Question

我是Android开发的新手，在这里我尝试使用sqlite创建一个简单的数据库应用程序我想要做的是当用户选择搜索它将要求id并且匹配id的相应数据应该替换该特定数据的editText字段

ActivityMain.xml

    <?xml version="1.0" encoding="utf-8"?>


<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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.ashish.project.MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Personal Details"
        android:id="@+id/textView"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:gravity="center" />
<ScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">
    <GridLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/gridLayout"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true">

        <LinearLayout
            android:orientation="horizontal"
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:layout_row="0"
            android:layout_column="0">

            <EditText
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:inputType="textPersonName"
                android:ems="10"
                android:id="@+id/editText"
                android:layout_weight="1"
                android:hint="First Name" />

            <EditText
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:inputType="textPersonName"
                android:ems="10"
                android:id="@+id/editText_LastName"
                android:layout_weight="1"
                android:hint="Last Name" />
        </LinearLayout>

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="number"
            android:ems="10"
            android:id="@+id/editText_number"
            android:layout_row="1"
            android:layout_column="0"
            android:hint="Contact Number" />

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="textEmailAddress"
            android:ems="10"
            android:id="@+id/editText_email"
            android:layout_row="2"
            android:layout_column="0"
            android:hint="E-mail" />

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_row="3"
            android:layout_column="0">

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Submit Details"
                android:id="@+id/Button_Submit"
                android:layout_weight="1"
                android:layout_row="4"
                android:layout_column="0" />

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Show Details"
                android:id="@+id/button_Show_Details"
                android:layout_gravity="right"
                android:layout_weight="1"
                android:layout_row="5"
                android:layout_column="0"
                android:layout_alignParentTop="true"
                android:layout_alignParentRight="true"
                android:layout_alignParentEnd="true" />
            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:id="@+id/button_search"
                android:layout_below="@id/Button_Submit"
                android:text="search"/>

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Clear Table"
                android:id="@+id/button_clear"
                android:gravity="left|center_horizontal"
                android:layout_below="@+id/button_Show_Details"
                android:layout_alignParentRight="true"
                android:layout_alignParentEnd="true" />
        </RelativeLayout>

    </GridLayout>

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="number"
        android:ems="10"
        android:id="@+id/editText_srch"
        android:hint="Enter id to search"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="search"
        android:id="@+id/button_show_id_result"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" />
        </RelativeLayout>
    </LinearLayout>
</ScrollView>
</RelativeLayout>

MainActivity.java

   package com.example.ashish.project;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.inputmethod.InputMethodManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    Button button_submit,button_show_details,button_clear,button_search,button_show_id_result;
    EditText firstName,lastName,number,email,editText_id_search;
    String firstnameString,lastnameString,emailString,num;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button_submit=(Button)findViewById(R.id.Button_Submit);
        button_show_id_result=(Button) findViewById(R.id.button_show_id_result);
        editText_id_search=(EditText) findViewById(R.id.editText_srch);
        button_show_details=(Button)findViewById(R.id.button_Show_Details);
        firstName=(EditText)findViewById(R.id.editText);
        button_search=(Button) findViewById(R.id.button_search);
        button_clear=(Button)findViewById(R.id.button_clear);
        lastName=(EditText)findViewById(R.id.editText_LastName);
        number=(EditText)findViewById(R.id.editText_number);
        email=(EditText)findViewById(R.id.editText_email);

        editText_id_search.setVisibility(View.GONE);
        button_show_id_result.setVisibility(View.GONE);

        button_clear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                DatabaseHelper db = new DatabaseHelper(getApplicationContext());
                db.clear();
            }
        });



        button_search.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
/*
*/
                editText_id_search.setVisibility(View.VISIBLE);
                button_show_id_result.setVisibility(View.VISIBLE);

                button_show_id_result.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        String  qry = editText_id_search.getText().toString();
                        DatabaseHelper db = new DatabaseHelper(getApplicationContext());
                        db.search(qry);
                    }
                });
            }
        });
        button_submit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                firstnameString = firstName.getText().toString();
                lastnameString=lastName.getText().toString();
                num=number.getText().toString();
                emailString=email.getText().toString();

