Android 重写 onDraw() 问题
我这里有一个小问题是我到目前为止的代码：
public class MainActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new GraphicView(this));
TextView mainLabel = (TextView)findViewById(R.id.title);
mainLabel.setText("Android Circle Path");
}
static class GraphicView extends View{
public GraphicView(Context context){
super(context);
}
@Override
public void onDraw(Canvas canvas){
}
}
}
和 main.xml 文件：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="30dip"
>
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginLeft="20dip"
android:layout_marginRight="20dip">
<TextView
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginBottom="20dip"
android:textSize="24.5sp"
android:id="@+id/title">
</TextView>
</LinearLayout>
</LinearLayout>
当我尝试在 onDraw() 函数中设置文本时，应用程序崩溃了，我做错了什么？
I have a small issue here is the code i have so far:
public class MainActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new GraphicView(this));
TextView mainLabel = (TextView)findViewById(R.id.title);
mainLabel.setText("Android Circle Path");
}
static class GraphicView extends View{
public GraphicView(Context context){
super(context);
}
@Override
public void onDraw(Canvas canvas){
}
}
}
And the main.xml file:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="30dip"
>
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginLeft="20dip"
android:layout_marginRight="20dip">
<TextView
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginBottom="20dip"
android:textSize="24.5sp"
android:id="@+id/title">
</TextView>
</LinearLayout>
</LinearLayout>
When i try to set the text in the onDraw() function the app crashes, what am i doing wrong?
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视图的
onDraw方法应该用于单独渲染到该视图。您不应该在另一个视图中调用 UI 更新方法。将用于设置标题的代码移至 Activity 的onCreate方法中，因为只需执行一次。然后只需在自定义视图中绘制圆圈即可。另外，由于您的自定义视图未实现 ViewParent，因此不应使用它来保存标题 TextView。重新组织 xml 以将标题视图移到 GraphicsView 之外A view's
onDrawmethod should be used to render to that view alone. You should not be calling UI update methods in another view. Move the code for setting the title into your activity'sonCreatemethod, since that only needs to be done once. Then just draw your circle in your custom view. Also, since your custom view does not implement ViewParent, it shouldn't be used to hold the title TextView. Reorganize your xml to move the title view outside the GraphicsViewTextView是在该Activity的onCreate方法中创建的局部变量。因此，TextView的范围仅限于onCreate方法内。您无法在该方法之外访问它。此外，您尝试做的事情不是正确的方法，在 GraphView 的 onDraw 方法中，您应该单独绘制 GraphView 组件，不是外面的景色或其他任何东西。TextViewis a local variable created in theonCreatemethod of thatActivity. So the scope ofTextViewis confined within thatonCreatemethod only. You can't access it outside that method. Moreover what you are trying to do is not the right way, insideGraphView'sonDrawmethod you are supposed to draw theGraphViewcomponents alone, not the outside views or anything else.