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Im在學校爲一個項目創建一個簡單的數據庫，但是代碼本身沒有顯示錯誤，但是當我在模擬器中運行該項目時，它吐出了一個錯誤。 我認爲這個問題是從AlertDialog而產生，但林不知道什麼是錯的語法 這裏是我的代碼的副本..編譯時出現的Android MySQLite問題
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" />
錯誤消息日誌：
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)
添加AndroidManifest.xml中的所有活動 –
你能說出'DatabaseActivity'的擴展嗎？ –
DatabaseActivity是一個獨立的類 –