Android上的操作Android不起作用

Question

我一直在努力讓用戶在菜單上點擊後改變背景顏色，但我不明白爲什麼它不起作用。我沒有任何警告或錯誤！

我activity_main.xml中：

<RelativeLayout 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:id="@+id/utilayout" 
tools:context=".MainActivity" 
> 

<TextView 
    android:id="@+id/hello1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="@string/hello_world" /> 

<ImageView 
    android:id="@+id/imageView1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below="@+id/hello1" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="80dp" 
    android:src="@drawable/ic_launcher" android:contentDescription="@string/hello_world"/> 

我MainActivity.java：

package com.example.menu; 
import android.os.Bundle; 
import android.app.Activity; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.widget.RelativeLayout; 
import android.widget.TextView; 


public class MainActivity extends Activity { 

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


@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; 
} 

public boolean onOptionsItemsSelected(MenuItem item) 
{ 
    RelativeLayout bkgr = (RelativeLayout) findViewById(R.id.utilayout); 

    switch(item.getItemId()) 
    { 
    case R.id.action_black: 
     bkgr.setBackgroundResource(R.color.black); 
     return true; 

    case R.id.action_red: 
     bkgr.setBackgroundResource(R.color.red); 
     return true; 

    case R.id.action_hello: 
     TextView tv = (TextView) findViewById(R.id.hello1); 
     tv.setText("What up people?"); 
     return true; 

    default: return super.onOptionsItemSelected(item); 
    } 
} 
} 

的main.xml（菜單）

<menu xmlns:android="http://schemas.android.com/apk/res/android" > 


    <item 
    android:id="@+id/action_red" 
    android:orderInCategory="100" 
    android:showAsAction="never" 
    android:title="@string/action_red"/> 
    <item 
    android:id="@+id/action_black" 
    android:orderInCategory="200" 
    android:showAsAction="never" 
    android:title="@string/action_black"/> 
    <item 
    android:id="@+id/action_hello" 
    android:orderInCategory="300" 
    android:showAsAction="never" 
    android:title="@string/hello"/> 

Answer 1

與您現有的一個替換此代碼。和你的應用程序將運行良好

MainActivity.java：

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    RelativeLayout bkgr = (RelativeLayout) findViewById(R.id.utilayout); 
    switch (item.getItemId()) { 
     case R.id.action_black: 
      bkgr.setBackgroundResource(R.color.black); 
      return true; 
     case R.id.action_red: 
      bkgr.setBackgroundResource(R.color.red); 
      return true; 
     case R.id.action_hello: 
      TextView tv = (TextView) findViewById(R.id.hello1); 
      tv.setText("What up people?"); 
      return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 

的main.xml（菜單）

<item 
     android:id="@+id/action_red" 
     android:orderInCategory="100" 
     android:showAsAction="always" 
     android:title="red action"/> 
<item 
     android:id="@+id/action_black" 
     android:orderInCategory="200" 
     android:showAsAction="always" 
     android:title="black action"/> 
<item 
     android:id="@+id/action_hello" 
     android:orderInCategory="300" 
     android:showAsAction="always" 
     android:title="hello"/> 
</menu> 

Answer 2

更改 '迴歸真實' 到 '休息'
編輯：

switch(item.getItemId()) 
{ 
    case R.id.action_black: 
    bkgr.setBackgroundResource(R.color.black); 
    break; 

case R.id.action_red: 
    bkgr.setBackgroundResource(R.color.red); 
    break; 

case R.id.action_hello: 
    TextView tv = (TextView) findViewById(R.id.hello1); 
    tv.setText("What up people?"); 
    break; 

default: 
break; 
return super.onOptionsItemSelected(item); 
}