我在android中創建一個簡單的筆記應用程序。我基本上使用了兩個名爲主頁面和第二活動的活動類。我將一些數據存儲在第二個活動的共享首選項中,並希望在我的第一個活動中使用它。我將數據作爲(String,Integer)密鑰對存儲在共享首選項中。在我的主要活動類中,當我從Integer中獲取共享首選項的值並將其與值0進行比較時,發現java.lang.string不能轉換爲java.lang.integer。我不知道爲什麼這個例外即將到來。 Android工作室不給我一個例外,但當我運行我的應用程序,我的應用程序崩潰。我已附上代碼以供參考。獲取投射異常Android
MainActivity類別:
package com.example.prateeksharma.noteballondor;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
public class MainPage extends ActionBarActivity {
Notes notes = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_page);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main_page, menu);
return true;
}
@Override
protected void onResume() {
super.onResume();
SharedPreferences sharedPreferences = getSharedPreferences("com.example.prateeksharma.noteballondor", Context.MODE_PRIVATE);
//Map<String, Integer> notesMap = (Map<String, Integer>)sharedPreferences.getAll();
List<Notes> listNotes = new ArrayList<>();
Map<String, ?> prefsMap = sharedPreferences.getAll();
for (Map.Entry<String, ?> entry: prefsMap.entrySet()) {
if (entry.getValue() == 0){
notes = new Notes();
}
notes.setNoteText(entry.getKey());
listNotes.add(notes);
sharedPreferences.edit().putInt(entry.getKey(),2);
}
NotesArrayAdapter notesArrayAdapter = new NotesArrayAdapter(this,R.layout.list_layout, listNotes);
final ListView listview = (ListView) findViewById(R.id.listView);
listview.setAdapter(notesArrayAdapter);
listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
/**/
@Override
public void onItemClick(AdapterView<?> parent, final View view,
int position, long id) {
notes = (Notes) parent.getItemAtPosition(position);
Intent intent = new Intent(MainPage.this, SecondActivity.class);
intent.putExtra("Notes",notes);
startActivity(intent);
}
});
}
@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
switch (item.getItemId()) {
case R.id.new_link:
Intent intent = new Intent(this, SecondActivity.class);
intent.putExtra("Notes",(android.os.Parcelable)null);
startActivity(intent);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
}
SecondActivity類:
package com.example.prateeksharma.noteballondor;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;
public class SecondActivity extends ActionBarActivity {
public SharedPreferences sharedPreferences;
SharedPreferences.Editor edit;
Notes notes;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
sharedPreferences = getSharedPreferences("com.example.prateeksharma.noteballondor", Context.MODE_PRIVATE);
edit = sharedPreferences.edit();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_second, menu);
return true;
}
@Override
protected void onResume() {
super.onResume();
Intent intent = getIntent();
notes = (Notes)intent.getParcelableExtra("Notes");
EditText editText = (EditText) findViewById(R.id.editText);
if(notes != null){
editText.setText(notes.getNoteText());
}
else{
editText.setText(null);
}
}
@Override
protected void onStop() {
super.onStop();
getIntent().removeExtra(notes.getNoteText());
}
@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();
Intent intent = getIntent();
//noinspection SimplifiableIfStatement
switch (item.getItemId()) {
case R.id.save:
EditText editText = (EditText)findViewById(R.id.editText);
if (notes != null){
edit.putInt(String.valueOf(editText.getText()),1);
}
else{
edit.putInt(String.valueOf(editText.getText()),0);
}
edit.commit();
return true;
case R.id.delete:
if(notes != null){
edit.remove(notes.getNoteText());
edit.commit();
finish();
return true;
}
default:
return super.onOptionsItemSelected(item);
}
}
}
票據類,我使用的是:
package com.example.prateeksharma.noteballondor;
import android.os.Parcel;
import android.os.Parcelable;
/**
* Created by Dell on 02-06-2015.
*/
public class Notes implements Parcelable {
private String noteText;
public String getNoteText() {
return noteText;
}
public void setNoteText(String noteText) {
this.noteText = noteText;
}
private Notes(Parcel in) {
noteText = in.readString();
}
public Notes(){
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(noteText);
}
@SuppressWarnings("unused")
public static final Parcelable.Creator<Notes> CREATOR = new Parcelable.Creator<Notes>() {
@Override
public Notes createFromParcel(Parcel in) {
return new Notes(in);
}
@Override
public Notes[] newArray(int size) {
return new Notes[size];
}
};
}
誰能告訴我爲什麼這個錯誤發生在MainActivity類別來在該行 如果(entry.getValue()== 0)
謝謝。
這可能是因爲當你定義'地圖 prefsMap = sharedPreferences.getAll();'你包括所有存儲在您的SharedPrefe值的rences,其中包括您在'onOptionsItemSelected'方法中保存的'noteText'字符串,這肯定會導致ClassCastException,因爲您試圖將存儲在您的首選項中的每個項目都作爲整數進行投射。 –
Guardanis
@Guardians對不起..但我不明白你的答案。在第二個Activity類的onOptionsItemSelected方法中,我將key-pair值存儲爲sharedPreferences中的(String,Integer)。所以value應該總是整數。我正在使用sharedPreferece類的putInt方法。在主Activity類中,我正在執行Map.get(Key)以獲取應始終爲整數的值。如果我錯了,可以請你詳細說明你的答案或糾正我。 –