【发布时间】：2017-08-24 16:18:51
【问题描述】：
我在以编程方式设置背景时遇到问题。我做不到。
这是我的主题课。代码中有应该更改主背景的单选按钮。到目前为止，我已经为两个单选按钮（即 radioButtonMountains 和 radioButtonSea）编写了实现，它们应该加载两个不同的图像（即 mountain.png 和 sea.png）。
public class ThemeActivity extends BasicActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_theme);
ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setTitle("Motywy");
setAction();
}
private void setAction(){
relativeLayout=(RelativeLayout) findViewById(R.id.relativeLayoutid);
radioGroup=(RadioGroup) findViewById(R.id.radioGroup);
radioButtonMountains=(RadioButton) findViewById(R.id.radioMountains);
radioButtonCity=(RadioButton) findViewById(R.id.radioCity);
radioButtonSea=(RadioButton) findViewById(R.id.radioSea);
radioButtonNature=(RadioButton) findViewById(R.id.radioNature);
radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChanged(RadioGroup group, int checkedId) {
if(radioButtonMountains.isChecked()){
//relativeLayout.setBackgroundDrawable(getResources().getDrawable(R.drawable.mountains));
//relativeLayout.setBackground(getResources().getDrawable(R.drawable.mountains));
relativeLayout.setBackgroundResource(R.drawable.mountains);
}
else if(radioButtonCity.isChecked()){
}
else if(radioButtonSea.isChecked()){
relativeLayout.setBackgroundResource(R.drawable.sea);
}
else if(radioButtonNature.isChecked()){
}
}
});
}
这是我的主类的activity_main.xml（如果需要，我可以将代码粘贴到我的主类中）。我添加了上面提到的 'android:id="@+id/relativeLayoutid"'。
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/relativeLayoutid"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/sea"
android:orientation="vertical" >
// other things like a ImageButton, a TextView etc
</RelativeLayout>
最后，当我点击其中一个单选按钮时，替换为：
11-11 21:28:34.172: D/AndroidRuntime(22316): Shutting down VM
11-11 21:28:34.172: W/dalvikvm(22316): threadid=1: thread exiting with uncaught exception (group=0x411162a0)
11-11 21:28:34.202: E/AndroidRuntime(22316): FATAL EXCEPTION: main
11-11 21:28:34.202: E/AndroidRuntime(22316): java.lang.NullPointerException
11-11 21:28:34.202: E/AndroidRuntime(22316): at com.example.runapp.ThemeActivity$1.onCheckedChanged(ThemeActivity.java:43)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.widget.RadioGroup.setCheckedId(RadioGroup.java:174)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.widget.RadioGroup.access$600(RadioGroup.java:54)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.widget.RadioGroup$CheckedStateTracker.onCheckedChanged(RadioGroup.java:358)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.widget.CompoundButton.setChecked(CompoundButton.java:140)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.widget.CompoundButton.toggle(CompoundButton.java:92)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.widget.RadioButton.toggle(RadioButton.java:76)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.widget.CompoundButton.performClick(CompoundButton.java:104)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.view.View$PerformClick.run(View.java:17082)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.os.Handler.handleCallback(Handler.java:615)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.os.Handler.dispatchMessage(Handler.java:92)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.os.Looper.loop(Looper.java:137)
11-11 21:28:34.202: E/AndroidRuntime(22316): at android.app.ActivityThread.main(ActivityThread.java:4867)
11-11 21:28:34.202: E/AndroidRuntime(22316): at java.lang.reflect.Method.invokeNative(Native Method)
11-11 21:28:34.202: E/AndroidRuntime(22316): at java.lang.reflect.Method.invoke(Method.java:511)
11-11 21:28:34.202: E/AndroidRuntime(22316): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
11-11 21:28:34.202: E/AndroidRuntime(22316): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
