Question

我有html

<input name="name" [(ngModel)]="address.name" matInput >

和我的ts一样

  public address: Address;

  ...

  ngOnInit() {
    this.service.getAddress(1).subscribe(address => {          
      this.address = address;
    });
  }

我的界面看起来像

export interface Address {
  ...
  name: string;
}

当我尝试填充输入时，出现错误：

TypeError：无法读取未定义的属性“名称”

我知道发生这种情况是因为address对象为null，直到在subscribe方法中填充它为止。如何摆脱这个错误？

Answer 1

按以下步骤初始化为空对象，

public address = new Address();

或在模板（脏）中使用* ngIf

<input name="name" *ngIf="address" [(ngModel)]="address.name" matInput >

是 export class Address {...}

Answer 2

如果要考虑这一点，请尝试使用public class MainActivity extends AppCompatActivity implements BottomNavigationView.OnNavigationItemSelectedListener { Fragment Frag = new Fragment(); Fragment FragmentA; Fragment FragmentB; Fragment FragmentC; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); BottomNavigationView navigation = findViewById(R.id.navigation); navigation.setOnNavigationItemSelectedListener(this); // mOnNavigationItemSelectedListener FragmentA = new FragmentA(); FragmentB = new FragmentB(); FragmentC = new FragmentC(); if (savedInstanceState != null) { Frag = getSupportFragmentManager().getFragment(savedInstanceState, "Frag"); } else loadFragment(FragmentA); } @Override public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) { Fragment fragment = null; int i = menuItem.getItemId(); if (i == R.id.fragmentA) { fragment = FragmentA; } else if (i == R.id.fragmentB) { fragment = FragmentB; } else if (i == R.id.fragmentC) { fragment = FragmentC; } return loadFragment(fragment); } private boolean loadFragment(Fragment fragment) { if (fragment != null) { getSupportFragmentManager().beginTransaction().hide(FragmentA).commit(); getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment).commit(); getSupportFragmentManager().beginTransaction().show(fragment).commit(); Frag = fragment; return true; } return false; } @Override protected void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); getSupportFragmentManager().putFragment(outState, "Frag", Frag); } }作为可选类型，然后将any分配给{}：

address

从服务器获取数据之前，“无法读取未定义的属性'名称'”

2 个答案: