android - 如何将自定义按钮添加到 Material 日期范围选择器android？

Question

如何向 Material 日期范围选择器添加自定义按钮？

我正在尝试获取对话框的 View ，以便可以以编程方式添加按钮，但我无法从选择器中获取任何 View 。

        MaterialDatePicker.Builder<Pair<Long,Long>> builder = MaterialDatePicker.Builder.dateRangePicker();
        MaterialDatePicker<Pair<Long,Long>> materialDatePicker = builder
            .setTitleText("Select Dates")
            .build();
        dateRangeTV.setOnClickListener(v -> {
            materialDatePicker.show(getSupportFragmentManager(), "DATE_PICKER");
            View root = materialDatePicker.requireView();
        });

但是我收到错误消息。

java.lang.IllegalStateException: Fragment MaterialDatePicker{e52ecfc} (40593b4f-a55a-4d6c-aa3b-2b778e721149 tag=DATE_PICKER) 未从 onCreateView() 返回 View ，或者在 onCreateView() 之前调用此 View 。

Answer 1

发生此错误的原因是 materialDatePicker.show() 是异步调用，并且 MaterialDatePicker (DialogFragment) 尚未创建，无法访问其 Root View 。为了避免此错误，您必须通过添加 DefaultLifecycleObserver 使用 materialDatePicker.getLifecycle() 监听 DialogFragment Lifecycle 并使用覆盖方法 void onStart(@NonNull LifecycleOwner Owner) 从那里访问 MaterialDatePicker Root View 。

将您的代码更改为如下所示:

MaterialDatePicker.Builder<Pair<Long,Long>> builder = MaterialDatePicker.Builder.dateRangePicker();
MaterialDatePicker<Pair<Long,Long>> materialDatePicker = builder
        .setTitleText("Select Dates")
        .build();
materialDatePicker.getLifecycle().addObserver(new DefaultLifecycleObserver()
{
    @Override
    public void onCreate(@NonNull LifecycleOwner owner) {}

    @Override
    public void onStart(@NonNull LifecycleOwner owner) {
        //in onStart of DialogFragment the View has been created so you can access the materialDatePicker.requireView()
        View root = materialDatePicker.requireView();
        //from root find the View you are interested to add your custom button
    }

    @Override
    public void onResume(@NonNull LifecycleOwner owner) {}

    @Override
    public void onDestroy(@NonNull LifecycleOwner owner) {
        //remove Lifecycle Observer
        materialDatePicker.getLifecycle().removeObserver(this);
    }
});
materialDatePicker.show(getSupportFragmentManager(), "DATE_PICKER");