好吧，我创建了一个应用程序，程序中有一个警报对话框。在代码中，它不会显示错误。但是当我运行它时，我看到了这个 Null 指针异常错误。我尝试解决它但仍然无法正常工作。我想要做的是，当用户单击删除按钮时，会出现一个警告对话框，提示“您确定要删除所选项目吗？” 当用户单击“是”时，它将被删除，如果“否”，则不会被删除。
这是我的代码：
主要活动文件：
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.pass_list);
hideKeyboard();
initializing();
show_list_layout();
Button logout = (Button) findViewById(R.id.button1);
String username = getIntent().getStringExtra("USERNAME");
Toast.makeText(PasswordActivity.this, "Welcome " + username, Toast.LENGTH_LONG).show();
logout.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent i = new Intent(PasswordActivity.this, LogIn.class);
startActivityForResult(i,0);
}
});
btn_del.setOnClickListener(this);
}
public void btn_addnew_click(View v){
this.selected_website = null;
show_add_layout();
}
public void btn_back_click(View v){
this.selected_website = null;
show_list_layout();
}
public void btn_edit_click(View v){
if(this.selected_website != null){
show_add_layout();
}else{
show_mesg("Please select item to edit.");
}
}
public void btn_add_update_click(View v){
hideKeyboard();
String username = getIntent().getStringExtra("USERNAME");
String str_sitename = this.edt_sitename.getText().toString();
String str_username = this.edt_username.getText().toString();
String str_password = this.edt_password.getText().toString();
if (str_sitename.equals("")){
//edt_sitename.requestFocus();
show_mesg("Please insert sitename.");
}else if (str_username.equals("")){
//edt_username.requestFocus();
show_mesg("Please insert username.");
}else if (str_password.equals("")){
//edt_password.requestFocus();
show_mesg("Please insert password.");
}else{
if (selected_website!=null){
selected_website.setUser(username);
selected_website.setSitename(str_sitename);
selected_website.setUsername(str_username);
selected_website.setPassword(str_password);
datasource.updateWebsite(selected_website);
show_mesg(str_sitename + " updated.");
hideKeyboard();
selected_website = null;
show_list_layout();
}else{
datasource.addWebsite(username, str_sitename,str_username,str_password);
hideKeyboard();
show_mesg(str_sitename + " added.");
selected_website = null;
show_add_layout();
}
}
}
public void popUps(){
if(this.selected_website != null){
DialogInterface.OnClickListener dialogClickListener = new DialogInterface.OnClickListener() {
private WebsiteRecords selected_website;
public void onClick(DialogInterface dialog, int which) {
switch (which){
case DialogInterface.BUTTON_POSITIVE:
datasource.deleteWebsite(this.selected_website);
hideKeyboard();
show_mesg(this.selected_website.getSitename() + " deleted.");
selected_website = null;
show_list_layout();
case DialogInterface.BUTTON_NEGATIVE:
show_mesg("NO");
break;
}
}
};
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Are you sure?")
