描述
我想要构建一个任务列表的应用程序。我希望使用RoomDatabse来存储信息。 我已经使用Room构建了数据库，并获取了信息然后保存到数据库中。 但是当我点击添加按钮时，出现了异常。 我已经在网上搜索了适当的解决方法，但没有找到有用的内容。 请帮助我。
我的异常信息
Caused by: java.lang.ClassNotFoundException: Didn't find class
"androidx.core.app.ActivityManagerCompat" while store data using Room.
My Android Studio Configuration
compileSdkVersion 27
buildToolsVersion '28.0.3'
minSdkVersion 15
targetSdkVersion 27
My Database Class
@Database(entities = {TaskEntry.class},version = 1,exportSchema = false)
@TypeConverters(DateConverter.class) 抽象类 AppDatabase 继承自 RoomDatabase。
该注解 @TypeConverters(DateConverter.class) 表示使用 DateConverter 类进行类型转换。
private static final String LOG_TAG=AppDatabase.class.getSimpleName();
private static final Object LOCK=new Object();
private static final String DATABASE_NAME="todolist";
private static AppDatabase mInstance;
public static AppDatabase getInstance(Context context){
if(mInstance==null){
synchronized (LOCK){
Log.d(LOG_TAG,"Creating new database instance");
mInstance= Room.databaseBuilder(context.getApplicationContext(),
AppDatabase.class,AppDatabase.DATABASE_NAME)
.allowMainThreadQueries()
.build();
}
}
Log.d(LOG_TAG,"getting the database instance");
return mInstance;
}
public abstract TaskDao taskDao();
}
我的AddTaskActivity代码
public class AddTaskActivity extends AppCompatActivity {
// Extra for the task ID to be received in the intent
public static final String EXTRA_TASK_ID = "extraTaskId";
// Extra for the task ID to be received after rotation
public static final String INSTANCE_TASK_ID = "instanceTaskId";
// Constants for priority
public static final int PRIORITY_HIGH = 1;
public static final int PRIORITY_MEDIUM = 2;
public static final int PRIORITY_LOW = 3;
// Constant for default task id to be used when not in update mode
private static final int DEFAULT_TASK_ID = -1;
// Constant for logging
private static final String TAG = AddTaskActivity.class.getSimpleName();
// Fields for views
EditText mEditText;
RadioGroup mRadioGroup;
Button mButton;
private int mTaskId = DEFAULT_TASK_ID;
private AppDatabase mDb;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_task);
mDb=AppDatabase.getInstance(getApplicationContext());
initViews();
if (savedInstanceState != null && savedInstanceState.containsKey(INSTANCE_TASK_ID)) {
mTaskId = savedInstanceState.getInt(INSTANCE_TASK_ID, DEFAULT_TASK_ID);
}
Intent intent = getIntent();
if (intent != null && intent.hasExtra(EXTRA_TASK_ID)) {
mButton.setText(R.string.update_button);
if (mTaskId == DEFAULT_TASK_ID) {
// populate the UI
}
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
outState.putInt(INSTANCE_TASK_ID, mTaskId);
super.onSaveInstanceState(outState);
}
/**
* initViews is called from onCreate to init the member variable views
*/
private void initViews() {
mEditText = findViewById(R.id.editTextTaskDescription);
mRadioGroup = findViewById(R.id.radioGroup);
mButton = findViewById(R.id.saveButton);
mButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
onSaveButtonClicked();
}
});
}
/**
* populateUI would be called to populate the UI when in update mode
*
* @param task the taskEntry to populate the UI
*/
private void populateUI(TaskEntry task) {
}
/**
* onSaveButtonClicked is called when the "save" button is clicked.
* It retrieves user input and inserts that new task data into the underlying database.
*/
public void onSaveButtonClicked() {
// Not yet implemented
String description=mEditText.getText().toString();
int priority=getPriorityFromViews();
Date date=new Date();
TaskEntry taskEntry=new TaskEntry(description,priority,date);
mDb.taskDao().insertTask(taskEntry);
finish();
}
/**
* getPriority is called whenever the selected priority needs to be retrieved
*/
public int getPriorityFromViews() {
int priority = 1;
int checkedId = ((RadioGroup) findViewById(R.id.radioGroup)).getCheckedRadioButtonId();
switch (checkedId) {
case R.id.radButton1:
priority = PRIORITY_HIGH;
break;
case R.id.radButton2:
priority = PRIORITY_MEDIUM;
break;
case R.id.radButton3:
priority = PRIORITY_LOW;
}
return priority;
}
/**
* setPriority is called when we receive a task from MainActivity
*
* @param priority the priority value
*/
public void setPriorityInViews(int priority) {
switch (priority) {
case PRIORITY_HIGH:
((RadioGroup) findViewById(R.id.radioGroup)).check(R.id.radButton1);
break;
case PRIORITY_MEDIUM:
((RadioGroup) findViewById(R.id.radioGroup)).check(R.id.radButton2);
break;
case PRIORITY_LOW:
((RadioGroup) findViewById(R.id.radioGroup)).check(R.id.radButton3);
}
}
}