我正在尝试使用处理程序更改 Activity 的背景颜色,但收到错误消息“尝试调用虚拟方法”。
这是我的代码
public class MainActivity extends AppCompatActivity {
private EditText editTextUser, editTextPass;
private RelativeLayout relativeLayoutMain;
private Random random = new Random();
Intent intent;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
relativeLayoutMain = (RelativeLayout) findViewById(R.id.relativeLayoutMain);
Button btnSignIn = (Button) findViewById(R.id.buttonSignIn);
btnSignIn.setEnabled(false);
handler.postDelayed(runner, 2000);
Button buttonSignUp = (Button) findViewById(R.id.buttonSignUp);
buttonSignUp.setText("Not registered? CLICK HERE");
editTextUser = (EditText) findViewById(R.id.editTextUser);
editTextPass = (EditText) findViewById(R.id.editTextPassword);
if (editTextUser.getText().toString() != null && editTextPass.getText().toString() != null) {
btnSignIn.setEnabled(true);
}
}
android.content.res.Resources res = getResources();
int[] clrItems = res.getIntArray(R.array.color_background);
List<int[]> arrayOfColor = new ArrayList<int[]>();
public List<int[]> getArrayOfColor() {
arrayOfColor.add(clrItems);
return arrayOfColor;
}
Runnable runner = new Runnable() {
@Override
public void run() {
Log.e("run: ", "call");
Bitmap bitmap = Bitmap.createBitmap(612, 612, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
final int clr = 0xFF424242;
final Paint paint = new Paint();
final Rect destRect = new Rect((612-bitmap.getWidth())/2,
24,
(612)-(612-bitmap.getWidth())/2,
612-24);
final RectF rectF = new RectF(destRect);
final Rect srcRect = new Rect(0, 0, bitmap.getWidth(), 612);
final float roundPx = 612;
paint.setAntiAlias(true);
canvas.drawARGB(0, 0, 0, 0);
paint.setColor(clr);
canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawBitmap(bitmap, srcRect, destRect, paint);
GradientDrawable gd = new GradientDrawable(GradientDrawable.Orientation.LEFT_RIGHT, new int[]{0xFF616261, 0xFF131313});
gd.setCornerRadius(0f);
relativeLayoutMain.setBackground(gd);
handler.postDelayed(runner, 4000);
}
};
public void login(View view) {
intent = new Intent(this, HomeActivity.class);
startActivity(intent);
}
public void register(View view) {
intent = new Intent(this, SignUpActivity.class);
startActivity(intent);
}
}
这是我的 logcat。
08-31 16:29:47.122 13152-13152/com.example.salimshivani.student E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.salimshivani.student, PID: 13152
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.salimshivani.student/com.example.salimshivani.student.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3132)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
at android.app.ActivityThread.access$1100(ActivityThread.java:229)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7325)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.content.ContextWrapper.getResources(ContextWrapper.java:92)
at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)
at com.example.salimshivani.student.MainActivity.<init>(MainActivity.java:241)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1096)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3122)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
at android.app.ActivityThread.access$1100(ActivityThread.java:229)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7325)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
请帮助我不断移动 Activity 的背景颜色。
提前致谢
最佳答案
您调用方法 getResources()
作为类初始化的一部分(在任何方法之外,因此它将作为构造函数的一部分执行)
此时,Activity
实例还不存在,因此它可能不会调用需要实例存在的方法。
将导致Exception
的语句,因为它们利用了Activity
是一种Context
的事实:
android.content.res.Resources res = getResources();
int[] clrItems = res.getIntArray(R.array.color_background);
另一方面,以下语句不会引起问题,因为它只是普通的旧 Java:
List arrayOfColor = new ArrayList();
只需将“问题陈述”粘贴到一个方法中,例如onCreate()
// declare here
android.content.res.Resources res;
int[] clrItems;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// initialise here
res = getResources();
clrItems = res.getIntArray(R.array.color_background);
relativeLayoutMain = (RelativeLayout) findViewById(R.id.relativeLayoutMain);
Button btnSignIn = (Button) findViewById(R.id.buttonSignIn);
btnSignIn.setEnabled(false);
...
}
关于android - 尝试调用 Resources 中的虚拟方法 res = getResources();,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/39249907/