                DatabaseHelper db = new DatabaseHelper(getApplicationContext());
                db.insertData(firstnameString,lastnameString,num,emailString);
                Toast.makeText(MainActivity.this,"Record Updated",Toast.LENGTH_LONG).show();
                InputMethodManager input = (InputMethodManager) getSystemService(INPUT_METHOD_SERVICE);
                input.hideSoftInputFromWindow(email.getWindowToken(),0);
                firstName.setText("");
                lastName.setText("");
                number.setText("");
                email.setText("");

                db.close();

            }
        });

        button_show_details.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent i = new Intent(MainActivity.this,List_Result.class);

                startActivity(i);
            }
        });


    }



    public void show(String string, String cString, String s, String string1) {

        firstName.setText(string);
        lastName.setText(cString);
        number.setText(s);
        email.setText(string1);
    }
}

DatabaseHelper.java

package com.example.ashish.project;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import java.util.ArrayList;

/**
 * Created by ashis on 7/21/2016.
 */
public class DatabaseHelper extends SQLiteOpenHelper {

    private static int DATABASE_VERSION = 6;
    private static String DATABSE_NAME="DATA";
    private static String TABLE_NAME="PERSONAL_INFORMATION";
    private static String COLLUMN_ID= "_ID";
    private static String COLLUMN_FIRST_NAME="FIRST_NAME";
    private static String COLLUMN_LAST_NAME="LAST_NAME";
    private static String COLLUMN_NUMBER = "NUMBER";
    private static String COLLUMN_EMAIL="EMAIL";

    public DatabaseHelper(Context context)
    {
        super(context,DATABSE_NAME,null,DATABASE_VERSION);

    }


    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {

        String CREATE_TABLE = "CREATE TABLE "+TABLE_NAME + "( "
                                + COLLUMN_ID +" INTEGER PRIMARY KEY, "
                                + COLLUMN_FIRST_NAME + " TEXT, "
                                + COLLUMN_LAST_NAME + " TEXT, "
                                + COLLUMN_NUMBER + " TEXT , "
                                + COLLUMN_EMAIL + " TEXT"+" )";
        sqLiteDatabase.execSQL(CREATE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

        sqLiteDatabase.execSQL("DROP TABLE IF EXISTS"+TABLE_NAME);
        this.onCreate(sqLiteDatabase);

    }


    public void insertData(String firstnameString, String lastnameString, String num, String emailString) {

        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COLLUMN_FIRST_NAME,firstnameString);
        values.put(COLLUMN_LAST_NAME,lastnameString);
        values.put(COLLUMN_NUMBER,num);
        values.put(COLLUMN_EMAIL,emailString);
        db.insertOrThrow(TABLE_NAME,null,values);
        db.close();
    }

    public ArrayList<String> readData() {

        ArrayList<String> list = new ArrayList<>();
        String readQry = "SELECT * FROM "+TABLE_NAME;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor c = db.rawQuery(readQry,null);
        if (c.moveToFirst())
        {
            do {
                list.add(c.getString(0)+ ": "+c.getString(1) +" "+ c.getString(2)+","+c.getString(3)+","+c.getString(4));


            }while (c.moveToNext());

        }
        c.close();
        db.close();



        return list;

    }

    public void clear() {
        SQLiteDatabase db= this.getWritableDatabase();
        String clrqry = "DROP TABLE " + TABLE_NAME;
        db.execSQL(clrqry);

        this.onCreate(db);

    }

    public void search(String srch) {

        SQLiteDatabase db = this.getReadableDatabase();
        MainActivity obj = new MainActivity();
        String sqlqry = "SELECT * FROM "+TABLE_NAME +"  WHERE  "+ COLLUMN_ID + " = ?";
        Cursor c=    db.rawQuery(sqlqry,new  String[]{srch});
        if (c.moveToFirst())
        {
            do {

