我在android中制作了一个非常简单的绘图应用程序，因为我使用了拾色器来选择不同的笔彩，我已经实现了如下，但是单击“颜色”按钮时。我的应用程序不幸地停止了（崩溃）..我的代码是如下，请帮助我解决我的问题。
Main.java
package com.example.singletouch;
import android.os.Bundle;
import android.app.ActionBar.LayoutParams;
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.HorizontalScrollView;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;
public class MainActivity extends Activity implements
ColorPickerDialog.OnColorChangedListener {
ImageView pen, color;
SingleTouchView mDrawView;
RelativeLayout layout, layout1;
ImageView remove;
ImageView eraser;
private LinearLayout list_color;
LinearLayout pens;
private TextView select_color;
private int selectedColor = 0x00FF0000;
HorizontalScrollView myplate;
private Paint mPaint, mBitmapPaint;
private Path mPath;
public Canvas mCanvas;
LinearLayout pen1, pen2, pen3, pen4;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDrawView = (SingleTouchView) findViewById(R.id.myview);
layout1 = (RelativeLayout) findViewById(R.id.layout1);
layout = (RelativeLayout) findViewById(R.id.layout);
pen = (ImageView) findViewById(R.id.pen);
pens = (LinearLayout) findViewById(R.id.linear);
pens.setVisibility(View.GONE);
pen1 = (LinearLayout) findViewById(R.id.pen1);
pen2 = (LinearLayout) findViewById(R.id.pen2);
pen3 = (LinearLayout) findViewById(R.id.pen3);
pen4 = (LinearLayout) findViewById(R.id.pen4);
eraser = (ImageView) findViewById(R.id.eraser);
remove = (ImageView) findViewById(R.id.remove);
color = (ImageView) findViewById(R.id.color);
pen.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
pens.setVisibility(View.VISIBLE);
}
});
pens.setVisibility(View.GONE);
pen1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mDrawView.setPen(SingleTouchView.DrawingPens.PEN_1);
pens.setVisibility(View.GONE);
}
});
pen2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mDrawView.setPen(SingleTouchView.DrawingPens.PEN_2);
pens.setVisibility(View.GONE);
}
});
pen3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
pens.setVisibility(View.GONE);
mDrawView.setPen(SingleTouchView.DrawingPens.PEN_3);
}
});
pen4.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
pens.setVisibility(View.GONE);
mDrawView.setPen(SingleTouchView.DrawingPens.PEN_4);
}
});
remove.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
layout.removeView(mDrawView);
mDrawView = new SingleTouchView(MainActivity.this);
layout.addView(mDrawView);
}
});
eraser.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mBitmapPaint.setColor(Color.TRANSPARENT);
mPath.reset();
mDrawView.invalidate();
}
});
color.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
// myplate.setVisibility(View.VISIBLE);
new ColorPickerDialog(MainActivity.this, MainActivity.this,
mPaint.getColor()).show();
}
});
}
@Override
public void colorChanged(int color) {
// TODO Auto-generated method stub
}
}
ColorPickerDialog.java
package com.example.singletouch;
import android.app.Dialog;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ColorMatrix;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.SweepGradient;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
public class ColorPickerDialog extends Dialog{
public interface OnColorChangedListener {
void colorChanged(int color);
}
private OnColorChangedListener mListener;
private int mInitialColor;
private static class ColorPickerView extends View {
private Paint mPaint;
private Paint mCenterPaint;
private final int[] mColors;
private OnColorChangedListener mListener;
ColorPickerView(Context c, OnColorChangedListener l, int color) {
super(c);
mListener = l;
mColors = new int[] {
0xFFFF0000, 0xFFFF00FF, 0xFF0000FF, 0xFF00FFFF, 0xFF00FF00,
0xFFFFFF00, 0xFFFF0000
};
Shader s = new SweepGradient(0, 0, mColors, null);
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setShader(s);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeWidth(32);
mCenterPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mCenterPaint.setColor(color);
mCenterPaint.setStrokeWidth(5);
}
private boolean mTrackingCenter;
private boolean mHighlightCenter;
protected void onDraw(Canvas canvas) {
float r = CENTER_X - mPaint.getStrokeWidth()*0.5f;
canvas.translate(CENTER_X, CENTER_X);
canvas.drawOval(new RectF(-r, -r, r, r), mPaint);
canvas.drawCircle(0, 0, CENTER_RADIUS, mCenterPaint);
if (mTrackingCenter) {
int c = mCenterPaint.getColor();
mCenterPaint.setStyle(Paint.Style.STROKE);
if (mHighlightCenter) {
mCenterPaint.setAlpha(0xFF);
} else {
mCenterPaint.setAlpha(0x80);
}
canvas.drawCircle(0, 0,
CENTER_RADIUS + mCenterPaint.getStrokeWidth(),
mCenterPaint);
mCenterPaint.setStyle(Paint.Style.FILL);
