单击viewList中的项目..用数据库android中的数据打开新活动

时间：2013-11-25 07:49:48

标签： android eclipse listview android-sqlite onitemclicklistener

我有这个代码来显示我的图书数据库中的详细信息，当我点击列表中的另一个活动工作正常时... 我用这段代码来做.. 但它不起作用！ 谁能告诉我我的代码有什么问题？ 我希望当我点击项目时，它会转到详细信息活动并显示所选书籍的其余详细信息。 请帮忙 ：（ ！ 谢谢！

package com.example.test;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.widget.TextView;

public class BookDetails extends Activity {

protected TextView name;
protected TextView author;
protected TextView isbn;
protected TextView copy;
protected TextView info;
protected int bookId;
private DbHelper mHelper;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.book_details);

    bookId = getIntent().getIntExtra("bID", 0);
    SQLiteDatabase db = mHelper.getWritableDatabase();
    Cursor cursor = db.rawQuery("SELECT * FROM "+ DbHelper.TABLE_NAME, null);

    if (cursor.getCount() == 1)
    {
        cursor.moveToFirst();

        name = (TextView) findViewById(R.id.name);
        name.setText(cursor.getString(cursor.getColumnIndex("KEY_NAME")));

        author = (TextView) findViewById(R.id.author);
        author.setText(cursor.getString(cursor.getColumnIndex("KEY_AUTHOR")));

        isbn = (TextView) findViewById(R.id.isbn);
        isbn.setText(cursor.getString(cursor.getColumnIndex("KEY_ISBN")));

        copy = (TextView) findViewById(R.id.copy);
        copy.setText(cursor.getString(cursor.getColumnIndex("KEY_COPIES")));

        info = (TextView) findViewById(R.id.info);
        info.setText(cursor.getString(cursor.getColumnIndex("KEY_INFO")));

    }

}

}

这里是DisplayActivity.java 

 package com.example.test;


 import java.util.ArrayList;

 import android.app.Activity;
 import android.app.AlertDialog;
 import android.content.DialogInterface;
 import android.content.Intent;
 import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.os.Bundle;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.AdapterView;
 import android.widget.AdapterView.OnItemClickListener;
 import android.widget.AdapterView.OnItemLongClickListener;
 import android.widget.ListAdapter;
 import android.widget.ListView;
 import android.widget.Toast;

 public class DisplayActivity extends Activity {

private DbHelper mHelper;
private SQLiteDatabase dataBase;
private ListAdapter adapter;
private ArrayList<String> bookId = new ArrayList<String>();
private ArrayList<String> book_Name = new ArrayList<String>();
private ArrayList<String> book_Author = new ArrayList<String>();
private ArrayList<String> book_Info = new ArrayList<String>();
private ArrayList<String> book_Isbn = new ArrayList<String>();
private ArrayList<String> book_Copy = new ArrayList<String>();
public static String bNAME="bname";
public static String bAUTHOR="bauthor";
public static String bISBN="bisbn";
public static String bCOPY="bcopy";
public static String bINFO="binfo";
public static String bID="ID";
private ListView userList;
private AlertDialog.Builder build;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.display_activity);

    userList = (ListView) findViewById(R.id.List);

    mHelper = new DbHelper(this);
       userList.setOnItemClickListener(new OnItemClickListener() {
              public void onItemClick(AdapterView<?> parent, View view,int position, long id) {

                  Intent intent = new Intent(view.getContext(),BookDetails.class);
                Cursor cursor = (Cursor) adapter.getItem(position);
                intent.putExtra("bID", cursor.getInt(cursor.getColumnIndex("KEY_ID")));
                startActivity(intent);
              }
            });}

@Override
protected void onResume() {
    displayData();
    super.onResume();
}

/**
 * displays data from SQLite
 */
private void displayData() {
    dataBase = mHelper.getWritableDatabase();
    Cursor mCursor = dataBase.rawQuery("SELECT * FROM "
            + DbHelper.TABLE_NAME, null);

    bookId.clear();
    book_Name.clear();
    book_Author.clear();
    book_Isbn.clear();
    book_Copy.clear();
    book_Info.clear();
    if (mCursor.moveToFirst()) {
        do {
            bookId.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_ID)));
            book_Name.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_NAME)));
            book_Author.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_AUTHOR)));
            book_Isbn.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_ISBN)));
            book_Copy.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_COPIES)));
            book_Info.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_INFO)));

        } while (mCursor.moveToNext());
    }
    DisplayAdapter disadpt = new DisplayAdapter(DisplayActivity.this,bookId, book_Name);
    userList.setAdapter(disadpt);
    mCursor.close();
}