.setPositiveButton("Yes", dialogClickListener)
.setNegativeButton("No", dialogClickListener)
.show();
}
else{
show_mesg("Please select item to delete.");
}
}
/*public void btn_del_click(View v){
if(this.selected_website != null){
datasource.deleteWebsite(this.selected_website);
hideKeyboard();
show_mesg(this.selected_website.getSitename() + " deleted.");
selected_website = null;
show_list_layout();
}else{
show_mesg("Please select item to delete.");
}
DialogInterface.OnClickListener dialogClickListener = new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
switch (which){
case DialogInterface.BUTTON_POSITIVE:
show_mesg("YES");
break;
case DialogInterface.BUTTON_NEGATIVE:
show_mesg("NO");
break;
}
}
};
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Are you sure?").setPositiveButton("Yes", dialogClickListener);
}*/
public class select_item_click implements OnClickListener{
private RadioButton rdb_select_item;
private WebsiteRecords website;
select_item_click(RadioButton rdb_select_item,WebsiteRecords website){
this.rdb_select_item = rdb_select_item;
this.website = website;
}
@Override
public void onClick(View v) {
for (int i = 0 ; i< all_radiobutton.size();i++){
RadioButton rdb_select_item = all_radiobutton.get(i);
rdb_select_item.setChecked(false);
}
selected_website = this.website;
this.rdb_select_item.setChecked(true);
}
}
public void hideKeyboard(){
this.getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);
}
public void show_add_layout(){
hideKeyboard();
LinearLayout layout_list = (LinearLayout)findViewById(R.id.layout_list);
LinearLayout layout_add = (LinearLayout)findViewById(R.id.layout_add_edit);
layout_list.setVisibility(View.GONE);
layout_add.setVisibility(View.VISIBLE);
if (selected_website != null){
this.edt_sitename.setText(selected_website.getSitename());
this.edt_username.setText(selected_website.getUsername());
this.edt_password.setText(selected_website.getPassword());
this.btn_add.setText("Update");
}else{
this.edt_sitename.setText("");
this.edt_username.setText("");
this.edt_password.setText("");
this.edt_sitename.requestFocus();
this.btn_add.setText("Add");
}
}
public void show_mesg(String msg){
Toast.makeText(getApplicationContext(),msg,Toast.LENGTH_SHORT).show();
}
public void show_list_layout(){
hideKeyboard();
LinearLayout layout_list = (LinearLayout)findViewById(R.id.layout_list);
LinearLayout layout_add = (LinearLayout)findViewById(R.id.layout_add_edit);
layout_list.setVisibility(View.VISIBLE);
layout_add.setVisibility(View.GONE);
this.tmp_websites = datasource.getAllWebsite(getIntent().getStringExtra("USERNAME"));
Log.i("algo","Cantid ad de web sites "+this.tmp_websites.size());
this.all_radiobutton.clear();
ListView showlist = (ListView) findViewById(R.id.ListWebsite);
showlist.removeAllViewsInLayout();
showlist.setAdapter(new WebsiteItemAdapter(this, android.R.layout.simple_list_item_checked, this.tmp_websites));
}
public class WebsiteItemAdapter extends ArrayAdapter<WebsiteRecords> {
private List<WebsiteRecords> websites;
public WebsiteItemAdapter(Context context, int textViewResourceId, List<WebsiteRecords> websites) {
super(context, textViewResourceId, websites);
this.websites = websites;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View view = convertView;
hideKeyboard();
WebsiteRecords website = websites.get(position);
if (website != null) {
LayoutInflater vi = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view = vi.inflate(R.layout.listview, null);
hideKeyboard();
RadioButton rdb_select_item =(RadioButton) view.findViewById(R.id.rdb_select_item);
LinearLayout layout_item = (LinearLayout) view.findViewById(R.id.layout_item);
TextView tv_sitename = (TextView) view.findViewById(R.id.website);
TextView tv_username = (TextView) view.findViewById(R.id.username);
TextView tv_password = (TextView) view.findViewById(R.id.password);
tv_sitename.setText(website.getSitename());
tv_username.setText("Username : " + website.getUsername() );
tv_password.setText("Password : " + website.getPassword());
if(selected_website != null){
if (selected_website.getId() == website.getId()) rdb_select_item.setChecked(true);
}
all_radiobutton.add(rdb_select_item);
rdb_select_item.setOnClickListener(new select_item_click(rdb_select_item,website));
layout_item.setOnClickListener(new select_item_click(rdb_select_item,website));
}
return view;
}
}
@Override
protected void onResume() {
datasource.open();
super.onResume();
}
@Override
protected void onPause() {
datasource.close();
super.onPause();
}
@Override
public void onClick(View v) {
if(v == btn_del) {
if(this.selected_website != null){
DialogInterface.OnClickListener dialogClickListener = new DialogInterface.OnClickListener() {
private WebsiteRecords selected_website;
public void onClick(DialogInterface dialog, int which) {
switch (which){
case DialogInterface.BUTTON_POSITIVE:
datasource.deleteWebsite(this.selected_website);
hideKeyboard();
show_mesg(this.selected_website.getSitename() + " deleted.");
selected_website = null;
show_list_layout();
case DialogInterface.BUTTON_NEGATIVE:
show_mesg("NO");
break;
}
}
};
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Are you sure?")
