如何解决 Intent 崩溃？

Question

I'm beginner and don't know why my using Intent to layout makes my program crashed? But I used this code before and it works. Now it is not working. What are the wrong of my code?.

JAVA

import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;


public class Mobile_Grocery_App extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_mobile__grocery__app);
    }
    public void signin(View view) {
        Intent i = new Intent(this, Sign_In.class);
        startActivity(i);
   }

XML

<ImageView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/main_background"
    android:src="@drawable/mobile_grocery"
    android:scaleType="centerCrop"
    />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="MOBILE GROCERY"
    android:id="@+id/mobile_grocery"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:textSize="45dp"
    android:textColor="#000000"
    android:gravity="center"
    />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Application"
    android:id="@+id/application"
    android:textColor="#000000"
    android:textSize="25dp"
    android:layout_below="@+id/mobile_grocery"
    android:layout_centerHorizontal="true" />

<EditText
    android:layout_width="200dp"
    android:layout_height="wrap_content"
    android:id="@+id/username"
    android:layout_alignParentBottom="true"
    android:layout_alignRight="@+id/application"
    android:layout_alignEnd="@+id/application"
    android:layout_marginBottom="128dp"
    android:hint="Username"
    android:textColorHint="#000000"

    />

<EditText
    android:layout_width="200dp"
    android:layout_height="wrap_content"
    android:id="@+id/password"
    android:layout_alignTop="@+id/username"
    android:layout_alignRight="@+id/username"
    android:layout_alignEnd="@+id/username"
    android:layout_marginTop="36dp"
    android:hint="Password"
    android:textColorHint="#000000"
    />

<Button
    style="?android:attr/buttonStyleSmall"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Sign In"
    android:id="@+id/sign_in"
    android:layout_below="@+id/password"
    android:layout_alignLeft="@+id/password"
    android:layout_alignStart="@+id/password"
    android:onClick="signin"
    />

<Button
    style="?android:attr/buttonStyleSmall"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Sign Up"
    android:id="@+id/sign_up"
    android:layout_below="@+id/password"
    android:layout_alignRight="@+id/password"
    android:layout_alignEnd="@+id/password"
    android:onClick="signup"
    />

Hope somebody can help me

Answer 1

The issue is due to android:onClick="signup" . Everytime you declare the android:onclick property in one of the widgets in your xml, Android expects to find a method with the following signature

public void nameOfTheProperty(View view) {

}

in your case you declared public void signin(View view) , but you are still missing

public void signup(View view) {

}

Answer 2

Try doing this:

 public void signin(View view) {
            Intent i = new Intent(Mobile_Grocery_App.this, Sign_In.class);
            startActivity(i);
       }