如何在android中从数据库中获取数据并在文本视图中显示

我正在创建一个包含数据库注册的android应用程序。在另一个活动中，我放置了一个按钮，用于从文本视图中显示的数据库检索数据。我做了一些类似的操作，但它显示了一个名为NoClassDefFoundError的错误。请帮我做这个。如果有任何错误，请原谅。提前谢谢。 这是我的主要活动：

package com.developer.and;


import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;

public class Modes extends Activity {

    Button auto,manual,adminsettings;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.modes);


        auto = (Button)findViewById(R.id.button_auto);
        auto.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                Intent auto = new Intent(Modes.this,Auto.class);
                startActivity(auto);
            }
        });

        manual = (Button)findViewById(R.id.button_manualmode);
        manual.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {

                Intent manual = new Intent(Modes.this,Manual.class);
                startActivity(manual);

            }
        });
        adminsettings = (Button)findViewById(R.id.button_Adminsettings);

        savedInstanceState = getIntent().getExtras();
        if(savedInstanceState!=null){
            String value_username = savedInstanceState.getString("USERNAME"); //getting username key,value pairs sent from previous intents

            String value_password = savedInstanceState.getString("PASSWORD"); //getting password key,value pairs sent from previous intents

            if(value_username.equals("medequip") && value_password.equals("medequip")){   //Comparing username and password sent from previous intent activity to display admin settings button or not...

            adminsettings.setVisibility(View.VISIBLE);                          //setting visibility for a button
            adminsettings.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    Intent retriving_database = new Intent (Modes.this,AdminSettings.class);
                    startActivity(retriving_database);

                }
            });


            }
            else
            adminsettings.setVisibility(View.GONE);
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.modes, 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();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

这是我获取数据库结果的第二个活动

package com.developer.and;

import android.database.Cursor;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import com.developer.milanandroid.LoginDataBaseAdapter;

public class AdminSettings extends ActionBarActivity {
    LoginDataBaseAdapter logindatabase_adapter_child;
    Button fetch_database;
    TextView text_fetched_database_results;
    String username,password;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.admin_settings);

        fetch_database = (Button)findViewById(R.id.Button_Fetch_Database);
        fetch_database.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Cursor c = logindatabase_adapter_child.db.rawQuery("select * from MilanloginRegistration", null);
                text_fetched_database_results.setText("");
                c.moveToFirst();
                do{
                    username = c.getString(c.getColumnIndex("USERNAME"));
                    password = c.getString(1);
                    text_fetched_database_results.append("USERNAME::-->"+username+"PASSWORD::-->"+password+"\n");

                }while(c.moveToNext());
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.admin_settings, 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();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

MainActivity.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.developer.and.Modes" >

   <Button
        android:id="@+id/button_Adminsettings"
        android:layout_width="450dp"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="@string/Adminsettings" />

</RelativeLayout>

---

您的类

AdminSetting

和

Mode

在包

com.developer.and

中，但不在

com.developer.milanandroid

中。更改两个文件第1行中的包名，编译器就可以找到该类。

您的类

AdminSettings

和

Modes

位于包

com.developer.和
中，而不是
com.developer.milanandroid
中。所以，要么在您的project explore中更改包名，要么在AndroidManifest中更改包名以相互匹配。目前在您的项目中，您有package
com.developer.和
，但在您的AndroidManifest中，您似乎正在使用package
com.developer.milanandroid
您是否在Manifest中声明了AdminSettins活动？是的，伙计@Opiatefuchssee是
AdminSettins
任何库类？没有dude@piyushgupta对不起dude formy project sake我在这篇文章中更改了包名实际上是com.developer.milanandroid在上面两个classes@Desmond对不起，伙计，为了我的项目，我在这篇文章中更改了包名，实际上是com.developer.milanandroid以上两类中有@Rajen Raiyarela
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.developer.and.AdminSettings" >

    <LinearLayout
        android:id="@+id/linearLayout1"
        android:layout_width="@dimen/Retriving_database_ll_width"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:orientation="vertical" >

        <Button
            android:id="@+id/Button_Fetch_Database"
            style="?android:attr/buttonStyleSmall"
            android:layout_width="@dimen/Retriving_database_Button_width"
            android:layout_height="wrap_content"
            android:text="@string/Retriving_database" />
    </LinearLayout>

    <ScrollView
        android:id="@+id/scrollView_db_contacts"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_toRightOf="@+id/linearLayout1" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical" >

            <TextView
                android:id="@+id/textView_fetched_database_results"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:textSize="20sp" />
        </LinearLayout>
    </ScrollView>

</RelativeLayout>

04-27 11:32:41.910: E/AndroidRuntime(13452): FATAL EXCEPTION: main
04-27 11:32:41.910: E/AndroidRuntime(13452): Process: com.developer.milanandroid, PID: 13452
04-27 11:32:41.910: E/AndroidRuntime(13452): java.lang.NoClassDefFoundError: com.developer.milanandroid.AdminSettings
04-27 11:32:41.910: E/AndroidRuntime(13452):    at com.developer.milanandroid.Modes$3.onClick(Modes.java:56)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at android.view.View.performClick(View.java:4438)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at android.view.View$PerformClick.run(View.java:18422)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at android.os.Handler.handleCallback(Handler.java:733)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at android.os.Handler.dispatchMessage(Handler.java:95)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at android.os.Looper.loop(Looper.java:136)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at android.app.ActivityThread.main(ActivityThread.java:5017)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at java.lang.reflect.Method.invokeNative(Native Method)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at java.lang.reflect.Method.invoke(Method.java:515)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-27 11:32:41.910: E/AndroidRuntime(13452):    at dalvik.system.NativeStart.main(Native Method)