我需要一些3个无法正常使用的按钮来解决问题，我不确定如何解决。 “保存”按钮用于保存我的数据库，“刷新”按钮用于清除，“搜索”按钮用于查找现有数据库。我的TextView显示注册后的现有数据库。这些是我要实现的目标。
这是我的代码文件：
XML文件： activity_main：
<?xml version="1.0" encoding="utf-8"?>
<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:tools="http://schemas.android.com/tools"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_verticsl_margin"
android:paddingBottom="@dimen/activity_verticsl_margin"
tools:context=".MainActivity">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="30dip"
android:gravity="center"
android:text="Registration"/>
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:weightSum="1">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/txtid"
android:hint="ID"
android:inputType="number"
android:layout_marginTop="5dip"
/>
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/txtfirstname"
android:hint="@string/first_name"
android:layout_marginTop="5dip"
/>
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/txtlastname"
android:hint="@string/last_name"
android:layout_marginTop="5dip"
/>
<EditText
android:id="@+id/txtmail"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="5dip"
android:hint="@string/e_mail" />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/txtuser"
android:hint="@string/username"
android:layout_marginTop="5dip"/>
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/txtpw"
android:hint="@string/password"
android:layout_marginTop="5dip"/>
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="save"
android:textColor="#fff"
android:textSize="15dip"
android:id="@+id/btnsave"
android:layout_weight="1"
android:layout_gravity="center_horizontal"/>
<Button
android:id="@+id/btnclear"
android:layout_width="212dp"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_weight=".30"
android:text="refresh"
android:textColor="#fff"
android:textSize="15dip"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="search"
android:textColor="#fff"
android:textSize="15dip"
android:id="@+id/btnsearch"
android:layout_weight="1"
android:layout_gravity="center_horizontal"/>
</LinearLayout>
</LinearLayout>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="New Text"
android:id="@+id/textView"/>
</TableLayout>
Java文件StudentRegistration.java：
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class StudentRegistration {
public static final String KEY_ROWID ="_id";
public static final String KEY_FNAME = "fname";
public static final String KEY_LNAME = "lname";
public static final String KEY_EMAIL = "email";
public static final String KEY_USER ="user";
public static final String KEY_PASS ="pass";
private static final String DATABASE_NAME = "StudentDB";
private static final String DATABASE_TABLE = "StudentTbl";
private static final int DATABASE_VERSION = 1;
private DBHelper ourHelper;
private final Context ourContext;
private SQLiteDatabase ourDatabase;
private static class DBHelper extends SQLiteOpenHelper {
public DBHelper(Context context) {
super(context, DATABASE_NAME,
null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE " + DATABASE_TABLE + " (" +
KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
KEY_FNAME + " TEXT NOT NULL, " +
KEY_LNAME + " TEXT NOT NULL, " +
KEY_EMAIL + " TEXT NOT NULL, " +
KEY_USER + " TEXT NOT NULL, " +
KEY_PASS + " TEXT NOT NULL);");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_NAME);
onCreate(db);
}
}
public StudentRegistration(Context c) {
ourContext = c;
}
public StudentRegistration open() {
ourHelper = new DBHelper(ourContext);
ourDatabase = ourHelper.getWritableDatabase();
return this;
}
public void close() {
ourHelper.close();
}
public long savedata(String fname, String lname, String email, String user, String pass) {
ContentValues cv = new ContentValues();
cv.put(KEY_FNAME, fname);
cv.put(KEY_LNAME, lname);
cv.put(KEY_EMAIL, email);
cv.put(KEY_USER, user);
cv.put(KEY_PASS, pass);
return ourDatabase.insert(DATABASE_TABLE, null, cv);
}
public String getData(){
String[] refresh = new String[] {KEY_ROWID, KEY_FNAME, KEY_LNAME, KEY_EMAIL, KEY_USER, KEY_PASS};
Cursor c = ourDatabase.query(DATABASE_TABLE, refresh, null, null, null, null, null);
String result = "";
int iRow = c.getColumnIndex(KEY_ROWID);
int iFName = c.getColumnIndex(KEY_FNAME);
int iLName = c.getColumnIndex(KEY_LNAME);
int iEmail = c.getColumnIndex(KEY_EMAIL);
int iUser = c.getColumnIndex(KEY_USER);
int iPass = c.getColumnIndex(KEY_PASS);
for(c.moveToFirst(); !c.isAfterLast();c.moveToNext()){
result = result + c.getString(iRow)
+ " " + c.getString(iFName)
+ " " + c.getString(iLName)
+ " " + c.getString(iEmail)
+ " " + c.getString(iUser)
+ " " + c.getString(iPass)
+ "\n\n";
}
return result;
}
public String getFName(long l){
String[] getfname = new String[] {KEY_ROWID, KEY_FNAME, KEY_LNAME,
KEY_EMAIL, KEY_USER, KEY_PASS};
Cursor c = ourDatabase.query(DATABASE_TABLE, getfname, KEY_ROWID + "="
+ 1, null, null, null, null);
if(c != null){
c.moveToFirst();
String fname = c.getString(1);
return fname;
}
return null;
}
public String getLName(long l){
String[] getlname = new String[] {KEY_ROWID, KEY_FNAME, KEY_LNAME,
KEY_EMAIL, KEY_USER, KEY_PASS};
Cursor c = ourDatabase.query(DATABASE_TABLE, getlname, KEY_ROWID + "="
+ 1, null, null, null, null);
if(c != null){
c.moveToFirst();
String lname = c.getString(2);
return lname;
}
return null;
}
public String getEmail(long l){
String[] getemail = new String[] {KEY_ROWID, KEY_FNAME, KEY_LNAME,
KEY_EMAIL, KEY_USER, KEY_PASS};
Cursor c = ourDatabase.query(DATABASE_TABLE, getemail, KEY_ROWID + "="
+ 1, null, null, null, null);
if(c != null){
c.moveToFirst();
String email = c.getString(3);
return email;
}
return null;
}
public String getUser(long l){
String[] getuser = new String[] {KEY_ROWID, KEY_FNAME, KEY_LNAME,
KEY_EMAIL, KEY_USER, KEY_PASS};
Cursor c = ourDatabase.query(DATABASE_TABLE, getuser, KEY_ROWID + "="
+ 1, null, null, null, null);
if(c != null){
c.moveToFirst();
String user = c.getString(4);
return user;
}
return null;
}
public String getPass(long l){
String[] getpass = new String[] {KEY_ROWID, KEY_FNAME, KEY_LNAME,
KEY_EMAIL, KEY_USER, KEY_PASS};
Cursor c = ourDatabase.query(DATABASE_TABLE, getpass, KEY_ROWID + "="
+ 1, null, null, null, null);
if(c != null){
c.moveToFirst();
String pass = c.getString(5);
return pass;
}
return null;
}
}
和Java文件MainActivity：
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
EditText FirstName, LastName, Email, UserName, Password, ID;
Button Save, Clear, Search;
TextView TxtData;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FirstName = (EditText)findViewById(R.id.txtfirstname);
LastName = (EditText)findViewById(R.id.txtlastname);
Email = (EditText)findViewById(R.id.txtmail);
UserName = (EditText)findViewById(R.id.txtuser);
Password = (EditText)findViewById(R.id.txtpw);
TxtData =(TextView)findViewById(R.id.textView);
Save =(Button)findViewById(R.id.btnsave);
Clear=(Button)findViewById(R.id.btnclear);
Search=(Button)findViewById(R.id.btnsearch);
Search.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
String search = ID.getText().toString();
Long l= Long.parseLong(search);
StudentRegistration mysearch = new
StudentRegistration(MainActivity.this);
mysearch.open();
String returnedFname = mysearch.getFName(l);
String returnedLname = mysearch.getLName(l);
String returnedEmail = mysearch.getEmail(l);
String returnedUser = mysearch.getUser(l);
String returnedPass = mysearch.getPass(l);
mysearch.close();
FirstName.setText(returnedFname);
LastName.setText(returnedLname);
Email.setText(returnedEmail);
UserName.setText(returnedUser);
Password.setText(returnedPass);
}
});
Save.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String fname = FirstName.getText().toString();
String lname = LastName.getText().toString();
String email = Email.getText().toString();
String user = UserName.getText().toString();
String pass = Password.getText().toString();
StudentRegistration save = new StudentRegistration(MainActivity.this);
save.open();
save.savedata(fname, lname, email, user, pass);
FirstName.setText("");
LastName.setText("");
Email.setText("");
UserName.setText("");
Password.setText("");
ID.setText("");
}
});
Clear.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v){
StudentRegistration refresh = new StudentRegistration(MainActivity.this);
refresh.open();
String data = refresh.getData();
refresh.close();
TxtData.setText(data);
FirstName.setText("");
LastName.setText("");
Email.setText("");
UserName.setText("");
Password.setText("");
ID.setText("");
}
});
}
}
我的清单文件：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.classifiedinformation">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
我如何实现我的目标？
答案 0 :(得分：0)
首先，关于发生问题的一些提示会很好。
您需要像使用其他EditText一样初始化ID。
将ID = findViewById(R.id.txtid);添加到您的onCreate(Bundle savedInstanceState)方法中。
点击“保存”时，我得到的第一件事是：
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.setText(java.lang.CharSequence)' on a null object reference
at com.citiesapps.myapplication.MainActivity$2.onClick(MainActivity.java:76)
at android.view.View.performClick(View.java:5610)
at android.view.View$PerformClick.run(View.java:22265)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
作为stacktrace的状态，您试图在这种情况下的“ ID”上调用空对象上的方法。
答案 1 :(得分：0)
分析您的代码后，我看到您正在对未在Java类中初始化的editText执行 setText 。
可能的editText代码为：
ID.setText("");此处的ID未使用xml文件初始化。
使用ID = findViewById(R.id.txtid);初始化ID字段
检查所有editText初始化。然后使用该editText。
谢谢：）