mCenterPaint.setColor(c);
}
}
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(CENTER_X*2, CENTER_Y*2);
}
private static final int CENTER_X = 100;
private static final int CENTER_Y = 100;
private static final int CENTER_RADIUS = 32;
private int floatToByte(float x) {
int n = java.lang.Math.round(x);
return n;
}
private int pinToByte(int n) {
if (n < 0) {
n = 0;
} else if (n > 255) {
n = 255;
}
return n;
}
private int ave(int s, int d, float p) {
return s + java.lang.Math.round(p * (d - s));
}
private int interpColor(int colors[], float unit) {
if (unit <= 0) {
return colors[0];
}
if (unit >= 1) {
return colors[colors.length - 1];
}
float p = unit * (colors.length - 1);
int i = (int)p;
p -= i;
// now p is just the fractional part [0...1) and i is the index
int c0 = colors[i];
int c1 = colors[i+1];
int a = ave(Color.alpha(c0), Color.alpha(c1), p);
int r = ave(Color.red(c0), Color.red(c1), p);
int g = ave(Color.green(c0), Color.green(c1), p);
int b = ave(Color.blue(c0), Color.blue(c1), p);
return Color.argb(a, r, g, b);
}
private int rotateColor(int color, float rad) {
float deg = rad * 180 / 3.1415927f;
int r = Color.red(color);
int g = Color.green(color);
int b = Color.blue(color);
ColorMatrix cm = new ColorMatrix();
ColorMatrix tmp = new ColorMatrix();
cm.setRGB2YUV();
tmp.setRotate(0, deg);
cm.postConcat(tmp);
tmp.setYUV2RGB();
cm.postConcat(tmp);
final float[] a = cm.getArray();
int ir = floatToByte(a[0] * r + a[1] * g + a[2] * b);
int ig = floatToByte(a[5] * r + a[6] * g + a[7] * b);
int ib = floatToByte(a[10] * r + a[11] * g + a[12] * b);
return Color.argb(Color.alpha(color), pinToByte(ir),
pinToByte(ig), pinToByte(ib));
}
private static final float PI = 3.1415926f;
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX() - CENTER_X;
float y = event.getY() - CENTER_Y;
boolean inCenter = java.lang.Math.sqrt(x*x + y*y) <= CENTER_RADIUS;
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mTrackingCenter = inCenter;
if (inCenter) {
mHighlightCenter = true;
invalidate();
break;
}
case MotionEvent.ACTION_MOVE:
if (mTrackingCenter) {
if (mHighlightCenter != inCenter) {
mHighlightCenter = inCenter;
invalidate();
}
} else {
float angle = (float)java.lang.Math.atan2(y, x);
// need to turn angle [-PI ... PI] into unit [0....1]
float unit = angle/(2*PI);
if (unit < 0) {
unit += 1;
}
mCenterPaint.setColor(interpColor(mColors, unit));
invalidate();
}
break;
case MotionEvent.ACTION_UP:
if (mTrackingCenter) {
if (inCenter) {
mListener.colorChanged(mCenterPaint.getColor());
}
mTrackingCenter = false; // so we draw w/o halo
invalidate();
}
break;
}
return true;
}
}
public ColorPickerDialog(Context context,
OnColorChangedListener listener,
int initialColor) {
super(context);
mListener = listener;
mInitialColor = initialColor;
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
OnColorChangedListener l = new OnColorChangedListener() {
public void colorChanged(int color) {
mListener.colorChanged(color);
dismiss();
}
};
setContentView(new ColorPickerView(getContext(), l, mInitialColor));
setTitle("Pick a Color");
}
}
Logcat
08-06 13:16:17.164: E/AndroidRuntime(2421): FATAL EXCEPTION: main
08-06 13:16:17.164: E/AndroidRuntime(2421): java.lang.NullPointerException
08-06 13:16:17.164: E/AndroidRuntime(2421): at com.example.singletouch.MainActivity$8.onClick(MainActivity.java:184)
08-06 13:16:17.164: E/AndroidRuntime(2421): at android.view.View.performClick(View.java:3511)
08-06 13:16:17.164: E/AndroidRuntime(2421): at android.view.View$PerformClick.run(View.java:14109)
08-06 13:16:17.164: E/AndroidRuntime(2421): at android.os.Handler.handleCallback(Handler.java:605)
08-06 13:16:17.164: E/AndroidRuntime(2421): at android.os.Handler.dispatchMessage(Handler.java:92)
08-06 13:16:17.164: E/AndroidRuntime(2421): at android.os.Looper.loop(Looper.java:137)
08-06 13:16:17.164: E/AndroidRuntime(2421): at android.app.ActivityThread.main(ActivityThread.java:4424)
08-06 13:16:17.164: E/AndroidRuntime(2421): at java.lang.reflect.Method.invokeNative(Native Method)
08-06 13:16:17.164: E/AndroidRuntime(2421): at java.lang.reflect.Method.invoke(Method.java:511)
08-06 13:16:17.164: E/AndroidRuntime(2421): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
08-06 13:16:17.164: E/AndroidRuntime(2421): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
08-06 13:16:17.164: E/AndroidRuntime(2421): at dalvik.system.NativeStart.main(Native Method)
...
请帮我..！
最佳答案
您尚未在mPaint中初始化MainActivity.java
new ColorPickerDialog(MainActivity.this, MainActivity.this,
mPaint.getColor()).show();
您仅将其声明为班级成员，但未初始化。
在
onCreate中 mPaint = new Paint();