在AutoCompleteTextView上使用Android:text属性，如下所示

<com.google.android.material.textfield.TextInputLayout
                  
                    style="@style/Widget.MaterialComponents.TextInputLayout.FilledBox.ExposedDropdownMenu"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                
                    app:hintTextColor="@color/primary_color_3">

                    <AutoCompleteTextView
                        android:id="@+id/accType_dropdown"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:text="Select Something"
                        android:backgroundTint="@android:color/transparent"
                        android:inputType="none"
                        android:lineSpacingExtra="5sp"
                        android:textColor="@color/name_primary_color"
                        android:textSize="14sp" />

                </com.google.android.material.textfield.TextInputLayout>

AutoCompleteTextView可以与适配器一起工作。

只是举个例子:

    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/til"

创建适配器:

    ArrayList<String> items = new ArrayList<>();
    items.add("Material");
    items.add("Design");
    items.add("Components");

    ArrayAdapter<String> adapter = new ArrayAdapter<>(this,R.layout.item, items);
    TextInputLayout textInputLayout = findViewById(R.id.til);

设置默认值和适配器:

    ((MaterialAutoCompleteTextView) textInputLayout.getEditText()).setText(items.get(1));
    ((MaterialAutoCompleteTextView) textInputLayout.getEditText()).setAdapter(adapter);