共享首选项

Question

我正在尝试在我的应用中使用SharedPrefs，我只想从单独的设置活动中检索电子邮件地址和密码。我已经实施了

package com.overclockerz.webtest;

import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.widget.EditText;

public class SettingScreen extends Activity {
    static EditText username;
    static EditText password;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.setting_screen);
    username = (EditText) findViewById(R.id.username);
    password = (EditText) findViewById(R.id.password);

    SharedPreferences settings =  
            getSharedPreferences("APP_PREFS", MODE_PRIVATE); 
    SharedPreferences.Editor prefEditor = settings.edit();
    prefEditor.putString("Username", username.getText().toString());
    prefEditor.putString("Password", username.getText().toString());
    prefEditor.commit();        

}

}

我试图检索 包com.overclockerz.webtest;

import org.apache.http.util.EncodingUtils;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.webkit.CookieManager;
import android.webkit.WebSettings;
import android.webkit.WebSettings.LayoutAlgorithm;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;

public class MainActivity extends Activity implements OnItemSelectedListener,
        OnClickListener {
String query = "fldUsername=" + username + "&fldPassword=" + password + "&ut=3";
String username = prefs.getString("Username");
String password = getText(R.id.password).toString();

    @SuppressLint("SetJavaScriptEnabled")
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this); 
        // then you use
        prefs.getBoolean("keystring", true);
        //there are also methods to put strings,float, longs, ints





        WebView myWebView = (WebView) findViewById(R.id.webview);
        WebSettings webSettings = myWebView.getSettings();
        webSettings.setJavaScriptEnabled(true);
        webSettings.setUserAgentString("SMUK");
        //myWebView.setInitialScale(100);
        //myWebView.setPadding(0, 0, 0, 0);
        CookieManager.getInstance().setAcceptCookie(true);

        // webSettings.setUseWideViewPort(true);
        webSettings.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);
        myWebView.setWebViewClient(new WebViewClient());
        myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                EncodingUtils.getBytes(query,"BASE64"));
        Toast.makeText(getApplicationContext(), query, Toast.LENGTH_LONG)
         .show();
        Spinner spinner = (Spinner) findViewById(R.id.menu_spinner);
        // Create an ArrayAdapter using the string array and a default spinner
        // layout
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                this, R.array.spinner_links,
                android.R.layout.simple_spinner_item);
        // Specify the layout to use when the list of choices appears
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        // Apply the adapter to the spinner
        spinner.setAdapter(adapter);

        spinner.setOnItemSelectedListener(this);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        WebView myWebView = (WebView) findViewById(R.id.webview);
        // Check if the key event was the Back button and if there's history
        if ((keyCode == KeyEvent.KEYCODE_BACK) && myWebView.canGoBack()) {
            myWebView.goBack();
            return true;
        }
        // If it wasn't the Back key or there's no web page history, bubble up
        // to the default
        // system behavior (probably exit the activity)
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;

    }

    @Override
    public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
            long arg3) {
        WebView myWebView = (WebView) findViewById(R.id.webview);
        switch (arg2) {
        case 0:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView.loadUrl("http://test.schoolmilkuk.co.uk/parent-home");
            break;
        case 1:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView
                    .loadUrl("http://test.schoolmilkuk.co.uk/parent-change-pass");
            break;
        case 2:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView
                    .loadUrl("http://test.schoolmilkuk.co.uk/parent-add-child");
            break;
        case 3:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView
                    .loadUrl("http://test.schoolmilkuk.co.uk/parent-children-list");
            break;
        case 4:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView.loadUrl("http://test.schoolmilkuk.co.uk/parent-order");
            break;
        case 5:
            myWebView.clearCache(true);
            Toast.makeText(getApplicationContext(), "Cache Cleared :)",
                    Toast.LENGTH_LONG).show();
            break;
        default:
            myWebView.loadUrl("http://test.schoolmilkuk.co.uk/parent-home");
            break;
        }
    }

    @Override
    public void onNothingSelected(AdapterView<?> arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.settings_menu:
            startActivity(new Intent(this, SettingScreen.class));
            return true;
        default:
            return super.onOptionsItemSelected(item);
        }
    }

}

String username = prefs.getString（“Username”，“Username”）没有意义，因为它没有使用用户设置的变量，因为你提供“用户名”？我非常困惑。

关注Blackbelt的建议（其中非常感谢）我将代码修改为并且我看到空指针异常？

package com.overclockerz.webtest;

import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.widget.EditText;

public class SettingScreen extends Activity {
    static EditText username;
    static EditText password;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.setting_screen);
        username = (EditText) findViewById(R.id.username);
        password = (EditText) findViewById(R.id.password);

