Question

我在布局中有一个TextView：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/drawer_header"
  android:layout_width="match_parent"
  android:layout_height="@dimen/header_height"
  android:background="@drawable/avena_nav_drawer"
  android:gravity="bottom"
  android:orientation="vertical"
  android:padding="@dimen/header_left_padding"
  style="@style/AppTheme">

<!-- Correo de la cuenta -->
<TextView
  android:id="@+id/drawer_email"
  style="@style/Widget.AppCompat.Spinner"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:text="@string/user_email"
  android:textSize="14sp"
  android:textColor="@color/chalk"
  android:textAppearance="@style/TextAppearance.AppCompat.Body1" />

</LinearLayout>

现在，这样的布局充当了我的drawerlayout中的标题，如下所示：

<android.support.design.widget.NavigationView
    android:id="@+id/main_drawer"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    app:itemTextColor="@color/chalk"
    android:fitsSystemWindows="true"
    app:headerLayout="@layout/drawer_header"
    app:menu="@menu/action_menu" />

我一直在尝试从Activity中引用我的TextView，它扩展了包含NavigationView的布局（也尝试了另一种棘手/失败的方式），但它总是抛出一个空对象引用。

有人可以帮助我吗？

修改

这是logcat：

    01-07 22:59:00.149 4284-4284/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.avena.avena, PID: 4284
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.avena.avena/com.avena.avena.dashboard.Dashboard}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
    at android.app.ActivityThread.access$800(ActivityThread.java:151)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:135)
    at android.app.ActivityThread.main(ActivityThread.java:5254)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.avena.avena.dashboard.Dashboard.onCreate(Dashboard.java:70)
    at android.app.Activity.performCreate(Activity.java:5990)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
    at android.app.ActivityThread.access$800(ActivityThread.java:151) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:135) 
    at android.app.ActivityThread.main(ActivityThread.java:5254) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:372) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

以下是活动代码：

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    ...

    // Set and reference textview inside drawer
    TextView drawer_email = (TextView) findViewById(R.id.drawer_email);

    if (logged) {
        drawer_email.setText(email);
    } else {
        drawer_email.setText("Invitado");
    }

    // Set layout
    setContentView(R.layout.activity_main);

编辑2

在这里找到正确的答案：

Control view from inside navigation view

Answer 1

您没有夸大您的布局，您应该添加：

using (var cmd = new SqlCommand("select group1 from product where productname = @pn)", con))
{
    cmd.Parameters.Add(new SqlParameter("@pn", TextBox1.Text));

    reader = cmd.ExecuteReader();//got error

    while (reader.Read())
    {
        data = Convert.ToInt32(reader);//got error
    }    
}

后：

setContentView(R.layout.yourLayoutNameHere);

Answer 2

 @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        View view = LayoutInflater.from(context).inflate(R.layout... //whatever your inflating code is
        ...

        // Set and reference textview inside drawer
//here use view to access your item
        TextView drawer_email = (TextView) view.findViewById(R.id.drawer_email);

        if (logged) {
            drawer_email.setText(email);
        } else {
            drawer_email.setText("Invitado");
        }

如果没有设置布局或没有引用视图，则无法访问布局的任何项目。

因此，您需要先设置视图，然后访问textview

Answer 3

查看当前的代码，似乎是在扩充布局之前尝试访问TextView。

尝试以下方法：

// Set layout
setContentView(R.layout.activity_main);

调用setContentView后，此API会从布局资源中设置活动内容。资源将被夸大，将所有顶级视图添加到活动中。

在您访问TextView之前调用此方法。

TextView drawer_email = (TextView) view.findViewById(R.id.drawer_email);

Answer 4

首先你必须打电话

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

然后：

TextView drawer_email = (TextView) findViewById(R.id.drawer_email);
//and your rest of code..

如何引用drawerlayout中包含的布局内的元素

4 个答案: