Question

我目前开始使用数据绑定库，在我的viewmodel中我有一个扩展的LiveData对象：

public class ScannerViewModel extends AndroidViewModel {

    /** MutableLiveData containing the scanner state to notify MainActivity. */
    public ScannerLiveData scannerLiveData;

ScannerLiveData：

public class ScannerLiveData extends MutableLiveData<ScannerLiveData> {
    public boolean mScanningStarted;
    public boolean mBluetoothEnabled;
    public boolean mLocationEnabled;

    public ScannerLiveData(final boolean bluetoothEnabled, final boolean locationEnabled) {
        mScanningStarted = false;
        mBluetoothEnabled = bluetoothEnabled;
        mLocationEnabled = locationEnabled;
        postValue(this);
    }
    ...
}

activity_scanner.xml：

<layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout_test">

    <data>
        <import type="android.view.View" />

        <variable
            name="livedata"
            type="de.datacollect.ecount.ui.scanner.ScannerLiveData" />
    </data>

    ...
    <android.support.constraint.ConstraintLayout
        <ProgressBar
            android:id="@+id/state_scanning"
            style="?android:attr/progressBarStyleHorizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="-7dp"
            android:layout_marginTop="-8dp"
            android:indeterminate="true"
            android:indeterminateTint="@android:color/white"
            android:visibility="@{livedata.mBluetoothEnabled ? View.VISIBLE : View.INVISIBLE}"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/recycler_view_ble_devices" />
        ...

ScannerActivity：

@Override
protected void onCreate(@Nullable final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ActivityScannerBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_scanner);

    // Create view model containing utility methods for scanning
    mScannerViewModel = ViewModelProviders.of(this).get(ScannerViewModel.class);
    mScannerViewModel.getScannerState().observe(this, this::startScan);

    binding.setLifecycleOwner(this);
    binding.setLivedata(mScannerViewModel.scannerLiveData);
    ...

如何绑定mBluetoothEnabled属性？我在构建时遇到了一个未分类的错误。我已经使用了搜索，但没有找到它的相关信息。每一个帮助都会受到赞赏。

顺便说一下：

数据绑定的更新：

现在，您可以将LiveData对象用作数据绑定表达式中的可观察字段。 ViewDataBinding类现在包含一个新的setLifecycle方法，您需要将其用于观察LiveData对象。

Answer 1

不是绑定LiveData对象，而是绑定您的视图模型。因此，将activity_scanner.xml中的 livedata 变量更改为

<variable
     name="viewModel"
     type="de.datacollect.ecount.ui.scanner.ScannerViewModel" />

和在ScannerActivity中

binding.setViewModel(mScannerViewModel);

然后您的绑定表达式将变为

android:visibility="@{viewModel.scannerLiveData.mBluetoothEnabled ? View.VISIBLE : View.INVISIBLE}"

Android - 对LiveData扩展对象的属性进行数据绑定

1 个答案: