我收到错误：
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
尝试在片段中设置textView的文本时（在方法changeText中）
这是我的片段代码
public class MainFragment extends Fragment {
String date;
TextView infoText2;
public MainFragment() {
// Required empty public constructor
}
public Boolean daily;
//instantiate variables
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootview = inflater.inflate(R.layout.fragment_main, container, false);
infoText2 = (TextView) rootview.findViewById(R.id.infoText2);
//TODO THIS COULD POSSIBLY BE A PROBLEM TOO
//calls setdate function
startup(rootview);
btnClick(rootview);
return rootview;
}
public void startup(View v) {
date = new SimpleDateFormat("dd/MM/yyyy").format(new Date());
//gets the current date
TextView textView = (TextView) v.findViewById(R.id.infoText);
textView.setText(date);
//finds and replaces text in textView
SeekBar seekBar = (SeekBar) v.findViewById(R.id.seekBar2);
seekBar.setProgress(5);
seekBar.setMax(10);
//sets the seekbar progress
//BEGIN CHECKING IF USER HAS ADDED ENTRY
//TODO ADD IF ENTRY NOT COMPLETED STATEMENT
}
public void changeText(String mText) {
//TODO FIX THIS PROBLEM
infoText2.setText(mText);
//runs getTheData method
}
public void btnClick(View v) {
Button clickButton = (Button) v.findViewById(R.id.btnRate);
clickButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(MainFragment.this.getActivity(), "Rating successful", Toast.LENGTH_SHORT).show();
//conformation toast
SeekBar seekBar = (SeekBar) MainFragment.this.getActivity().findViewById(R.id.seekBar2);
seekBar.setEnabled(false);
Button btnRate = (Button) MainFragment.this.getActivity().findViewById(R.id.btnRate);
btnRate.setEnabled(false);
//disable seekbar and button
daily = true;
//marks rating complete for the day
//TODO reset complete back to false the next day
int value = seekBar.getProgress();
TextView ratingDisplay = (TextView) MainFragment.this.getActivity().findViewById(R.id.ratingText);
ratingDisplay.setText("Rating: " + Integer.toString(value) + " out of 10");
//sets the rating display to the value of the seekbar
((MainActivity) getActivity()).writeText(date, Integer.toString(value));
//Runs writeText method
((MainActivity) getActivity()).getTheData();
}
});
这里也是我的MainActivity的代码
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
NavigationView navigationView = null;
Toolbar toolbar = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
//sets the initial fragment
MainFragment fragment = new MainFragment();
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.commit();
//sets up the navigation drawer
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
/*public void rateOnClickListener(){
Button btnNavigator = (Button)findViewById(R.id.btnRate);
btnNavigator.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
MainFragment fragment = new MainFragment();
MainFragment.rate(v);
Toast.makeText(MainActivity.this, "yes", Toast.LENGTH_LONG);
}
});
}*/
//if the user presses the back button when the navdrawer is open
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_camera) {
MainFragment fragment = new MainFragment();
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.commit();
} else if (id == R.id.nav_gallery) {
SecondFragment fragment = new SecondFragment();
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
public void writeText(String timestamp, String rating) {
String my_results = rating + ", " + timestamp + "\n";
// String my results contains the date/time and the my_total score
String file_name = "fresh_3";
try {
FileOutputStream fileOutputStream = openFileOutput(file_name, MODE_APPEND | MODE_PRIVATE);
fileOutputStream.write(my_results.getBytes());
fileOutputStream.close();
Toast.makeText(getApplicationContext(), my_results + " success", Toast.LENGTH_LONG).show();
} catch(FileNotFoundException e) {
e.printStackTrace();
} catch(IOException e) {
e.printStackTrace();
}
//saves values to file
}
public void getTheData() {
try {
String Message;
String myData;
int i = 0;
FileInputStream fileInputStream = openFileInput("fresh_3");
InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
StringBuilder stringBuilder = new StringBuilder();
while ((Message = bufferedReader.readLine()) != null) {
stringBuilder.append(Message + "\n");
i++; //counter for the array to sort the data
}
//put data in a string with lines
fileInputStream.close();
myData = stringBuilder.toString(); // old successful method to output - need to count the lines
//instantiate the array
String mylines[] = new String[i]; //assigning number of lines to new array as Java cannot make a indeterminate array
mylines = myData.split("\\n");
Arrays.sort(mylines, Collections.reverseOrder()); //sort the array in order of first character - reverse order - descending
//remove the dodgy brackets and print the sorted data
MainFragment mainFragment = new MainFragment();
mainFragment.changeText(Arrays.toString(mylines).replaceAll("\\[|\\]", "")); //write the sorted data using regex (regular expression)
//infoText2.setVisibility(View.VISIBLE);
Toast.makeText(getApplicationContext(), "Number of records " + i, Toast.LENGTH_LONG).show(); //shows line number
} catch(FileNotFoundException e) {
e.printStackTrace();
} catch(IOException e) {
e.printStackTrace();
}
}
}
我已经尝试了各种方法来解决这个问题，包括getActivity()前面的findViewById以及rootview.。我已经将他们重新安排在不同的位置，但没有任何工作。
看来除了.setText之外的所有内容都有效，但如果有人能告诉我为什么拒绝合作，我会非常感激。
答案 0 :(得分：0)
onCreateView运行时，片段未附加到活动。要确保它正常工作，请在片段的OnResume（）中调用所需的函数。
例如：
gridview_left = (GridView)getView().findViewById(R.id.gridview_left);
答案 1 :(得分：0)
尝试在onActivityCreated（）...
中转移btnClick(rootview)调用
我认为片段尚未附加到活动
答案 2 :(得分：0)
@Override public void start(Stage primaryStage) { ProgressIndicator progressIndicator = new ProgressIndicator(); Button btn = new Button("Go"); VBox root = new VBox(10, btn, progressIndicator); btn.setOnAction((ActionEvent event) -> { Task<LineChart> task = new Task<LineChart>() { @Override protected LineChart call() throws Exception { for (int i = 0; i < 10; i++) { try { // do some work Thread.sleep(500); } catch (InterruptedException ex) { } updateProgress(10 * i, 100); } updateProgress(100, 100); return new LineChart(new NumberAxis(), new NumberAxis()); } }; progressIndicator.progressProperty().bind(task.progressProperty()); task.setOnSucceeded(evt -> { // handle successful completion of task on application thread root.getChildren().set(root.getChildren().indexOf(progressIndicator), task.getValue()); }); new Thread(task).start(); }); Scene scene = new Scene(root, 300, 300); primaryStage.setScene(scene); primaryStage.show(); }
当您在此处调用片段上的方法时，没有任何片段生命周期方法（如MainFragment mainFragment = new MainFragment();
mainFragment.changeText(Arrays.toString(mylines).replaceAll("\\[|\\]", ""));
）已运行。您需要等待执行片段事务。
更好的想法是使用参数onCreateView()将参数传递给您的片段，并在生命周期方法中读取片段本身中的参数。