java.lang.RuntimeException：无法实例化活动ComponentInfo
如何解决这个问题？您需要提供什么？还有什么寻找错误？ Android Studio不会在代码中显示错误
如何解决这个问题？您需要提供什么？还有什么寻找错误？ Android Studio不会在代码中显示错误
MainActivity.java：
package shabunin.da;
import android.content.Intent;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;
import java.io.IOException;
public class MainActivity extends AppCompatActivity {
private DBHandler dbHandler;
private SQLiteDatabase database;
TextView textView = (TextView) findViewById(R.id.textView);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Thread mainThread = Thread.currentThread();
Toast.makeText(getApplicationContext(), "Текущий поток " + mainThread.getName(), Toast.LENGTH_LONG).show();
dbHandler = new DBHandler(this);
try {
dbHandler.updateDataBase();
} catch (IOException mIOException) {
throw new Error("Error #1: can't connect to DataBase");
}
try {
database = dbHandler.getWritableDatabase();
} catch (SQLException mSQLException) {
throw mSQLException;
}
}
public void onClick(View view){
switch(view.getId()){
case R.id.pathToRegistrationText:
Toast.makeText(getApplicationContext(), "Вы перешли на другую активити", Toast.LENGTH_LONG).show();
Intent intentRegistration = new Intent(MainActivity.this, RegistrationActivity.class);
startActivity(intentRegistration);
break;
case R.id.pathToForgotPassword:
Toast.makeText(getApplicationContext(), "Вы перешли на другую активитиs", Toast.LENGTH_LONG).show();
Intent intentForgot = new Intent(MainActivity.this, ForgotActivity.class);
startActivity(intentForgot);
break;
case R.id.enterButton:
String product = "";
Cursor cursor = database.rawQuery("SELECT * FROM clients", null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
product += cursor.getString(1) + " | ";
cursor.moveToNext();
}
cursor.close();
textView.setText(product);
break;
}
}
}
DBHandler.java：
package shabunin.da;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
public class DBHandler extends SQLiteOpenHelper {
private static String DB_NAME = "freelance.db";
private static String DB_PATH = "";
private static final int DB_VERSION = 2;
private SQLiteDatabase mDataBase;
private final Context mContext;
private boolean mNeedUpdate = false;
public DBHandler(Context context) {
super(context, DB_NAME, null, DB_VERSION);
if (android.os.Build.VERSION.SDK_INT >= 17)
DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
else
DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
this.mContext = context;
copyDataBase();
this.getReadableDatabase();
}
public void updateDataBase() throws IOException {
if (mNeedUpdate) {
File dbFile = new File(DB_PATH + DB_NAME);
if (dbFile.exists())
dbFile.delete();
copyDataBase();
mNeedUpdate = false;
}
}
private boolean checkDataBase() {
File dbFile = new File(DB_PATH + DB_NAME);
return dbFile.exists();
}
private void copyDataBase() {
if (!checkDataBase()) {
this.getReadableDatabase();
this.close();
try {
copyDBFile();
} catch (IOException mIOException) {
throw new Error("ErrorCopyingDataBase");
}
}
}
private void copyDBFile() throws IOException {
InputStream mInput = mContext.getAssets().open(DB_NAME);
//InputStream mInput = mContext.getResources().openRawResource(R.raw.info);
OutputStream mOutput = new FileOutputStream(DB_PATH + DB_NAME);
byte[] mBuffer = new byte[1024];
int mLength;
while ((mLength = mInput.read(mBuffer)) > 0)
mOutput.write(mBuffer, 0, mLength);
mOutput.flush();
mOutput.close();
mInput.close();
}
public boolean openDataBase() throws SQLException {
mDataBase = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.CREATE_IF_NECESSARY);
return mDataBase != null;
}
@Override
public synchronized void close() {
if (mDataBase != null)
mDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (newVersion > oldVersion)
mNeedUpdate = true;
}
}
MainActivity.xml：
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<ImageView
android:id="@+id/imageView"
android:layout_width="217dp"
android:layout_height="121dp"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginTop="60dp"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:srcCompat="@drawable/wave" />
<EditText
android:id="@+id/loginNameText"
android:layout_width="300dp"
android:layout_height="75dp"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginTop="60dp"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:backgroundTint="@color/colorBrand"
android:ems="10"
android:hint="Логин"
android:imeOptions="actionDone"
android:maxLength="24"
android:singleLine="true"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.505"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/imageView" />
<EditText
android:id="@+id/loginPasswordText"
android:layout_width="300dp"
android:layout_height="75dp"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:backgroundTint="@color/colorBrand"
android:ems="10"
android:hint="Пароль"
android:imeOptions="actionDone"
android:inputType="textPassword"
android:maxLength="24"
android:singleLine="true"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/loginNameText" />
<Button
android:id="@+id/enterButton"
android:layout_width="300dp"
android:layout_height="50dp"
android:layout_marginLeft="25dp"
android:layout_marginTop="60dp"
android:layout_marginRight="25dp"
android:background="@color/colorBrand"
android:text="Войти"
android:textColor="@color/colorWhite"
app:layout_constraintHorizontal_bias="0.508"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@+id/loginPasswordText" />
<TextView
android:id="@+id/noteToRegistrationText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="60dp"
android:text="У вас нет аккаунта?"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@+id/enterButton" />
<TextView
android:id="@+id/pathToRegistrationText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:clickable="true"
android:onClick="onClick"
android:text="Зарегистрируйтесь"
android:textColor="@color/colorBrand"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/noteToRegistrationText" />
<TextView
android:id="@+id/pathToForgotPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
android:layout_marginBottom="8dp"
android:clickable="true"
android:onClick="onClick"
android:text="Забыли пароль?"
android:textColor="@color/colorBrand"
app:layout_constraintBottom_toTopOf="@+id/enterButton"
app:layout_constraintEnd_toEndOf="@+id/enterButton"
app:layout_constraintTop_toBottomOf="@+id/loginPasswordText"
app:layout_constraintVertical_bias="0.0" />
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginLeft="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"
android:text="TextView"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/pathToRegistrationText" />
</android.support.constraint.ConstraintLayout>
错误：
I/InstantRun: starting instant run server: is main process
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: shabunin.da, PID: 27003
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{shabunin.da/shabunin.da.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2843)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.support.v7.app.AppCompatDelegateImpl.<init>(AppCompatDelegateImpl.java:249)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:182)
at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:520)
at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:191)
at shabunin.da.MainActivity.<init>(MainActivity.java:19)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:69)
at android.support.v4.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:43)
at android.app.Instrumentation.newActivity(Instrumentation.java:1215)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2831)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)