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崩溃时
所以我试着用一个按钮的点击,但应用程序崩溃切换活动,我也得到了logcat的错误应用程序切换活动
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at jake.poewiki.Red.onCreate(Red.java:22)
的XML对于该按钮
<Button
android:background="@android:color/holo_orange_dark"
android:textColor="#ffffff"
android:id="@+id/GoToRed"
android:layout_width="78dp"
android:layout_height="48dp"
android:text="Red"
app:layout_constraintTop_toTopOf="parent"
android:layout_marginTop="519dp"
android:layout_marginLeft="0dp"
app:layout_constraintLeft_toLeftOf="parent" />
的Java进行了onclicklistner
public class Gems extends AppCompatActivity {
Button GoRed, GoGreen, GoBlue, GoWhite, GoUniqueGems, GoHome, GoClasses, GoItems;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_gems);
GoGreen = (Button) findViewById(R.id.GotoGreen);
GoRed = (Button) findViewById(R.id.GoToRed);
GoBlue = (Button) findViewById(R.id.GoToBlue);
GoWhite = (Button) findViewById(R.id.GoToWhite);
GoUniqueGems = (Button) findViewById(R.id.GoToUnique);
GoHome = (Button) findViewById(R.id.GoToHome);
GoItems = (Button) findViewById(R.id.GoToItems);
GoClasses = (Button) findViewById(R.id.GoToClasses);
GoRed.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent GoRed = new Intent(Gems.this, Red.class);
startActivity(GoRed);
}
});
的OnCreate为Red.java
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_red);
GoGems = (Button) findViewById(R.id.GoToGems);
GoItems = (Button) findViewById(R.id.GoToItems);
GoHome = (Button) findViewById(R.id.GoToHome);
GoClasses = (Button) findViewById(R.id.GoToClasses);
第22行是在点击监听器,允许用户回到宝石页面
GoGems.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent GoGems = new Intent(Red.this, Gems.class);
startActivity(GoGems);
你能表现出更多这样的代码?它在一个方法里面吗? – codeMagic
更新它与更多的代码假设你的意思是java不xml –
显示更多的代码,你定义的按钮 –