        SharedPreferences settings =  
                getSharedPreferences("APP_PREFS", MODE_PRIVATE); 
        SharedPreferences.Editor prefEditor = settings.edit();
        prefEditor.putString("Username", username.getText().toString());
        prefEditor.putString("Password", username.getText().toString());
        prefEditor.commit();        

    }

}

package com.overclockerz.webtest;

import org.apache.http.util.EncodingUtils;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.webkit.CookieManager;
import android.webkit.WebSettings;
import android.webkit.WebSettings.LayoutAlgorithm;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;

public class MainActivity extends Activity implements OnItemSelectedListener,
        OnClickListener {
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
String username = prefs.getString("Username", "default");
String password = prefs.getString("Password", "default");

String query = "fldUsername=" + username + "&fldPassword=" + password + "&ut=3";
    @SuppressLint("SetJavaScriptEnabled")
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);



        WebView myWebView = (WebView) findViewById(R.id.webview);
        WebSettings webSettings = myWebView.getSettings();
        webSettings.setJavaScriptEnabled(true);
        webSettings.setUserAgentString("SMUK");
        //myWebView.setInitialScale(100);
        //myWebView.setPadding(0, 0, 0, 0);
        CookieManager.getInstance().setAcceptCookie(true);

        // webSettings.setUseWideViewPort(true);
        webSettings.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);
        myWebView.setWebViewClient(new WebViewClient());
        myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                EncodingUtils.getBytes(query,"BASE64"));
        Toast.makeText(getApplicationContext(), query, Toast.LENGTH_LONG)
         .show();
        Spinner spinner = (Spinner) findViewById(R.id.menu_spinner);
        // Create an ArrayAdapter using the string array and a default spinner
        // layout
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                this, R.array.spinner_links,
                android.R.layout.simple_spinner_item);
        // Specify the layout to use when the list of choices appears
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        // Apply the adapter to the spinner
        spinner.setAdapter(adapter);

        spinner.setOnItemSelectedListener(this);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        WebView myWebView = (WebView) findViewById(R.id.webview);
        // Check if the key event was the Back button and if there's history
        if ((keyCode == KeyEvent.KEYCODE_BACK) && myWebView.canGoBack()) {
            myWebView.goBack();
            return true;
        }
        // If it wasn't the Back key or there's no web page history, bubble up
        // to the default
        // system behavior (probably exit the activity)
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;

    }

    @Override
    public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
            long arg3) {
        WebView myWebView = (WebView) findViewById(R.id.webview);
        switch (arg2) {
        case 0:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView.loadUrl("http://test.schoolmilkuk.co.uk/parent-home");
            break;
        case 1:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView
                    .loadUrl("http://test.schoolmilkuk.co.uk/parent-change-pass");
            break;
        case 2:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView
                    .loadUrl("http://test.schoolmilkuk.co.uk/parent-add-child");
            break;
        case 3:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView
                    .loadUrl("http://test.schoolmilkuk.co.uk/parent-children-list");
            break;
        case 4:
            myWebView.postUrl("http://test.schoolmilkuk.co.uk/parents-login",
                    EncodingUtils.getBytes(query,"BASE64"));
            myWebView.loadUrl("http://test.schoolmilkuk.co.uk/parent-order");
            break;
        case 5:
            myWebView.clearCache(true);
            Toast.makeText(getApplicationContext(), "Cache Cleared :)",
                    Toast.LENGTH_LONG).show();
            break;
        default:
            myWebView.loadUrl("http://test.schoolmilkuk.co.uk/parent-home");
            break;
        }
    }

    @Override
    public void onNothingSelected(AdapterView<?> arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.settings_menu:
            startActivity(new Intent(this, SettingScreen.class));
            return true;
        default:
            return super.onOptionsItemSelected(item);
        }
    }

}

Answer 1

PreferenceManager.getDefaultSharedPreferences

和

SharedPreferences settings =  
            getSharedPreferences("APP_PREFS", MODE_PRIVATE); 

返回不同的东西。

前者将使用默认文件名（类似于您的pakage名称），后者将需要一个名称。所以不要混淆。 getString()的第二个参数是默认值。例如，您可以使用它来检查某些调味品是否不符合。

Answer 2

重新阅读getString的文档。仅当首选项中没有值时，它才会返回defValue。您可以将null作为第二个参数传递。如果你得到null，则表示尚未设置用户名。
此外，您应该将用户名保存到某些操作的首选项，而不是onCreate。例如。创建按钮“确定”并在onClick中为此按钮保存用户名。

Answer 3

如果您需要多个共享首选项，请在其中添加一些名称。

SharedPreferences sp = getApplication().getSharedPreferences("someName", Context.MODE_PRIVATE); 

如果你只需要一个

SharedPrefrences sp = PreferenceManager.getDefaultSharedPreferences(this);