问题描述
我是android新手,有点卡住。我正在尝试创建一个简单的绘图应用程序,该应用程序在页面顶部显示一个示例,在页面下方显示一个正方形空间。目的是展示一封信,一个孩子需要练习以复制它。
我在布局中包括绘图类时遇到麻烦,需要限制其边界。
这是主要布局
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/exampleText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="32dp"
android:text="TextView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<androidx.constraintlayout.widget.ConstraintLayout
enter code here` android:id="@+id/drawingBoard"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/exampleText">
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
这是PaintView类
import android.app.ActionBar;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
public class PaintView extends View {
public ViewGroup.LayoutParams param;
private Path path = new Path();
private Paint brush = new Paint();
public PaintView(MainActivity context) {
super(context);
brush.setAntiAlias(true);
brush.setColor(Color.RED);
brush.setStyle(Paint.Style.stroke);
brush.setstrokeJoin(Paint.Join.ROUND);
brush.setstrokeWidth(8f);
param = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,ViewGroup.LayoutParams.WRAP_CONTENT);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float pointX = event.getX();
float pointY = event.getY();
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
path.moveto(pointX,pointY);
return true;
case MotionEvent.ACTION_MOVE:
path.lineto(pointX,pointY);
break;
default:
return false;
}
postInvalidate();
return false;
}
@Override
protected void onDraw(Canvas canvas) {
canvas.drawPath(path,brush);
}
这是在“主要活动”中的调用方式
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
PaintView paintView = new PaintView(this);
setContentView(paintView);
}
我需要将绘图板安装到“ drawingBoard”中。
这不一定是正确的方法,但这是我所知。
预先感谢
解决方法
将customview附加到一个片段。 这是一种完全不同的方法,因此您将不得不对代码进行很多更改。
另一种方法是将视图以编程方式添加到ConstraintLayout中。 在MainActivity中,
protected void onCreate(Bundle savedInstanceStatee) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//remove those lines.
/*
PaintView paintView = new PaintView(this);
setContentView(paintView);*/
ConstraintLayout parentLayout = (ConstraintLayout)findViewById(R.id.drawingBoard);
ConstraintSet set = new ConstraintSet();
PaintView paintView = new PaintView(this);
// set view id,else getId() returns -1
paintView.setId(View.generateViewId());
layout.addView(paintView,0);
set.clone(parentLayout);
// connect start and end point of views,in this
case top of child to top of parent.
set.connect(paintView.getId(),ConstraintSet.TOP,parentLayout.getId(),60);
// ... similarly add other constraints
set.applyTo(parentLayout);
}
,
在活动中,您仅用绘画视图覆盖内容视图:
setContentView(paintView);
删除该行。
改为在XML中添加PaintView
:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/exampleText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="32dp"
android:text="TextView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<!-- TODO: Replace with your package name -->
<com.example.PaintView
android:id="@+id/drawingBoard"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/exampleText" />
</androidx.constraintlayout.widget.ConstraintLayout>
使用这种方法,您必须在其构造函数中膨胀自定义视图:
public class PaintView extends ConstraintLayout {
public PaintView(@NonNull Context context) {
super(context);
init();
}
public PaintView(@NonNull Context context,@Nullable AttributeSet attrs) {
super(context,attrs);
init();
}
public PaintView(@NonNull Context context,@Nullable AttributeSet attrs,int defStyleAttr) {
super(context,attrs,defStyleAttr);
init();
}
public PaintView(@NonNull Context context,int defStyleAttr,int defStyleRes) {
super(context,defStyleAttr,defStyleRes);
init();
}
public void init() {
inflate(getContext(),R.layout.layout_product_item,this);
}
}
要与活动代码中的PaintView
进行交互,您可以执行以下操作:
PaintView paintView = (PaintView) findViewById(R.id.drawingBoard);