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 场景一：自定义进度条

在很多应用中，我们会看到一些独特样式的进度条，接下来就实现一个简单的圆形进度条。

实现思路

• 继承 View 类。
• 重写 onDraw 方法，在该方法里使用 Canvas 和 Paint 来绘制圆形进度条。
• 提供更新进度的方法。

示例代码

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.View;public class CustomProgressBar extends View {private Paint backgroundPaint;private Paint progressPaint;private int progress = 0;private RectF rectF;public CustomProgressBar(Context context) {super(context);init();}public CustomProgressBar(Context context, AttributeSet attrs) {super(context, attrs);init();}public CustomProgressBar(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);init();}private void init() {backgroundPaint = new Paint();backgroundPaint.setColor(Color.GRAY);backgroundPaint.setStyle(Paint.Style.STROKE);backgroundPaint.setStrokeWidth(20);backgroundPaint.setAntiAlias(true);progressPaint = new Paint();progressPaint.setColor(Color.BLUE);progressPaint.setStyle(Paint.Style.STROKE);progressPaint.setStrokeWidth(20);progressPaint.setAntiAlias(true);rectF = new RectF();}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);int centerX = getWidth() / 2;int centerY = getHeight() / 2;int radius = Math.min(centerX, centerY) - 20;rectF.set(centerX - radius, centerY - radius, centerX + radius, centerY + radius);// 绘制背景圆形canvas.drawArc(rectF, 0, 360, false, backgroundPaint);// 绘制进度弧形float sweepAngle = (progress / 100.0f) * 360;canvas.drawArc(rectF, -90, sweepAngle, false, progressPaint);}public void setProgress(int progress) {if (progress < 0) {progress = 0;} else if (progress > 100) {progress = 100;}this.progress = progress;invalidate();}
}    

在布局文件中使用

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"android:gravity="center"><com.example.customview.CustomProgressBarandroid:id="@+id/customProgressBar"android:layout_width="200dp"android:layout_height="200dp" />
</LinearLayout>

在 Activity 中更新进度 

import android.os.Bundle;
import android.os.Handler;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;public class MainActivity extends AppCompatActivity {private CustomProgressBar customProgressBar;private int currentProgress = 0;private Handler handler = new Handler();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);customProgressBar = findViewById(R.id.customProgressBar);// 模拟进度更新new Thread(() -> {while (currentProgress < 100) {currentProgress++;handler.post(() -> customProgressBar.setProgress(currentProgress));try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}}handler.post(() -> Toast.makeText(MainActivity.this, "进度完成", Toast.LENGTH_SHORT).show());}).start();}
}

场景二：自定义星级评分控件

在电商、社交等应用里，星级评分控件是很常见的。下面来实现一个简单的星级评分控件。

实现思路

• 继承 View 类。
• 重写 onDraw 方法，绘制星星图标。
• 重写 onTouchEvent 方法，处理触摸事件，实现星级选择。

示例代码

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;import androidx.core.content.ContextCompat;public class CustomStarRating extends View {private Drawable starFilled;private Drawable starEmpty;private int starCount = 5;private int rating = 0;private int starSize = 50;private int starSpacing = 10;public CustomStarRating(Context context) {super(context);init();}public CustomStarRating(Context context, AttributeSet attrs) {super(context, attrs);init();}public CustomStarRating(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);init();}private void init() {starFilled = ContextCompat.getDrawable(getContext(), android.R.drawable.star_big_on);starEmpty = ContextCompat.getDrawable(getContext(), android.R.drawable.star_big_off);}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);for (int i = 0; i < starCount; i++) {int left = i * (starSize + starSpacing);int top = 0;int right = left + starSize;int bottom = top + starSize;Drawable drawable = (i < rating) ? starFilled : starEmpty;drawable.setBounds(left, top, right, bottom);drawable.draw(canvas);}}@Overridepublic boolean onTouchEvent(MotionEvent event) {if (event.getAction() == MotionEvent.ACTION_DOWN) {float x = event.getX();int newRating = (int) (x / (starSize + starSpacing)) + 1;if (newRating > starCount) {newRating = starCount;} else if (newRating < 0) {newRating = 0;}rating = newRating;invalidate();return true;}return super.onTouchEvent(event);}public int getRating() {return rating;}public void setRating(int rating) {if (rating < 0) {rating = 0;} else if (rating > starCount) {rating = starCount;}this.rating = rating;invalidate();}
}    

在布局文件中使用 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"android:gravity="center"><com.example.customview.CustomStarRatingandroid:id="@+id/customStarRating"android:layout_width="wrap_content"android:layout_height="wrap_content" />
</LinearLayout>

在 Activity 中获取评分 

import android.os.Bundle;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;public class MainActivity extends AppCompatActivity {private CustomStarRating customStarRating;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);customStarRating = findViewById(R.id.customStarRating);// 设置初始评分customStarRating.setRating(3);// 获取评分int rating = customStarRating.getRating();Toast.makeText(this, "当前评分：" + rating, Toast.LENGTH_SHORT).show();}
}

场景三：实现一个自定义的圆角ImageView

实现思路

1. 继承 ImageView：创建一个新的类，继承自 ImageView。
2. 重写 onDraw 方法：在 onDraw 方法里，运用 Canvas 和 Paint 来绘制圆角矩形，并且把图片绘制到这个圆角矩形内。
3. 处理图片缩放：要保证图片能够正确地缩放以适应圆角矩形。

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.RectF;
import android.util.AttributeSet;
import androidx.appcompat.widget.AppCompatImageView;public class RoundedImageView extends AppCompatImageView {private float cornerRadius = 20; // 默认圆角半径public RoundedImageView(Context context) {super(context);}public RoundedImageView(Context context, AttributeSet attrs) {super(context, attrs);init(context, attrs);}public RoundedImageView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);init(context, attrs);}private void init(Context context, AttributeSet attrs) {// 可以在这里从属性中获取圆角半径// TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.RoundedImageView);// cornerRadius = a.getDimension(R.styleable.RoundedImageView_cornerRadius, cornerRadius);// a.recycle();}@Overrideprotected void onDraw(Canvas canvas) {int width = getWidth();int height = getHeight();// 创建一个圆角矩形路径Path path = new Path();RectF rect = new RectF(0, 0, width, height);path.addRoundRect(rect, cornerRadius, cornerRadius, Path.Direction.CW);canvas.clipPath(path);super.onDraw(canvas);}public void setCornerRadius(float radius) {this.cornerRadius = radius;invalidate();}
}    

使用方法

在布局文件中使用自定义的 RoundedImageView：

<com.example.yourpackage.RoundedImageViewandroid:layout_width="200dp"android:layout_height="200dp"android:src="@drawable/your_image" />    

代码解释

1. RoundedImageView 类：继承自 AppCompatImageView，它是 ImageView 的兼容版本。
2. cornerRadius 变量：用来存储圆角的半径，默认值为 20。
3. init 方法：能够从属性中获取圆角半径，不过当前处于注释状态。
4. onDraw 方法：
   • 创建一个圆角矩形路径。
   • 运用 canvas.clipPath 方法把画布裁剪成圆角矩形。
   • 调用 super.onDraw(canvas) 来绘制图片。
5. setCornerRadius 方法：用于动态设置圆角半径，并且调用 invalidate 方法重新绘制视图。

之后还会有补充的，感谢观看！！！