MainActivity.java

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.android.explicitintent;

import android.content.Context;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    /* Fields that will store our EditText and Button */
    private EditText mNameEntry;
    private Button mDoSomethingCoolButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        /*
         * Using findViewById, we get a reference to our Button from xml. This allows us to
         * do things like set the onClickListener which determines what happens when the button
         * is clicked.
         */
        mDoSomethingCoolButton = (Button) findViewById(R.id.b_do_something_cool);
        mNameEntry = (EditText) findViewById(R.id.et_text_entry);

        /* Setting an OnClickListener allows us to do something when this button is clicked. */
        mDoSomethingCoolButton.setOnClickListener(new OnClickListener() {

            /**
             * The onClick method is triggered when this button (mDoSomethingCoolButton) is clicked.
             *
             * @param v The view that is clicked. In this case, it's mDoSomethingCoolButton.
             */
            @Override
            public void onClick(View v) {
                // COMPLETED (1) Retrieve the text from the EditText and store it in a variable
                /* We'll first get the text entered by the user in the EditText */
                String textEntered = mNameEntry.getText().toString();

                /*
                 * Storing the Context in a variable in this case is redundant since we could have
                 * just used "this" or "MainActivity.this" in the method call below. However, we
                 * wanted to demonstrate what parameter we were using "MainActivity.this" for as
                 * clear as possible.
                 */
                Context context = MainActivity.this;

                /* This is the class that we want to start (and open) when the button is clicked. */
                Class destinationActivity = ChildActivity.class;

                /*
                 * Here, we create the Intent that will start the Activity we specified above in
                 * the destinationActivity variable. The constructor for an Intent also requires a
                 * context, which we stored in the variable named "context".
                 */
                Intent startChildActivityIntent = new Intent(context, destinationActivity);

                // COMPLETED (2) Use the putExtra method to put the String from the EditText in the Intent
                /*
                 * We use the putExtra method of the Intent class to pass some extra stuff to the
                 * Activity that we are starting. Generally, this data is quite simple, such as
                 * a String or a number. However, there are ways to pass more complex objects.
                 */
                startChildActivityIntent.putExtra(Intent.EXTRA_TEXT, textEntered);

                /*
                 * Once the Intent has been created, we can use Activity's method, "startActivity"
                 * to start the ChildActivity.
                 */
                startActivity(startChildActivityIntent);
            }
        });
    }
}