Question

我试图在片段隐藏之前设置过渡动画，但是我得到了nullpointerexception。没有.setCustomAnimation方法，代码可以正常运行并且片段被隐藏，空指针从何而来？

public class MainActivity extends AppCompatActivity {
    private TextView mavisTxt;
    private Button testBtn;
    private HeaderNav navigationBar;

    private FragmentManager fm;
    private FragmentTransaction ft;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initVariables();

    }

    private void initVariables() {
        fm = getSupportFragmentManager();
        ft = fm.beginTransaction();
        navigationBar = (HeaderNav)fm.findFragmentById(R.id.navigationBar);

        mavisTxt = (TextView)findViewById(R.id.mavisTxt);
        testBtn = (Button)findViewById(R.id.testBtn);


        testBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                    ft.setCustomAnimations(android.R.animator.fade_in, android.R.animator.fade_out);
                    ft.hide(navigationBar)
                    .commit();
                    if(navigationBar.isHidden()) {mavisTxt.setText("navbar is hidden");}
            }
        });

    }
}

这是我得到的日志：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.ViewGroup.startViewTransition(android.view.View)' on a null object reference

Answer 1

看一下这篇文章： Attempt to invoke virtual method 'android.view.View android.view.View.getRootView()' on a null object reference

然后查看是否有与此相关的内容以及这3行

navigationBar = (HeaderNav)fm.findFragmentById(R.id.navigationBar);
mavisTxt = (TextView)findViewById(R.id.mavisTxt);
testBtn = (Button)findViewById(R.id.testBtn);

片段事务空指针

1 个答案: