TextView:
<TextView
android:id="@+id/ProfilName"
android:layout_width="148dp"
android:layout_height="77dp"
android:layout_marginStart="131dp"
android:layout_marginLeft="131dp"
android:layout_marginTop="225dp"
android:layout_marginEnd="132dp"
android:layout_marginRight="132dp"
android:layout_marginBottom="381dp"
android:gravity="center_horizontal"
android:text="TextView"
android:textAlignment="center"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
ImageView:
<ImageView
android:id="@+id/ProfilPicture"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="141dp"
android:layout_marginLeft="141dp"
android:layout_marginTop="84dp"
android:layout_marginEnd="142dp"
android:layout_marginRight="142dp"
android:layout_marginBottom="471dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:srcCompat="@tools:sample/avatars" />
声明:
private TextView mNameUser;
private ImageView mProfilPicture;
正在尝试获取其ID:
mNameUser = findViewById(R.id.ProfilName);
mProfilPicture = findViewById(R.id.ProfilPicture);
例如,编辑TextView的文本:
mNameUser.setText("");
结果:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
例如,我正在尝试从一个活动中更改位于另一个活动中的用户名。
由于您的LoginActivity在MainActivity之前,因此尚未创建MainActivity,因此您不能向其发送任何数据,也不能在其中找到任何视图,因为它的布局没有膨胀。
// 1. When user click on login button in your LoginActivity
Intent intent = new Intent(this, MainActivity.class); // this or LoginActivity.this
intent.putExtra("fofo", value); // value comes from EditText in your LoginActivity
startActivity(intent);
// 2. In onCreate() method in your MainActivity
Bundle extras = getIntent().getExtras();
if (extras != null) {
String value = extras.getString("fofo");
}
mNameUser.setText(value); // this line will edit your TextView in MainActivity