我在登录 DialogFragment 中有一个复选框,我想用它来检查是否应该将输入的用户名添加到首选项中。但是当我使用复选框的 isChecked() 方法执行 if 时,我得到一个 NullPointerException。我添加了一个 try/catch 时钟,然后进一步尝试添加复选框的 toString 输出的 Log.d,再次出现 NullPointerException。因此,虽然很明显代码似乎无法识别当前范围内复选框的存在,但我无法弄清楚我看过的内容。它允许我使用 findViewById 创建一个 CheckBox 而不会出错。谢谢。
登录DialogFragment的源代码:
public class LoginDialogFragment extends DialogFragment {
public interface LoginDialogListener {
public void onDialogPositiveClick(DialogFragment dialog);
public void onDialogNegativeClick(DialogFragment dialog);
}
LoginDialogListener mListener;
public void onAttach(Activity activity) {
super.onAttach(activity);
// Verify that the host activity implements the callback interface
try {
// Instantiate the NoticeDialogListener so we can send events to the host
mListener = (LoginDialogListener) activity;
} catch (ClassCastException e) {
// The activity doesn't implement the interface, throw exception
throw new ClassCastException(activity.toString()
+ " must implement NoticeDialogListener");
}
}
public Dialog onCreateDialog(Bundle savedInstanceState) {
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
// Get the layout inflater
LayoutInflater inflater = getActivity().getLayoutInflater();
// Inflate and set the layout for the dialog
// Pass null as the parent view because its going in the dialog layout
builder.setView(inflater.inflate(R.layout.login_dialog, null))
// Add action buttons
.setPositiveButton("Login", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int id) {
// Send the positive button event back to the host activity
CheckBox loginCheckBox =
(CheckBox)getActivity().findViewById(R.id.input_chkbox);
try{
if(loginCheckBox.isChecked() == true){
mListener.onDialogPositiveClick(LoginDialogFragment.this);
}else{
mListener.onDialogNegativeClick(LoginDialogFragment.this);
}
}catch(Exception e){
Log.d(null, e.toString());
Log.d(null, loginCheckBox.toString()); // got
nullPointerException again when I added this line in catch block.
Toast eToast = Toast.makeText(getActivity(), "error in:
LoginDialogFragment.setPosButton.onClick", Toast.LENGTH_LONG);
eToast.show();
}
}
})
对话框片段的父活动源代码:
public class UsingPreferencesActivity
extends FragmentActivity
implements LoginDialogFragment.LoginDialogListener{
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
this.setContentView(R.layout.main);
this.showLoginDialog();
}
public void showLoginDialog() {
// Create an instance of the dialog fragment and show it
DialogFragment dialog = new LoginDialogFragment();
dialog.show(getSupportFragmentManager(), "LoginDialogFragment");
}
public void onDialogPositiveClick(DialogFragment dialog) {
Toast toast = Toast.makeText(getBaseContext(), "OK", Toast.LENGTH_LONG);
toast.show();
}
public void onDialogNegativeClick(DialogFragment dialog) {
Toast toast = Toast.makeText(getBaseContext(), "Cancel",
Toast.LENGTH_LONG);
toast.show();
}
public void onClickLoad(View view){
Intent i = new Intent("com.example.homework09.AppPreferenceActivity");
startActivity(i);
}
public void onClickDisplay(View view){
SharedPreferences appPrefs =
getSharedPreferences("com.example.homework09_preferences",MODE_PRIVATE);
DisplayText(appPrefs.getString("editTextPref", ""));
}
public void onClickModify(View view){
SharedPreferences appPrefs =
getSharedPreferences("com.example.homework09_preferences", MODE_PRIVATE);
SharedPreferences.Editor prefsEditor = appPrefs.edit();
prefsEditor.putString("editTextPref",
((EditText)findViewById(R.id.etNewUsername)).getText().toString());
prefsEditor.commit();
DisplayText(appPrefs.getString("editTextPref", ""));
}
public void onClickReset(View view){
SharedPreferences appPrefs =
getSharedPreferences("com.example.homework09_preferences", MODE_PRIVATE);
SharedPreferences.Editor prefsEditor = appPrefs.edit();
prefsEditor.putString("editTextPref", " ");
prefsEditor.commit();
DisplayText(appPrefs.getString("editTextPref", ""));
}
private void DisplayText(String str){
Toast.makeText(getBaseContext(), str, Toast.LENGTH_LONG).show();
TextView textView = (TextView)findViewById(R.id.tvUsername);
textView.setText(str);
}
}
DialogFragment (login_dialog.xml) 的布局:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<EditText
android:id="@+id/input"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="[Enter username here]"/>
<CheckBox
android:id="@+id/input_chkbox"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Save Username?"
android:defaultValue="false"
/>
</LinearLayout>