNavigationView = findViewById(R.id.bottomNavigation);
    bottomNavigationView.setOnNavigationItemSelectedListener(onNavigationItemSelectedListener);

    if (savedInstanceState == null){
        getSupportFragmentManager().beginTransaction().replace(R.id.frameLayout,fragment).commit();
        getSupportActionBar().setTitle(title);
    }else {
        fragment = getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT);
        title = savedInstanceState.getString(KEY_TITLE);

        getSupportFragmentManager().beginTransaction().replace(R.id.frameLayout, fragment).commit();
        getSupportActionBar().setTitle(title);
    }

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_language,menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
    if (item.getItemId() == R.id.change_language){
        Intent intent = new Intent(Settings.ACTION_LOCALE_SETTINGS);
        startActivity(intent);
    }
    return super.onOptionsItemSelected(item);
}

public boolean setFragment(Fragment fragment){
    if (fragment != null){
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.frameLayout,fragment)
                .commit();
        return true;
    }

    return false;
}

@Override
public void onSaveInstanceState(@NonNull Bundle outState, @NonNull PersistableBundle outPersistentState) {
    outState.putString(KEY_TITLE, title);
    getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT,fragment);
    super.onSaveInstanceState(outState, outPersistentState);

}

当我尝试旋转手机时，应用程序被强制关闭，并且在logcat中显示：

由于：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'java.lang.Class java.lang.Object.getClass（）' 在androidx.fragment.app.BackStackRecord.doAddOp（BackStackRecord.java:396）在androidx.fragment.app.BackStackRecord.replace（BackStackRecord.java:444）在androidx.fragment.app.BackStackRecord.replace（BackStackRecord.java:434）在com.example.submission3.MainActivity.onCreate（MainActivity.java:65）在android.app.Activity.performCreate（Activity.java:7224）在android.app.Activity.performCreate（Activity.java:7213）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1272）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2926）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3081）在android.app.ActivityThread.handleRelaunchActivityInner（ActivityThread.java:4847）

我尝试了很多方法，但是找不到解决方案。谢谢您的帮助！

空对象引用上的“ java.lang.Class java.lang.Object.getClass（）”以保存数据

0 个答案: