编译时的Android MySQLite问题

Question

Im progressing with creating a simple database for a project at school, however the code itself shows no errors, but when i run the project in an emulator, it spits out an error. I Think the problem is stemming from the AlertDialog, but im not sure whats wrong with the syntax Here is a copy of my code..

package com.example.bash1.sqlitediss;

import android.app.AlertDialog; 
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar; 
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.view.View.OnClickListener;

public class MainActivity extends AppCompatActivity {

DatabaseHelper myDb;
private Button button3;
Button buttonviewall;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    myDb = new DatabaseHelper(this);
    buttonviewall = (Button) findViewById(R.id.button3);
    viewAll();

}
{

    Button button = (Button) findViewById(R.id.button);
    button.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent1 = new Intent(MainActivity.this, DatabaseActivity.class);
            startActivity(intent1);
        }
    });
    {
    }

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
}

public void viewAll() {
    buttonviewall.setOnClickListener(
            new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    Cursor res = myDb.getAllData();
                    if (res.getCount() == 0)
                    // show message
                    {
                        showMessage("Error", "Nothing found");
                        return;
                    }

                    StringBuffer buffer = new StringBuffer();
                    while (res.moveToNext()) {
                        buffer.append("ID :" + res.getString(0) + "\n");
                        buffer.append("Name :" + res.getString(1) + "\n");
                        buffer.append("Datereceived :" + res.getString(2) + "\n");
                        buffer.append("Expirydate :" + res.getString(3) + "\n\n");
                    }
                    // Show all data
                    showMessage("Data", buffer.toString());

                }
            }

    );
}


public void showMessage(String title, String Message) {
      AlertDialog.Builder builder = new AlertDialog.Builder(this);
      builder.setCancelable(true);
      builder.setTitle(title);
      builder.setMessage(Message);
      builder.show();

    builder.show();
}



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

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

}

Activitymain.xml

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

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<include layout="@layout/content_main" />

<android.support.design.widget.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    android:src="@android:drawable/ic_dialog_email" />

Error message log:

04-20 06:40:57.114 17890-17890/com.example.bash1.sqlitediss E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: com.example.bash1.sqlitediss, PID: 17890
                                                                          java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.bash1.sqlitediss/com.example.bash1.sqlitediss.MainActivity}: java.lang.NullPointerException
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:135)
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                              at android.os.Looper.loop(Looper.java:136)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5001)
                                                                              at java.lang.reflect.Method.invokeNative(Native Method)
                                                                              at java.lang.reflect.Method.invoke(Method.java:515)
                                                                              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
                                                                              at dalvik.system.NativeStart.main(Native Method)
                                                                           Caused by: java.lang.NullPointerException
                                                                              at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:68)
                                                                              at android.support.v7.app.AppCompatDelegateImplV7.<init>(AppCompatDelegateImplV7.java:145)
                                                                              at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:28)
                                                                              at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:41)
                                                                              at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:188)
                                                                              at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:170)
                                                                              at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:502)
                                                                              at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:174)
                                                                              at com.example.bash1.sqlitediss.MainActivity.<init>(MainActivity.java:35)
                                                                              at java.lang.Class.newInstanceImpl(Native Method)
                                                                              at java.lang.Class.newInstance(Class.java:1208)
                                                                              at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2101)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233) 
                                                                              at android.app.ActivityThread.access$800(ActivityThread.java:135) 
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                              at android.os.Looper.loop(Looper.java:136) 
                                                                              at android.app.ActivityThread.main(ActivityThread.java:5001) 
                                                                              at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                              at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
                                                                              at dalvik.system.NativeStart.main(Native Method) 

Answer 1

You have a NullPointerException at lines: 2184, 2233, 135, 1196, 102. Can you comment those lines under this answer. So I can take a look at them and see what is going on.

Answer 2

Your stacktrace has the "caused by" exception below the RuntimeException wrapper you have posted with specific details.

Anyway, one certain way your code can cause an NPE is that buttonviewall is not initialized before you're calling ViewAll() which calls a method on buttonviewall .

---

After edited question:

Remove the

}
{

The first } ends the onCreate() method and the second { starts a new initializer block that is executed at instance initialization phase. You need to execute that code as part of onCreate() as <init> is too early for eg findViewById() .