公共类CustomKeyboardView扩展KeyboardView {

public CustomKeyboardView(Context context, AttributeSet attrs) {

super(context, attrs);

}

@Override

public void onDraw(Canvas canvas) {

super.onDraw(canvas);

Paint paintBackground = new Paint();

paintBackground.setTextAlign(Paint.Align.CENTER);

paintBackground.setTextSize(48);

paintBackground.setColor(Color.YELLOW);

List keys = getKeyboard().getKeys();

for(Key key: keys) {

if(key.label != null && key.codes[0] == 110)

canvas.drawRect(key.x, key.y, key.x+key.width, key.y+key.height, paintBackground);

paintBackground.setColor(Color.WHITE);

canvas.drawText(key.label.toString(), key.x + (key.width/2),

key.y + (key.height/2), paintBackground);

}

}

}

奇怪的是，如果我注释掉帆布drawRect中或帆布的drawText，另一个工作正常，但如果我离开他们都在，我得到这个错误：

FATAL EXCEPTION: main Process: com.alpha.alphaproto, PID: 6540

java.lang.NullPointerException

at com.alpha.alphaproto.CustomKeyboardView.onDraw(CustomKeyboardView.java:48)

at android.view.View.draw(View.java:14465)

at android.view.View.getDisplayList(View.java:13362)

at android.view.View.getDisplayList(View.java:13404)

at android.view.View.draw(View.java:14182)

at android.view.ViewGroup.drawChild(ViewGroup.java:3103)

at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2940)

at android.view.View.getDisplayList(View.java:13357)

at android.view.View.getDisplayList(View.java:13404)

at android.view.View.draw(View.java:14182)

at android.view.ViewGroup.drawChild(ViewGroup.java:3103)

at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2940)

at android.view.View.draw(View.java:14468)

at android.widget.FrameLayout.draw(FrameLayout.java:472)

at android.view.View.getDisplayList(View.java:13362)

at android.view.View.getDisplayList(View.java:13404)

at android.view.View.draw(View.java:14182)

at android.view.ViewGroup.drawChild(ViewGroup.java:3103)

at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2940)

at android.view.View.getDisplayList(View.java:13357)

at android.view.View.getDisplayList(View.java:13404)

at android.view.View.draw(View.java:14182)

at android.view.ViewGroup.drawChild(ViewGroup.java:3103)

at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2940)

at android.view.View.draw(View.java:14468)

at android.widget.FrameLayout.draw(FrameLayout.java:472)

at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2326)

at android.view.View.getDisplayList(View.java:13362)

at android.view.View.getDisplayList(View.java:13404)

at android.view.HardwareRenderer$GlRenderer.buildDisplayList(HardwareRenderer.java:1570)

at android.view.HardwareRenderer$GlRenderer.draw(HardwareRenderer.java:1449)

at android.view.ViewRootImpl.draw(ViewRootImpl.java:2377)

at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2249)

at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1879)

at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:996)

at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5600)

at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)

at android.view.Choreographer.doCallbacks(Choreographer.java:574)

at android.view.Choreographer.doFrame(Choreographer.java:544)

at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)

at android.os.Handler.handleCallback(Handler.java:733)

at android.os.Handler.dispatchMessage(Handler.java:95)

at android.os.Looper.loop(Looper.java:136)

at android.app.ActivityThread.main(ActivityThread.java:5001)

at java.lang.reflect.Method.invokeNative(Native Method)

at java.lang.reflect.Method.invoke(Method.java:515)

at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)

at dalvik.system.NativeStart.main(Native Method

我大惑不解。任何帮助将非常感激。

2016-07-25

scrayne