.setPositiveButton("Yes", dialogClickListener)
.setNegativeButton("NO", dialogClickListener)
.show();
show_mesg("PASSED");
}
else{
show_mesg("Please select item to delete.");
}
}
}
}
我的数据源文件：
public class DataSource {
private SQLiteDatabase database;
private MySQLiteHelper dbHelper;
private String[] allColumns = {
MySQLiteHelper.COLUMN_ID,
MySQLiteHelper.COLUMN_USER,
MySQLiteHelper.COLUMN_URL,
MySQLiteHelper.COLUMN_USERNAME,
MySQLiteHelper.COLUMN_PASSWORD
};
public DataSource(Context context) {
dbHelper = new MySQLiteHelper(context);
}
public void open() throws SQLException {
database = dbHelper.getWritableDatabase();
}
public void close() {
dbHelper.close();
}
public void addWebsite(String user, String sitename, String username, String password) {
ContentValues values = new ContentValues();
values.put(MySQLiteHelper.COLUMN_USER, user);
values.put(MySQLiteHelper.COLUMN_URL, sitename);
values.put(MySQLiteHelper.COLUMN_USERNAME, username);
values.put(MySQLiteHelper.COLUMN_PASSWORD, password);
database.insert(MySQLiteHelper.TABLE_URL, null,values);
}
public void updateWebsite(WebsiteRecords website){
ContentValues values = new ContentValues();
values.put(MySQLiteHelper.COLUMN_URL, website.getSitename());
values.put(MySQLiteHelper.COLUMN_USERNAME, website.getUsername());
values.put(MySQLiteHelper.COLUMN_PASSWORD, website.getPassword());
database.update(MySQLiteHelper.TABLE_URL, values, MySQLiteHelper.COLUMN_ID + " = " + website.getId(), null);
}
public void deleteWebsite(WebsiteRecords website) {
database.delete(MySQLiteHelper.TABLE_URL, MySQLiteHelper.COLUMN_ID + " = " + website.getId(), null);
}
public List<WebsiteRecords> getAllWebsite(String user){
List<WebsiteRecords> websites = new ArrayList<WebsiteRecords>();
Cursor cursor = database.rawQuery("SELECT * FROM " + MySQLiteHelper.TABLE_URL + " WHERE user='" + user+"'", null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
WebsiteRecords website = cursorToWebsite(cursor);
websites.add(website);
cursor.moveToNext();
}
cursor.close();
return websites;
}
private WebsiteRecords cursorToWebsite(Cursor cursor) {
WebsiteRecords website = new WebsiteRecords();
website.setId(cursor.getInt(0));
website.setUser(cursor.getString(1));
website.setSitename(cursor.getString(2));
website.setUsername(cursor.getString(3));
website.setPassword(cursor.getString(4));
return website;
}
你能帮我解决问题吗？
编辑 所以这里是LogCat：
01-31 08:11:07.649: E/AndroidRuntime(777): FATAL EXCEPTION: main
01-31 08:11:07.649: E/AndroidRuntime(777): java.lang.NullPointerException
01-31 08:11:07.649: E/AndroidRuntime(777): at com.bernadette.remembermypassword.DataSource.deleteWebsite(DataSource.java:56)
01-31 08:11:07.649: E/AndroidRuntime(777): at com.bernadette.remembermypassword.PasswordActivity$3.onClick(PasswordActivity.java:296)
01-31 08:11:07.649: E/AndroidRuntime(777): at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
01-31 08:11:07.649: E/AndroidRuntime(777): at android.os.Handler.dispatchMessage(Handler.java:99)
01-31 08:11:07.649: E/AndroidRuntime(777): at android.os.Looper.loop(Looper.java:137)
01-31 08:11:07.649: E/AndroidRuntime(777): at android.app.ActivityThread.main(ActivityThread.java:4745)
01-31 08:11:07.649: E/AndroidRuntime(777): at java.lang.reflect.Method.invokeNative(Native Method)
01-31 08:11:07.649: E/AndroidRuntime(777): at java.lang.reflect.Method.invoke(Method.java:511)
01-31 08:11:07.649: E/AndroidRuntime(777): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
01-31 08:11:07.649: E/AndroidRuntime(777): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-31 08:11:07.649: E/AndroidRuntime(777): at dalvik.system.NativeStart.main(Native Method)
01-31 08:30:21.998: E/Trace(827): error opening trace file: No such file or directory (2)