 }

这是我运行时获得的LogCat ,,, 

11-25 03:02:52.878: D/dalvikvm(2734): GC_FOR_ALLOC freed 59K, 4% free 3150K/3272K, paused 40ms, total 44ms
11-25 03:02:52.978: I/Choreographer(2734): Skipped 46 frames!  The application may be doing too much work on its main thread.
11-25 03:02:53.038: D/gralloc_goldfish(2734): Emulator without GPU emulation detected.
11-25 03:02:55.768: D/AndroidRuntime(2734): Shutting down VM
11-25 03:02:55.768: W/dalvikvm(2734): threadid=1: thread exiting with uncaught exception (group=0xb4a4bb90)
11-25 03:02:55.818: E/AndroidRuntime(2734): FATAL EXCEPTION: main
11-25 03:02:55.818: E/AndroidRuntime(2734): Process: com.example.test, PID: 2734
11-25 03:02:55.818: E/AndroidRuntime(2734): java.lang.NullPointerException
11-25 03:02:55.818: E/AndroidRuntime(2734):     at com.example.test.DisplayActivity$1.onItemClick(DisplayActivity.java:58)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at android.widget.AdapterView.performItemClick(AdapterView.java:299)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at android.widget.AbsListView.performItemClick(AbsListView.java:1113)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at android.widget.AbsListView$PerformClick.run(AbsListView.java:2904)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at android.widget.AbsListView$3.run(AbsListView.java:3638)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at android.os.Handler.handleCallback(Handler.java:733)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at android.os.Handler.dispatchMessage(Handler.java:95)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at android.os.Looper.loop(Looper.java:137)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at android.app.ActivityThread.main(ActivityThread.java:4998)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at java.lang.reflect.Method.invokeNative(Native Method)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at java.lang.reflect.Method.invoke(Method.java:515)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
11-25 03:02:55.818: E/AndroidRuntime(2734):     at dalvik.system.NativeStart.main(Native Method)

2 个答案:

答案 0 :(得分：0)

你应该在displayData()函数中onCreate，即

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.display_activity);

    userList = (ListView) findViewById(R.id.List);  

    mHelper = new DbHelper(this);
     displayData();

       userList.setOnItemClickListener(new OnItemClickListener() {
              public void onItemClick(AdapterView<?> parent, View view,int position, long id) {

                  Intent intent = new Intent(DisplayActivity.this,BookDetails.class);
                Cursor cursor = (Cursor) parent.getItem(position);
                intent.putExtra("bID", cursor.getInt(cursor.getColumnIndex("KEY_ID")));
                startActivity(intent);
              }
            });
}

答案 1 :(得分：0)

这里指出了问题：

11-25 03:02:55.818: E/AndroidRuntime(2734): java.lang.NullPointerException
11-25 03:02:55.818: E/AndroidRuntime(2734):     at com.example.test.DisplayActivity$1.onItemClick(DisplayActivity.java:58)

从您的代码可以清楚地看出private ListAdapter adapter;未在任何地方使用/初始化，而是初始化适配器DisplayAdapter disadpt = new DisplayAdapter(DisplayActivity.this,bookId, book_Name);，以便您可以更改适配器减速度以使用正确的减速度。

DisplayActivity代码：

public class DisplayActivity extends Activity {

private DbHelper mHelper;
private SQLiteDatabase dataBase;
private DisplayAdapter disadpt; // <--- one change here
private ArrayList<String> bookId = new ArrayList<String>();
private ArrayList<String> book_Name = new ArrayList<String>();
private ArrayList<String> book_Author = new ArrayList<String>();
private ArrayList<String> book_Info = new ArrayList<String>();
private ArrayList<String> book_Isbn = new ArrayList<String>();
private ArrayList<String> book_Copy = new ArrayList<String>();
public static String bNAME = "bname";
public static String bAUTHOR = "bauthor";
public static String bISBN = "bisbn";
public static String bCOPY = "bcopy";
public static String bINFO = "binfo";
public static String bID = "ID";
private ListView userList;
private AlertDialog.Builder build;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.display_activity);

    userList = (ListView) findViewById(R.id.List);

    mHelper = new DbHelper(this);
    userList.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            if(disadpt == null) return; // avoid crashes if not initialized
            Intent intent = new Intent(DisplayActivity.this, BookDetails.class); // <-- better use activity context
            Cursor cursor = (Cursor) disadpt.getItem(position);
            intent.putExtra("bID", cursor.getInt(cursor.getColumnIndex(DbHelper.KEY_ID))); // <--- also this seems faulty you do not have any column named "KEY_ID"
            startActivity(intent);
        }
    });
}

@Override
protected void onResume() {
    displayData();
    super.onResume();
}

/**
 * displays data from SQLite
 */
private void displayData() {
    dataBase = mHelper.getWritableDatabase();
    Cursor mCursor = dataBase.rawQuery("SELECT * FROM "
            + DbHelper.TABLE_NAME, null);

    bookId.clear();
    book_Name.clear();
    book_Author.clear();
    book_Isbn.clear();
    book_Copy.clear();
    book_Info.clear();
    if (mCursor.moveToFirst()) {
        do {
            bookId.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_ID)));
            book_Name.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_NAME)));
            book_Author.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_AUTHOR)));
            book_Isbn.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_ISBN)));
            book_Copy.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_COPIES)));
            book_Info.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_INFO)));

        } while (mCursor.moveToNext());
    }
  // Another change here v
    disadpt = new DisplayAdapter(DisplayActivity.this, bookId, book_Name);
    userList.setAdapter(disadpt);
    mCursor.close();
}

}
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