问题描述
我正在尝试在 drawline(activity) 中创建一个指状线(class) 对象。指状线采用 MainActivity(activity) 的上下文。我得到 ClassCastException 表明这一点
Process: com.example.caddrawingtool,PID: 11405
java.lang.RuntimeException: Unable to instantiate application
com.example.caddrawingtool.MainActivity: java.lang.classCastException:
com.example.caddrawingtool.MainActivity cannot be cast to android.app.Application
at android.app.LoadedApk.makeApplication(LoadedApk.java:1226)
at android.app.ActivityThread.handleBindApplication(ActivityThread.java:6504)
at android.app.ActivityThread.access$1400(ActivityThread.java:229)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1892)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7436)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:980)
我已将绘制线中的 getApplicationContext() 更改为使用
this
我无法使用
MainActivity.this
虽然。
有没有办法简化这一切？ 我的主活动代码：
public class MainActivity extends AppCompatActivity {
fingerline dv;
private Paint mpaint;
private Context context;
MainActivity MainActivity(){
return MainActivity.this;
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
dv = new fingerline(this);
setContentView(dv);
dv.setBackgroundColor(Color.BLACK);
mpaint = new Paint();
mpaint.setAntiAlias(true);
mpaint.setDither(true);
mpaint.setColor(Color.WHITE);
mpaint.setStyle(Paint.Style.stroke);
mpaint.setstrokeJoin(Paint.Join.MITER);
mpaint.setstrokeCap(Paint.Cap.ROUND);
mpaint.setstrokeWidth(12);
getSupportActionBar().setTitle("3D TOOL");
getSupportActionBar().setdisplayHomeAsUpEnabled(true);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.my_menu,menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onoptionsItemSelected(@NonNull MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.line:
Intent intent = new Intent(this,drawline2.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
this.startActivity(intent);
break;
case R.id.circle:
Intent intent1=new Intent(this,drawcircle.class);
intent1.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
this.startActivity(intent1);
break;
case R.id.rectangle:
Intent intent2=new Intent(this,drawrectangle.class);
intent2.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
this.startActivity(intent2);
break;
case R.id.offset:
break;
default:
break;
}
return super.onoptionsItemSelected(item);
}
我的指纹代码：
public class fingerline extends View {
public int width,height;
private Bitmap mbitmap;
private Canvas mcanvas;
private Paint mpaint,mbitmappaint,circlepaint;
private float startx;
private float starty;
private float endx;
private float endy;
private Path path,circlepath;
Context c;
public fingerline(Context context) {
super(context);
// c = context;
path = new Path();
mpaint = new Paint();
mbitmappaint = new Paint(Paint.DITHER_FLAG);
circlepaint = new Paint();
circlepath = new Path();
circlepaint.setAntiAlias(true);
circlepaint.setColor(Color.WHITE);
circlepaint.setStyle(Paint.Style.stroke);
circlepaint.setstrokeJoin(Paint.Join.MITER);
circlepaint.setstrokeWidth(4f);
}
@Override
protected void onSizeChanged(int w,int h,int oldw,int oldh) {
super.onSizeChanged(w,h,oldw,oldh);
mbitmap = Bitmap.createBitmap(w,Bitmap.Config.ARGB_8888);
mcanvas = new Canvas(mbitmap);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
mpaint.setStyle(Paint.Style.stroke);
mpaint.setColor(Color.WHITE);
mpaint.setstrokeWidth(12);
mpaint.setAntiAlias(true);
mpaint.setDither(true);
mpaint.setstrokeJoin(Paint.Join.MITER);
mpaint.setstrokeCap(Paint.Cap.ROUND);
canvas.drawBitmap(mbitmap,mbitmappaint);
canvas.drawPath(path,mpaint);
canvas.drawPath(circlepath,circlepaint);
}
private float mX,mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x,float y) {
path.reset();
path.moveto(x,y);
mX = x;
mY = y;
}
private void touch_move(float x,float y) {
float dX = Math.abs(x - mX);
float dY = Math.abs(y - mY);
if (dX >= TOUCH_TOLERANCE) {
path.quadTo(mX,mY,(x + mX) / 2,(y + mY) / 2);
mX = x;
mY = y;
}
}
private void touch_up() {
path.lineto(mX,mY);
circlepath.reset();
mcanvas.drawPath(path,mpaint);
path.reset();
}
@SuppressLint("ClickableViewAccessibility")
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
startx = event.getX();
starty = event.getY();
touch_start(startx,starty);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
startx = event.getX();
starty = event.getY();
touch_move(startx,starty);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
我的画线代码：
public class drawline2 extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_drawline2);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
EditText editText,editText1;
editText = (EditText) findViewById(R.id.length);
editText1 = (EditText) findViewById(R.id.angle);
Canvas canvas;
Paint paint = new Paint();
Paint circlepaint = new Paint();
Path path = new Path();
Path cpath = new Path();
circlepaint.setAntiAlias(true);
circlepaint.setstrokeWidth(4f);
circlepaint.setColor(Color.WHITE);
circlepaint.setStyle(Paint.Style.stroke);
circlepaint.setstrokeJoin(Paint.Join.MITER);
fingerline dv;
dv = new fingerline(this);
dv.setBackgroundColor(Color.BLACK);
setContentView(dv);
circlepaint.setAntiAlias(true);
circlepaint.setDither(true);
String value = editText.getText().toString();
int length =0;
double angle=0;
if(value!=null && value.length()>0){
try{
length = Integer.parseInt(value);
}
catch (NullPointerException e){
length=0;
}
}
String value1 = editText1.getText().toString();
if(value1!=null && value1.length()>0){
try{
angle = Double.parseDouble(value1);
}
catch (NullPointerException e){
angle=0;
}
}
int startX,startY,endX,endY,x,y;
x= 0;
y=0;
path.reset();
path.moveto(x,y);
startX = (int) x;
startY = (int) y;
endY = (int) (x + length * Math.cos(angle));
endX = (int) (x + length * Math.sin(angle));
FloatingActionButton fab = findViewById(R.id.fab);
fab.setonClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view,"Replace with your own action",Snackbar.LENGTH_LONG)
.setAction("Action",null).show();
}
});
}
} 提前致谢。
解决方法
简而言之：
MainActivity 无法转换为 android.app.Application
您可以通过将其命名为 DrawlineActivity 和 FingerlineActivity 使其更具可读性。然后只需使用 this 或 DrawlineActivity.this 作为 Context。