11-11 21:28:34.202: E/AndroidRuntime(22316): at dalvik.system.NativeStart.main(Native Method)
应用程序已关闭。我试过这样用：
relativeLayout.setBackgroundResource(R.drawable.mountains);
这样：
relativeLayout.setBackground(getResources().getDrawable(R.drawable.mountains));
这样：
relativeLayout.setBackgroundDrawable(getResources().getDrawable(R.drawable.mountains));
它们都不起作用。
我该如何解决这个问题？我应该纠正什么？
解决办法：
- 将 relativeLayout=(RelativeLayout) findViewById(R.id.relativeLayoutid) 和 setBackgroundResource() 方法移到 setContentView() 方法后面的主要活动中。
- 创建一个静态变量，并将该变量作为参数放入 setBackgroundResource() 方法中。
- 在您拥有单选按钮的主题活动中更改静态变量。
MainActivity 类：
@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
public class MainActivity extends BasicActivity implements OnClickListener {
public final static String EXTRA_MESSAGE = "com.example.helloworld.MESSAGE";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//other things
setContentView(R.layout.activity_main);
relativeLayout=(RelativeLayout) findViewById(R.id.relativeLayoutid);
if(image==0) relativeLayout.setBackgroundResource(R.drawable.mountains);
else relativeLayout.setBackgroundResource(image);
//other things
}
//other things
public RelativeLayout relativeLayout;
public static int image;
}
MainActivity 类的activity_main.xml：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/relativeLayoutid"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/sea"
android:orientation="vertical" >
// other things like a ImageButton, a TextView etc
</RelativeLayout>
我更改主背景的 ThemeActivity 类：
public class ThemeActivity extends BasicActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_theme);
ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setTitle("Theme");
setAction();
}
private void setAction(){
radioGroup=(RadioGroup) findViewById(R.id.radioGroup);
radioButtonMountains=(RadioButton) findViewById(R.id.radioMountains);
radioButtonCity=(RadioButton) findViewById(R.id.radioCity);
radioButtonSea=(RadioButton) findViewById(R.id.radioSea);
radioButtonNature=(RadioButton) findViewById(R.id.radioNature);
setRadioChoose();
radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChanged(RadioGroup group, int checkedId) {
if(radioButtonMountains.isChecked()){
MainActivity.image=R.drawable.mountains;
}
else if(radioButtonCity.isChecked()){
MainActivity.image=R.drawable.city;
}
else if(radioButtonSea.isChecked()){
MainActivity.image=R.drawable.sea;
}
else if(radioButtonNature.isChecked()){
MainActivity.image=R.drawable.nature;
}
saveRadioChoose(checkedId);
}
});
}
private void setRadioChoose(){
radioChoose=PreferenceManager.getDefaultSharedPreferences(getBaseContext());
radioChooseEdit=radioChoose.edit();
int radio=radioChoose.getInt("RADIO", 0);
if(radio==radioButtonMountains.getId()) radioButtonMountains.setChecked(true);
else if(radio==radioButtonCity.getId()) radioButtonCity.setChecked(true);
else if(radio==radioButtonSea.getId()) radioButtonSea.setChecked(true);
else if(radio==radioButtonNature.getId()) radioButtonNature.setChecked(true);
else if(radio==0) radioButtonMountains.setChecked(true);
}
private void saveRadioChoose(int checkedId){
radioChooseEdit.putInt("RADIO", checkedId);
radioChooseEdit.commit();
}
private RadioGroup radioGroup;
private RadioButton radioButtonMountains;
private RadioButton radioButtonCity;
private RadioButton radioButtonSea;
private RadioButton radioButtonNature;
private SharedPreferences radioChoose;
private SharedPreferences.Editor radioChooseEdit;
}
【问题讨论】：
-
查看以下 SO 答案... [希望对您有所帮助][1] [1]：stackoverflow.com/questions/12678949/…
-
在 onCheckedChanged() 监听器中粘贴一个调试点，当它被命中时查看所有 RadioButton 对象是否设置正确。
-
你的 ThemeActivity 的第 43 行是什么？
-
@Houcine：在第43行是：relativeLayout.setBackgroundResource(R.drawable.mountains);
-
relativeLayout 变量为空。因为你有一个 NullPointerException。检查 relativeLayout 是否不同于 null 并显示日志，或尝试调试它。在此之前，请清理您的项目。