                        obj.show(c.getString(1),c.getString(2),c.getString(3),c.getString(4));
            }
            while (c.moveToNext());
        }

    }
}

Activity_list.xml

<?xml version="1.0" encoding="utf-8"?>
<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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.ashish.project.List_Result">

    <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/listView2"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:background="@android:color/darker_gray" />
</RelativeLayout>

Activity_list.java

package com.example.ashish.project;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;

public class List_Result extends AppCompatActivity {

    ListView listview1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list__result);
        listview1=(ListView) findViewById(R.id.listView2);


        loadlistviewData();
    }

    private void loadlistviewData() {


        DatabaseHelper db = new DatabaseHelper(getApplicationContext());
        ArrayList<String> list = db.readData();
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getApplicationContext(),android.R.layout.simple_list_item_1,list);
        adapter.setDropDownViewResource(android.R.layout.simple_list_item_1);
        listview1.setAdapter(adapter);

    }
}

这是我输入id

后点击搜索时的logcat

07-25 14:27:34.033 668-668/com.example.ashish.project W/System: ClassLoader referenced unknown path: /data/app/com.example.ashish.project-2/lib/arm
07-25 14:27:34.256 668-668/com.example.ashish.project W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
07-25 14:27:34.541 668-668/com.example.ashish.project D/android.widget.GridLayout: vertical constraints: y4-y0>=864, y4-y3<=192, y3-y2<=91, y2-y1<=91, y1-y0<=100 are inconsistent; permanently removing: y4-y3<=192. 
07-25 14:27:39.235 668-668/com.example.ashish.project D/AndroidRuntime: Shutting down VM
07-25 14:27:39.236 668-668/com.example.ashish.project E/AndroidRuntime: FATAL EXCEPTION: main
                                                                        Process: com.example.ashish.project, PID: 668
                                                                        java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.setText(java.lang.CharSequence)' on a null object reference
                                                                            at com.example.ashish.project.MainActivity.show(MainActivity.java:103)
                                                                            at com.example.ashish.project.DatabaseHelper.search(DatabaseHelper.java:108)
                                                                            at com.example.ashish.project.MainActivity$2$1.onClick(MainActivity.java:60)
                                                                            at android.view.View.performClick(View.java:5201)
                                                                            at android.view.View$PerformClick.run(View.java:21163)
                                                                            at android.os.Handler.handleCallback(Handler.java:746)
                                                                            at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                            at android.os.Looper.loop(Looper.java:148)
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5443)
                                                                            at java.lang.reflect.Method.invoke(Native Method)
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)

任何帮助将不胜感激

Answer 1

您可以通过创建新的MainActivity实例来调用 show（）。因此，MainActivity的所有变量都将为null。最好你应该使这些静态，以便所有MainActivity实例的初始化相同。尝试

static EditText firstName,lastName,number,email,editText_id_search;

Answer 2

不要在View小部件中使用静态。

将DatabaseHelper.java中的搜索功能替换为下面的一个：

public void search(String srch, MainActivity activity) {

    SQLiteDatabase db = this.getReadableDatabase();
    String sqlqry = "SELECT * FROM "+TABLE_NAME +"  WHERE  "+ COLLUMN_ID + " = ?";
    Cursor c=    db.rawQuery(sqlqry,new  String[]{srch});
    if (c.moveToFirst())
    {
        do {

                    activity.show(c.getString(1),c.getString(2),c.getString(3),c.getString(4));
        }
        while (c.moveToNext());
    }

}

在MainActivity.java中，替换如下：

db.search(qry);

使用：

db.search(qry, MainActivity.this);

Answer 3

只需尝试包装即可解决问题。

尝试在空对象引用上调用虚方法'void android.widget.EditText.setText（java.lang.CharSequence）'

3 个答案: