android - 如何从主要 Activity 开始新 Activity 并显示所有元素以及背景？

Question

我是 Android 编程的初学者，为了学习它，我正在使用网络上的引用资料自己制作一个示例计算器示例，现在这是我想做的事情。我遵循了 Google 官方文档中提供的教程“构建您的第一个应用程序”，并且成功地引发了使用 Intents 类点击按钮的新 Activity ，这是该应用程序的图像开始 -:

但是当我按下回车按钮时，即使我为新 Activity 设置了 android:background 选项，它也没有将背景设置为该图像，我唯一得到的是一个空白 Activity ，这是图像-:

这是在应用程序启动时启动的 MainActivity 的代码 -

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="@drawable/math_symbols" >

    <Button android:id="@+id/enter_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/enter_button"
            android:onClick="enterCalculator"/>
</LinearLayout>

这是第二个 Activity 的代码，当我按下回车按钮时开始，这是使用 Intents 完成的:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" 
    android:orientation="vertical" 
    android:background="@drawable/calculato_activity_1" >

     <RadioGroup android:id="@+id/operation_radio_group"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="30dip"
            android:orientation="horizontal">

        <RadioButton android:id="@+id/sum"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
                 android:text="@string/sum">

        </RadioButton>

        <RadioButton android:id="@+id/difference"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
                 android:text="@string/difference">

        </RadioButton>

        <RadioButton android:id="@+id/multiply"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
                 android:text="@string/multiply">

        </RadioButton>

    </RadioGroup>
</LinearLayout>

上面没有显示背景，也没有向屏幕添加 View ，这也是我在 MainActivity 类中使​​用 Intents 的方式 -:

package com.example.mathcalculator;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;

public class MainActivity extends ActionBarActivity {

    // this is the message used to enter the main calculator activity
    public static String ENTER_MESSAGE = "com.example.mathcalculator.MainActivity.Message";

    // this method is used to enter the actual calculator screen
    public void enterCalculator(View view){

        // we create an Intent to carry over the data from the button and enter the CalculatorActivity1
        Intent intent = new Intent(this, CalculatorActivity1.class);

        // put the key-value pair into the intent
        intent.putExtra(ENTER_MESSAGE, "ENTER");

        // start the new activity with the intent as the input which carries over the message bundle
        startActivity(intent);
    }

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

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.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();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container,
                    false);
            return rootView;
        }
    }

}

这是 CalculatorActivity1 类的代码 -:

package com.example.mathcalculator;

import android.support.v7.app.ActionBarActivity;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

public class CalculatorActivity1 extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.calculator_activity1, 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();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(
                    R.layout.fragment_calculator_activity1, container, false);
            return rootView;
        }
    }

}

Answer 1

您需要为您的 Activity 设置内容 View 。它已经在示例应用 Activity 中完成，因此在 MainActivity 的 oncreate 方法中，您可以看到:setContentView(R.layout.activity_main);它将 activity_main 布局设置为 MainActivity 内容 View 。因此，您也需要在 super.onCreate(savedInstanceState); 下对 CalculatorActivity1 执行此操作您可以在 res/layout 文件夹中找到您的第二个布局名称。