我是Android编程的初学者,要学习它,我自己使用网络上的引用制作了一个示例计算器示例,现在我想这样做。我遵循了Google官方文档中提供的教程“ Building you First App”,并且成功启动了一个使用Intents类按下按钮的新活动,这是应用程序开始时的图像-:
但是当我按下回车按钮时,即使我为新活动设置了android:background选项,也没有将背景设置为该图像,我唯一得到的是空白活动,这是图像-:
这是我的MainActivity的代码,该代码在应用程序启动时启动-
<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>
这是第二个活动的代码,该活动在我按下Enter键时开始,并且使用Intents-完成:
<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>
上方没有显示背景,也没有视图添加到屏幕,这也是我在MainActivity类中使用Intent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;
}
}
}
最佳答案
您需要为您的活动设置内容视图。它已经在示例应用程序活动中完成,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内容视图。
因此,您也需要在super.onCreate(savedInstanceState);
下对CalculatorActivity1执行此操作
您可以在res / layout文件夹中找到第二个布局名称。