Java 异常设置背景色
我对我的代码有一个问题,它应该更改我开始活动的背景色。我应该用单选按钮(在RadioGroup中)在蓝色和红色之间进行选择。当我点击设置菜单中的红色/蓝色单选按钮时,总是会出现错误 这两行是错的Java 异常设置背景色,java,android,nullpointerexception,Java,Android,Nullpointerexception,我对我的代码有一个问题,它应该更改我开始活动的背景色。我应该用单选按钮(在RadioGroup中)在蓝色和红色之间进行选择。当我点击设置菜单中的红色/蓝色单选按钮时,总是会出现错误 这两行是错的 ChangeToRed(background); background.setBackgroundColor(0x0000FF00); java.lang.NullPointerException:尝试对空对象引用调用虚拟方法“void android.widget.RelativeLayout.se
ChangeToRed(background); background.setBackgroundColor(0x0000FF00);
java.lang.NullPointerException:尝试对空对象引用调用虚拟方法“void android.widget.RelativeLayout.setBackgroundColor(int)”
在com.example.clecks.reaction\u game.activity\u settings.ChangeToBlue(activity\u settings.java:67)
在com.example.clecks.reaction\u game.activity\u settings$2.onCheckedChanged(activity\u settings.java:42)
以下是我的java代码:
public class activity_settings extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_activity_settings);
ColorChange();
}
public void ColorChange() {
final RelativeLayout background = (RelativeLayout) findViewById(R.id.start);
final RadioButton ChangeToBlue = (RadioButton) findViewById(R.id.button_blue);
final RadioButton ChangeToRed = (RadioButton) findViewById(R.id.button_red);
final Button button_save = (Button) findViewById(R.id.button_save);
button_save.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
ChangeOption(background);
}
});
ChangeToBlue.setOnCheckedChangeListener(new RadioButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
ChangeToBlue(background);
}
});
ChangeToRed.setOnCheckedChangeListener(new RadioButton.OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
ChangeToRed(background);
}
});
}
public void ChangeOption(RelativeLayout background) {
if (background.isEnabled()) {
background.setEnabled(false);
} else {
background.setEnabled(true);
}
}
public void ChangeToBlue(RelativeLayout background) {
background.setBackgroundColor(Color.BLUE);
background.invalidate();
}
public void ChangeToRed(RelativeLayout background) {
background.setBackgroundColor(Color.RED);
background.invalidate();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_activity_settings, 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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}}
XML代码:
<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:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.example.clecks.reaction_game.activity_settings">
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Einstellungen"
android:id="@+id/textView2"
android:layout_gravity="center_horizontal" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceSmall"
android:id="@+id/textView3"
android:layout_gravity="center_horizontal" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Singalton"
android:id="@+id/textView4"
android:layout_gravity="center_horizontal" />
<RadioGroup
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal">
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New RadioButton"
android:id="@+id/radioButton"
android:layout_gravity="center_horizontal"
android:checked="false" />
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New RadioButton"
android:id="@+id/radioButton2"
android:layout_gravity="center_horizontal" />
</RadioGroup>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textView5"
android:layout_gravity="center_horizontal" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Hintergrundfarbe"
android:id="@+id/textView6"
android:layout_gravity="center_horizontal" />
<RadioGroup
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:id="@+id/RadioGroup_Color">
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Rot"
android:id="@+id/button_red"
android:checked="false"
android:layout_gravity="center_horizontal" />
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Blau"
android:id="@+id/button_blue"
android:checked="false"
android:layout_gravity="center_horizontal" />
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Grün"
android:id="@+id/button_green"
android:checked="false"
android:layout_gravity="center_horizontal" />
</RadioGroup>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textView7"
android:layout_gravity="center_horizontal" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Spielmodus"
android:id="@+id/textView8"
android:layout_gravity="center_horizontal" />
<RadioGroup
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal">
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Handy"
android:id="@+id/radioButton6"
android:layout_gravity="center_horizontal"
android:checked="false" />
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Wii-Mote"
android:id="@+id/radioButton7"
android:layout_gravity="center_horizontal"
android:checked="false" />
</RadioGroup>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textView9"
android:layout_gravity="center_horizontal" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textView10"
android:layout_gravity="center_horizontal" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Speichern"
android:id="@+id/button_save"
android:layout_gravity="center_horizontal" />
</LinearLayout>
正如您的例外情况所述,方法
相对.setBackgroundColor
需要int
尝试在com.example.clecks.reaction\u game.activity\u settings.changeToBlue上的空对象引用上调用虚拟方法“void android.widget.RelativeLayout.setBackgroundColor(int)”
不必硬编码颜色,您可以使用:
public void changeToBlue(RelativeLayout background) {
background.setBackgroundColor(Color.BLUE);
background.invalidate();
}
public void changeToRed(RelativeLayout background) {
background.setBackgroundColor(Color.RED);
background.invalidate();
}
.您的布局中没有
R.id.start
,因此findViewById(R.id.start)
返回null。检查背景变量是否不为null如何。另外,尝试对类使用java命名约定start是另一个活动,我想我可以使用以下行更改start活动背景的颜色:O