public class AudioBar extends View{
private Paint mTextPaint;
public AudioBar(Context context) {
this(context,null);
}
public AudioBar(Context context, AttributeSet attrs) {
this(context, attrs,0);
}
public AudioBar(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
mTextPaint = new TextPaint();
mTextPaint.setColor(Color.RED);
}
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
width = getMeasuredWidth() ;
height = getMeasuredHeight();
int mRectCount = 0;
for(int count = 5 ; count < width ;count += mRectWidth){
mRectCount ++ ;
}
for(int i = 0 ; i < mRectCount ; i ++){
double mRandom = Math.random();
mRectHeight = (float) (height * mRandom);
canvas.drawRect(offset + mRectWidth * i,
mRectHeight,
mRectWidth * (i+1),
height,
mTextPaint);
}
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.sanhuimusic.mycustomview.MainActivity">
<com.sanhuimusic.mycustomview.view.AudioBar
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</LinearLayout>

public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int leftPadding = getPaddingLeft();
int topPadding = getPaddingTop();
int rightPadding = getPaddingRight();
int bottomPadding = getPaddingBottom();
width = getMeasuredWidth() - leftPadding - rightPadding;
height = getMeasuredHeight()- topPadding - bottomPadding;
int mRectCount = 0;
for(int count = 5 ; count < width ;count += mRectWidth){
mRectCount ++ ;
}
for(int i = 0 ; i < mRectCount ; i ++){
double mRandom = Math.random();
mRectHeight = (float) (height * mRandom);
canvas.drawRect(offset + mRectWidth * i,
mRectHeight,
mRectWidth * (i+1),
height,
mTextPaint);
}
postInvalidateDelayed(500);
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.sanhuimusic.mycustomview.MainActivity">
<com.sanhuimusic.mycustomview.view.AudioBar
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</LinearLayout>

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}

public static int getDefaultSize(int size, int measureSpec) {
int result = size;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
switch (specMode) {
case MeasureSpec.UNSPECIFIED:
result = size;
break;
case MeasureSpec.AT_MOST:
case MeasureSpec.EXACTLY:
result = specSize;
break;
}
return result;
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSpecSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSpecSize = MeasureSpec.getSize(heightMeasureSpec);
if(widthSpecMode == MeasureSpec.AT_MOST && heightSpecMode == MeasureSpec.AT_MOST){
setMeasuredDimension(getMeasuredWidth()/2 , getMeasuredHeight()/2);
} else if(widthSpecMode == MeasureSpec.AT_MOST){
setMeasuredDimension(getMeasuredWidth()/2 ,heightSpecSize);
} else if(heightSpecMode == MeasureSpec.AT_MOST){
setMeasuredDimension(widthSpecSize ,getMeasuredHeight()/2);
}
}