[英]How to draw Canvas on View
我想使用 canvas 在 View 上绘制文本。
这是我尝试执行此操作的一些代码。
public class MainActivity extends AppCompatActivity {
View view;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
view=findViewById(R.id.viewOfText);
Canvas canvas = new Canvas();
Paint paint = new Paint();
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.FILL);
paint.setTextSize(40f);
canvas.drawText("Text", 10, 25, paint);
view.draw(canvas);
view.invalidate();
}
}
但我没有看到任何结果
为扩展View
的Canvas
创建新 class 的更常用方法
例如
DrawText.java
package com.test.canvas;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
public class DrawText extends View {
Paint paint = new Paint();
private void init() {
paint.setColor(Color.BLACK);
}
public DrawText(Context context) {
super(context);
init();
}
public DrawText(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public DrawText(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
@Override
public void onDraw(Canvas canvas) {
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.FILL);
paint.setTextSize(40f);
canvas.drawText("Text", 100, 100, paint);
}
}
activity_main.xml
<?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">
<com.test.canvas.DrawText
android:id="@+id/DrawText"
android:layout_width="match_parent"
android:layout_height="match_parent">
</com.test.canvas.DrawText>
</androidx.constraintlayout.widget.ConstraintLayout>
MainActivity.java
package com.test.canvas;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
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